Circuit quantum electrodynamics is one of the most promising platforms for efficient quantum simulation and computation. In recent groundbreaking experiments, the immense flexibility of superconducting microwave resonators was utilized to realize hyperbolic lattices that emulate quantum physics in negatively curved space. Here we investigate experimentally feasible settings in which a few superconducting qubits are coupled to a bath of photons evolving on the hyperbolic lattice. We compare our numerical results for finite lattices with analytical results for continuous hyperbolic space on the Poincar{\'e} disk. We find good agreement between the two descriptions in the long-wavelength regime. We show that photon-qubit bound states have a curvature-limited size. We propose to use a qubit as a local probe of the hyperbolic bath, for example, by measuring the relaxation dynamics of the qubit. We find that, although the boundary effects strongly impact the photonic density of states, the spectral density is well described by the continuum theory. We show that interactions between qubits are mediated by photons propagating along geodesics. We demonstrate that the photonic bath can give rise to geometrically frustrated hyperbolic quantum spin models with finite-range or exponentially decaying interaction.

}, doi = {10.1103/PhysRevLett.128.013601}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.128.013601}, author = {Bienias, Przemyslaw and Boettcher, Igor and Belyansky, Ron and Kollar, Alicia J. and Gorshkov, Alexey V.} } @article { WOS:000739631400008, title = {Design of an Integrated Bell-State Analyzer on a Thin-Film Lithium Niobate Platform}, journal = {IEEE Photonics J.}, volume = {14}, number = {1}, year = {2022}, month = {FEB}, publisher = {IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC}, type = {Article}, abstract = {Trapped ions are excellent candidates for quantum computing and quantum networks because of their long coherence times, ability to generate entangled photons as well as high fidelity single- and two-qubit gates. To scale up trapped ion quantum computing, we need a Bell-state analyzer on a reconfigurable platform that can herald high fidelity entanglement between ions. In this work, we design a photonic Bell-state analyzer on a reconfigurable thin-film lithium niobate platform for polarization-encoded qubits. We optimize the device to achieve high fidelity entanglement between two trapped ions and find >99\% fidelity. Apart from that, the directional coupler used in our design can achieve any polarization-independent power splitting ratio which can have a rich variety of applications in the integrated photonic technology. The proposed device can scale up trapped ion quantum computing as well as other optically active spin qubits, such as color centers in diamond, quantum dots, and rare-earth ions.}, keywords = {Bell-state analyzer, Couplings, entanglement, ions, Lithium niobate, optical waveguides, Photonics, polarization qubits, polarization-independent directional coupler, Ports (computers), QUBIT, scalable quantum computing, thin-film lithium niobate, trapped ions}, issn = {1943-0655}, doi = {10.1109/JPHOT.2021.3136502}, author = {Saha, Uday and Waks, Edo} } @article { WOS:000727004500001, title = {Dynamical evolution and decay of multi-charged quantum vortex in a Bose-Einstein condensate}, journal = {Laser Phys. Lett.}, volume = {19}, number = {1}, year = {2022}, month = {JAN}, publisher = {IOP Publishing Ltd}, type = {Article}, abstract = {We report the observation of the twisted decay of quadruply charged vortices taking place in an atomic Bose-Einstein condensate. Supporting numerical simulations show that the singly-charged vortices, which result from the decay of a multi-charged vortex, twist around intertwined in the shape of helical Kelvin waves.}, keywords = {Bose-Einstein condensates, Kelvin waves, multiply charged vortices}, issn = {1612-2011}, doi = {10.1088/1612-202X/ac3d24}, author = {Telles, G. D. and Tavares, P. E. S. and Fritsch, A. R. and Cidrim, A. and Bagnato, V. S.} } @article { WOS:000742858100004, title = {Effective field theories of topological crystalline insulators and topological crystals}, journal = {Phys. Rev. B}, volume = {105}, number = {4}, year = {2022}, month = {JAN 7}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We present a general approach to obtain effective field theories for topological crystalline insulators whose low-energy theories are described by massive Dirac fermions. We show that these phases are characterized by the responses to spatially dependent mass parameters with interfaces. These mass interfaces implement the dimensional reduction procedure such that the state of interest is smoothly deformed into a topological crystal, which serves as a representative state of a phase in the general classification. Effective field theories are obtained by integrating out the massive Dirac fermions, and various quantized topological terms are uncovered. Our approach can be generalized to other crystalline symmetry-protected topological phases and provides a general strategy to derive effective field theories for such crystalline topological phases.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.105.045112}, author = {Huang, Sheng-Jie and Hsieh, Chang-Tse and Yu, Jiabin} } @article { WOS:000731820900002, title = {High-Q slow light and its localization in a photonic crystal microring}, journal = {Nat. Photonics}, volume = {16}, number = {1}, year = {2022}, month = {JAN}, pages = {66+}, publisher = {NATURE PORTFOLIO}, type = {Article}, abstract = {We introduce a photonic crystal ring cavity that resembles an internal gear and unites photonic crystal (PhC) and whispering gallery mode (WGM) concepts. This {\textquoteleft}microgear{\textquoteright} photonic crystal ring (MPhCR) is created by applying a periodic modulation to the inside boundary of a microring resonator to open a large bandgap, as in a PhC cavity, while maintaining the ring{\textquoteright}s circularly symmetric outside boundary and high optical quality factor (Q), as in a WGM cavity. The MPhCR targets a specific WGM to open a large PhC bandgap up to tens of free spectral ranges, compressing the mode spectrum while maintaining the high-Q, angular momenta and waveguide coupling properties of the WGM modes. In particular, near the dielectric band edge, we observe modes whose group velocity is slowed down by 10 times relative to conventional microring modes while supporting Q = (1.1 +/- 0.1) x 10(6). This Q is around 50 times that of the previous record in slow-light devices. Using the slow-light design as a starting point, we further demonstrate the ability to localize WGMs into photonic crystal defect modes, enabling a more than 10 times reduction of mode volume compared with conventional WGMs while maintaining a high Q value of up to (5.6 +/- 0.1) x 10(5). Importantly, this additional photonic crystal defect localization is achievable without requiring detailed electromagnetic design. Moreover, controlling their resonance frequencies and waveguide coupling is straightforward in the MPhCR, owing to its WGM heritage. In using a PhC to strongly modify the fundamental properties of WGMs, such as group velocity and localization, the MPhCR provides an exciting platform for a broad range of photonics applications, including sensing/metrology, nonlinear optics and cavity quantum electrodynamics.}, issn = {1749-4885}, doi = {10.1038/s41566-021-00912-w}, author = {Lu, Xiyuan and McClung, Andrew and Srinivasan, Kartik} } @article { WOS:000704382500004, title = {PyLCP: A Python package for computing laser cooling physics}, journal = {Comput. Phys. Commun.}, volume = {270}, year = {2022}, month = {JAN}, publisher = {ELSEVIER}, type = {Article}, abstract = {We present a Python object-oriented computer program for simulating various aspects of laser cooling physics. Our software is designed to be both easy to use and adaptable, allowing the user to specify the level structure, magnetic field profile, or the laser beams{\textquoteright} geometry, detuning, and intensity. The program contains three levels of approximation for the motion of the atom, applicable in different regimes offering cross checks for calculations and computational efficiency depending on the physical situation. We test the software by reproducing well-known phenomena, such as damped Rabi flopping, electromagnetically induced transparency, stimulated Raman adiabatic passage, and optical molasses. We also use our software package to quantitatively simulate recoil-limited magneto-optical traps, like those formed on the narrow S-1(0) -> P-3(1) transition in Sr-88 and Sr-87. (C) 2021 Published by Elsevier B.V.}, keywords = {atomic physics, laser cooling, python}, issn = {0010-4655}, doi = {10.1016/j.cpc.2021.108166}, author = {Eckel, Stephen and Barker, Daniel S. and Norrgard, Eric B. and Scherschligt, Julia} } @article {23676, title = {Strained bilayer graphene, emergent energy scales, and moir{\'e} gravity}, journal = {Phys. Rev. Research}, volume = {4}, year = {2022}, month = {May}, pages = {L022027}, abstract = {Twisted bilayer graphene is a rich condensed matter system, which allows one to tune energy scales and electronic correlations. The low-energy physics of the resulting moir{\'e} structure can be mathematically described in terms of a diffeomorphism in a continuum formulation. We stress that twisting is just one example of moir{\'e} diffeomorphisms. Another particularly simple and experimentally relevant transformation is a homogeneous isomorphic strain of one of the layers, which gives rise to a nearly identical moir{\'e} pattern (rotated by\ 90 degrees\ relative to the twisted structure) and potentially flat bands. We further observe that low-energy physics of the strained bilayer graphene takes the form of a theory of fermions tunneling between two curved space-times. Conformal transformation of the metrics results in emergent {\textquotedblleft}moir{\'e} energy scales,{\textquotedblright} which can be tuned to be much lower than those in the native theory. This observation generalizes to an arbitrary space-time dimension with or without an underlying lattice or periodicity and suggests a family of toy models of {\textquotedblleft}moir{\'e} gravity{\textquotedblright} with low emergent energy scales. Motivated by these analogies, we present an explicit toy construction of moir{\'e} gravity, where the effective cosmological constant can be made arbitrarily small. We speculate about possible relevance of this scenario to the fundamental vacuum catastrophe in cosmology.

}, doi = {10.1103/PhysRevResearch.4.L022027}, url = {https://link.aps.org/doi/10.1103/PhysRevResearch.4.L022027}, author = {Parhizkar, Alireza and Galitski, Victor} } @article {23481, title = {Unifying Quantum and Classical Speed Limits on Observables}, journal = {Phys. Rev. X}, volume = {12}, year = {2022}, month = {Feb}, pages = {011038}, abstract = {The presence of noise or the interaction with an environment can radically change the dynamics of observables of an otherwise isolated quantum system. We derive a bound on the speed with which observables of open quantum systems evolve. This speed limit is divided into Mandelstam and Tamm{\textquoteright}s original time-energy uncertainty relation and a time-information uncertainty relation recently derived for classical systems, and both are generalized to open quantum systems. By isolating the coherent and incoherent contributions to the system dynamics, we derive both lower and upper bounds on the speed of evolution. We prove that the latter provide tighter limits on the speed of observables than previously known quantum speed limits and that a preferred basis of speed operators serves to completely characterize the observables that saturate the speed limits. We use this construction to bound the effect of incoherent dynamics on the evolution of an observable and to find the Hamiltonian that gives the maximum coherent speedup to the evolution of an observable.

}, keywords = {limits, Observables}, doi = {10.1103/PhysRevX.12.011038}, url = {https://link.aps.org/doi/10.1103/PhysRevX.12.011038}, author = {Garcia-Pintos, Luis Pedro and Nicholson, Schuyler B. and Green, Jason R. and del Campo, Adolfo and Gorshkov, Alexey V.} } @article { WOS:000711685600005, title = {Acoustic-Phonon-Mediated Superconductivity in Rhombohedral Trilayer Graphene}, journal = {Phys. Rev. Lett.}, volume = {127}, number = {18}, year = {2021}, month = {OCT 29}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Motivated by the observation of two distinct superconducting phases in the moireless ABC-stacked rhombohedral trilayer graphene, we investigate the electron-acoustic-phonon coupling as a possible pairing mechanism. We predict the existence of superconductivity with the highest T-c similar to 3 K near the Van Hove singularity. Away from the Van Hove singularity, T-c remains finite in a wide range of doping. In our model, the s-wave spin-singlet and f-wave spin-triplet pairings yield the same T-c, while other pairing states have negligible T-c. Our theory provides a simple explanation for the two distinct superconducting phases in the experiment and suggests that superconductivity and other interaction-driven phases (e.g., ferromagnetism) can have different origins.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.127.187001}, author = {Chou, Yang-Zhi and Wu, Fengcheng and Sau, Jay D. and Das Sarma, Sankar} } @article {ahn_anisotropic_2021, title = {Anisotropic fermionic quasiparticles}, journal = {Phys. Rev. B}, volume = {103}, number = {4}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {jan}, abstract = {We have carried out a comprehensive investigation of the quasiparticle properties of a two-dimensional electron gas, interacting via the long-range Coulomb interaction in the presence of bare mass anisotropy (i.e., with an elliptic noninteracting Fermi surface) by calculating the self-energy, the spectral function, the scattering rate, and the effective mass within the leading-order dynamical self-energy approximation. Our theory is exact in the high-density limit. We find anisotropic features of quasiparticle properties that are not captured by the commonly used isotropic approximation where the anisotropic effective mass is replaced by the isotropic averaged density-of-states mass. Some of these interesting results are as follows: (1) The many-body renormalization of the quasiparticle spectrum becomes highly anisotropic as the quasiparticle energy increases away from the Fermi energy; (2) the interaction-induced inelastic-scattering rate features a strong anisotropy, exhibiting an abrupt jump at different injected energies depending on the momentum direction of the injected electron; (3) the effective-mass enhancement is larger (smaller) for the light (heavy) mass, showing that the anisotropy is reduced by interactions. Our results and analysis show that the unjustified neglect of the mass anisotropy can lead to an incorrect description of quasiparticle properties of the anisotropic system and inaccurate estimates of physical quantities of interest although the use of an equivalent isotropic approximation using the density-of-states effective mass as is commonly and uncritically performed in the literature, works as a reasonable approximation in many situations. In addition to the complete random phase approximation theory for the anisotropic quasiparticles, we also provide a theory using the simpler plasmon-pole approximation, commenting on its validity for anisotropic self-energy calculations. We comment also on the interaction effect on the Fermi-surface topology, finding that the elliptic shape of the bare Fermi surface is preserved with suppressed ellipticity in the interacting system to a high degree of accuracy except in the very strongly interacting limit (and for very high bare mass anisotropy). Our theory provides a complete generalization of the existing isotropic many-body theory of interacting electrons to the corresponding anisotropic systems.

}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.045303}, author = {Ahn, Seongjin and Sankar Das Sarma} } @article { WOS:000680428500001, title = {Anomalies and unusual stability of multicomponent Luttinger liquids in Z(n) x Z(n) spin chains}, journal = {Phys. Rev. B}, volume = {104}, number = {4}, year = {2021}, month = {JUL 30}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study translationally invariant spin chains where each unit cell contains an n-state projective representation of a Z(n) x Z(n) internal symmetry, generalizing the spin-1/2 XYZ chain. Such spin chains possess a generalized Lieb-Schultz-Mattis (LSM) constraint, and we demonstrate that certain (n - 1)-component Luttinger liquids possess the correct anomalies to satisfy these LSM constraints. For n = 3, using both numerical and analytical approaches, we find that such spin chains with nearest-neighbor interactions appear to be gapless for a wide range of microscopic parameters and described by a two-component conformally invariant Luttinger liquid. This implies the emergence of n - 1 conserved U(1) charges from only discrete microscopic symmetries. Remarkably, the system remains gapless for an unusually large parameter regime despite the apparent existence of symmetryallowed relevant operators in the field theory. This suggests that either these spin chains have hidden conserved quantities not previously identified, or the parameters of the field theory are simply unusual due to frustration effects of the lattice Hamiltonian. We argue that similar features are expected to occur in (1) Z(n) x Z(n) symmetric chains for n odd and (2) S-n x Z(n) symmetric chains for all n > 2. Finally, we suggest the possibility of a lower bound growing with n on the minimum central charge of field theories that possess such LSM anomalies.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.104.045151}, author = {Alavirad, Yahya and Barkeshli, Maissam} } @article { WOS:000681427700009, title = {Anomalous Floquet Chiral Topological Superconductivity in a Topological Insulator Sandwich Structure}, journal = {Phys. Rev. Lett.}, volume = {127}, number = {6}, year = {2021}, month = {AUG 5}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We show that Floquet chiral topological superconductivity arises naturally in Josephson junctions made of magnetic topological insulator-superconductor sandwich structures. The Josephson phase modulation associated with an applied bias voltage across the junction drives the system into the anomalous Floquet chiral topological superconductor hosting chiral Majorana edge modes in the quasienergy spectrum, with the bulk Floquet bands carrying zero Chern numbers. The bias voltage acts as a tuning parameter enabling novel Floquet topological quantum phase transitions driving the system into a myriad of exotic Majorana-carrying Floquet topological superconducting phases. Our theory establishes a new paradigm for realizing Floquet chiral topological superconductivity in solid-state systems, which should be experimentally directly accessible.

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.127.067001}, author = {Zhang, Rui-Xing and Sankar Das Sarma} } @article { WOS:000704665100001, title = {Asymmetric Blockade and Multiqubit Gates via Dipole-Dipole Interactions}, journal = {Phys. Rev. Lett.}, volume = {127}, number = {12}, year = {2021}, month = {SEP 17}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Because of their strong and tunable interactions, Rydberg atoms can be used to realize fast two-qubit entangling gates. We propose a generalization of a generic two-qubit Rydberg-blockade gate to multiqubit Rydberg-blockade gates that involve both many control qubits and many target qubits simultaneously. This is achieved by using strong microwave fields to dress nearby Rydberg states, leading to asymmetric blockade in which control-target interactions are much stronger than control-control and target-target interactions. The implementation of these multiqubit gates can drastically simplify both quantum algorithms and state preparation. To illustrate this, we show that a 25-atom Greenberger-Horne-Zeilinger state can be created using only three gates with an error of 5.8\%.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.127.120501}, author = {Young, Jeremy T. and Bienias, Przemyslaw and Belyansky, Ron and Kaufman, Adam M. and Gorshkov, V, Alexey} } @article { WOS:000722573400002, title = {Band manipulation and spin texture in interacting moire helical edges}, journal = {Phys. Rev. B}, volume = {104}, number = {20}, year = {2021}, month = {NOV 23}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We develop a theory for manipulating the effective band structure of interacting helical edge states realized on the boundary of two-dimensional time-reversal symmetric topological insulators. For a sufficiently strong interaction, an interacting edge band gap develops, spontaneously breaking time-reversal symmetry on the edge. The resulting spin texture, as well as the energy of the time-reversal breaking gaps, can be tuned by an external moire potential (i.e., a superlattice potential). Remarkably, we establish that by tuning the strength and period of the potential, the interacting gaps can be fully suppressed and interacting Dirac points reemerge. In addition, nearly flat bands can be created by the moire potential with a sufficiently long period. Our theory provides an unprecedented way to enhance the coherence length of interacting helical edges by suppressing the interacting gap. The implications of this finding for ongoing experiments on helical edge states is discussed.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.104.L201113}, author = {Chou, Yang-Zhi and Cano, Jennifer and Pixley, J. H.} } @article {lee_bright_2021, title = {Bright {Telecom}-{Wavelength} {Single} {Photons} {Based} on a {Tapered} {Nanobeam}}, journal = {Nano Lett.}, volume = {21}, number = {1}, year = {2021}, note = {Place: 1155 16TH ST, NW, WASHINGTON, DC 20036 USA Publisher: AMER CHEMICAL SOC Type: Article}, month = {jan}, pages = {323{\textendash}329}, abstract = {Telecom-wavelength single photons are essential components for long-distance quantum networks. However, bright and pure single photon sources at telecom wavelengths remain challenging to achieve. Here, we demonstrate a bright telecom-wavelength single photon source based on a tapered nanobeam containing InAs/InP quantum dots. The tapered nanobeam enables directional and Gaussian-like far-field emission of the quantum dots. As a result, using above-band excitation we obtain an end-to-end brightness of 4.1 +/- 0.1\% and first-lens brightness of 27.0 +/- 0.1\% at the -1300 nm wavelength. Furthermore, we adopt quasi-resonant excitation to reduce both multiphoton emission and decoherence from unwanted charge carriers. As a result, we achieve a coherence time of 523 +/- 16 ps and postselected Hong-Ou-Mandel visibility of 0 .91 +/- 0.09 along with a comparable first-lens brightness of 21.0 +/- 0.1\%. These results represent a major step toward a practical fiber-based single photon source at telecom wavelengths for long-distance quantum networks.

}, keywords = {Quantum Dots, single photon sources, telecom wavelength, two-photon interference}, issn = {1530-6984}, doi = {10.1021/acs.nanolett.0c03680}, author = {Lee, Chang-Min and Buyukkaya, Mustafa Atabey and Harper, Samuel and Aghaeimeibodi, Shahriar and Richardson, Christopher J. K. and Waks, Edo} } @article {sosnova_character_2021, title = {Character of motional modes for entanglement and sympathetic cooling of mixed-species trapped-ion chains}, journal = {Phys. Rev. A}, volume = {103}, number = {1}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, abstract = {Modular mixed-species ion-trap networks are a promising framework for scalable quantum information processing, where one species acts as a memory qubit and another as a communication qubit. This architecture requires high-fidelity mixed-species entangling gates to transfer information from communication to memory qubits through their collective motion. We investigate the character of the motional modes of mixed-species ion chains of various lengths and in various trap potentials for entangling operations and sympathetic cooling. We find that the laser power required for high-fidelity entangling gates based on transverse modes is at least an order of magnitude higher than that for gates based on axial modes for ion species with a large mass ratio. We also find that for even moderate mass differences, the transverse modes are much harder to cool than the axial modes regardless of the ion chain configuration. Therefore, transverse modes conventionally used for operations in single-species ion chains may not be well suited for mixed-species chains with widely different masses.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.103.012610}, author = {Sosnova, K. and Carter, A. and Monroe, C.} } @article { WOS:000678812000001, title = {Charge density wave and finite-temperature transport in minimally twisted bilayer graphene}, journal = {Phys. Rev. B}, volume = {104}, number = {4}, year = {2021}, month = {JUL 28}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study phenomena driven by electron-electron interactions in the minimally twisted bilayer graphene (mTBLG) with a perpendicular electric field. The low-energy degrees of freedom in mTBLG are governed by a network of one-dimensional domain-wall states, described by two channels of one-dimensional linearly dispersing spin-1/2 fermions. We show that the interaction can realize a spin-gapped interchannel charge density wave (CDW) state at low temperatures, forming a {\textquoteleft}{\textquoteleft}Coulomb drag{{\textquoteright}{\textquoteright}} between the channels and leaving only one charge conducting mode. For sufficiently high temperatures, power-law-in-temperature resistivity emerges from the charge Umklapp scatterings within a domain wall. Remarkably, the presence of the CDW states can strengthen the charge Umklapp scattering and induce a resistivity minimum at an intermediate temperature corresponding to the CDW correlation energy. We further discuss the conditions that resistivity of the network is dominated by the domain walls. In particular, the power-law-in-temperature resistivity results can apply to other systems that manifest topological domain-wall structures.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.104.045146}, author = {Chou, Yang-Zhi and Wu, Fengcheng and Sau, Jay D.} } @article { WOS:000725520100002, title = {Charge-Impurity Effects in Hybrid Majorana Nanowires}, journal = {Phys. Rev. Appl.}, volume = {16}, number = {5}, year = {2021}, month = {NOV 30}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We address an outstanding problem that represents a critical roadblock in the development of the Majorana-based topological qubit using semiconductor-superconductor hybrid structures: the quantitative characterization of disorder effects generated by the unintentional presence of charge impurities within the hybrid device. Given that disorder can have far-reaching consequences for the Majorana physics but is intrinsically difficult to probe experimentally in a hybrid structure, providing a quantitative theoretical description of disorder effects becomes essential. To accomplish this task, we develop a microscopic theory that (i) provides a quantitative characterization of the effective potential generated by a charge impurity embedded inside a semiconductor wire proximity coupled to a superconductor layer by solving selfconsistently the associated three-dimensional Schrodinger-Poisson problem, (ii) describes the low-energy physics of the hybrid structure in the presence of s-wave superconductivity, spin-orbit coupling, Zeeman splitting, and disorder arising from multiple charge impurities by using the results of (i) within a standard free-fermion approach, and (iii) links the microscopic results to experimentally observable features by generating tunneling differential-conductance maps as a function of the control parameters (e.g., Zeeman field and chemical potential). We find that charge impurities lead to serious complications regarding the realization and observation of Majorana zero modes, which have direct implications for the development of Majorana-based qubits. More importantly, our work provides a clear direction regarding what needs to be done for progress in the field, including specific materials-quality and semiconductor-purity targets that must be achieved to create a topological qubit.}, issn = {2331-7019}, doi = {10.1103/PhysRevApplied.16.054053}, author = {Woods, Benjamin D. and Das Sarma, Sankar and Stanescu, Tudor D.} } @article { WOS:000652838200010, title = {Chiral Anomaly in Interacting Condensed Matter Systems}, journal = {Phys. Rev. Lett.}, volume = {126}, number = {18}, year = {2021}, month = {MAY 7}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The chiral anomaly is a fundamental quantum mechanical phenomenon which is of great importance to both particle physics and condensed matter physics alike. In the context of QED, it manifests as the breaking of chiral symmetry in the presence of electromagnetic fields. It is also known that anomalous chiral symmetry breaking can occur through interactions alone, as is the case for interacting one-dimensional systems. In this Letter, we investigate the interplay between these two modes of anomalous chiral symmetry breaking in the context of interacting Weyl semimetals. Using Fujikawa{\textquoteright}s path integral method, we show that the chiral charge continuity equation is modified by the presence of interactions which can be viewed as including the effect of the electric and magnetic fields generated by the interacting quantum matter. This can be understood further using dimensional reduction and a Luttinger liquid description of the lowest Landau level. These effects manifest themselves in the nonlinear response of the system. In particular, we find an interaction-dependent density response due to a change in the magnetic field as well as a contribution to the nonequilibrium and inhomogeneous anomalous Hall response while preserving its equilibrium value.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.126.185303}, author = {Rylands, Colin and Parhizkar, Alireza and Burkov, Anton A. and Galitski, Victor} } @article { WOS:000674773400001, title = {Circulation by Microwave-Induced Vortex Transport for Signal Isolation}, journal = {PRX Quantum}, volume = {2}, number = {3}, year = {2021}, month = {JUL 15}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Magnetic fields break time-reversal symmetry, which is leveraged in many settings to enable the nonreciprocal behavior of light. This is the core physics of circulators and other elements used in a variety of microwave and optical settings. Commercial circulators in the microwave domain typically use ferromagnetic materials and wave interference, requiring large devices and large fields. However, quantum information devices for sensing and computation require small sizes, lower fields, and better on-chip integration. Equivalences to ferromagnetic order-such as the XY model-can be realized at much lower magnetic fields by use of arrays of superconducting islands connected by Josephson junctions. Here we show that the quantum-coherent motion of a single vortex in such an array suffices to induce nonreciprocal behavior, enabling a small-scale, moderate-bandwidth, and low insertion loss circulator at very low magnetic fields and at microwave frequencies relevant for experiments with qubits.}, doi = {10.1103/PRXQuanttun.2.030309}, author = {Richman, Brittany and Taylor, Jacob M.} } @article { WOS:000655871200003, title = {Classical model for sub-Planckian thermal diffusivity in complex crystals}, journal = {Phys. Rev. B}, volume = {103}, number = {18}, year = {2021}, month = {MAY 10}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Measurements of thermal diffusivity in several insulators have been shown to reach a Planckian bound on thermal transport that can be thought of as the limit of validity of semiclassical phonon scattering. Beyond this regime, the heat transport must be understood in terms of incoherent motion of the atoms under strongly anharmonic interactions. In this work, we propose a model for heat transport in a strongly anharmonic system where the thermal diffusivity can be lower than the Planckian thermal diffusivity bound. Similar to the materials that exhibit thermal diffusivity close to this bound, our scenario involves complex unit cells with incoherent intra-cell dynamics. We derive a general formalism to compute thermal conductivity in such cases with anharmonic intra-cell dynamics coupled to nearly harmonic inter-cell coupling. Through direct numerical simulation of the nonlinear unit-cell motion, we explicitly show that our model allows sub-Planckian thermal diffusivity. We find that the propagator of the acoustic phonons becomes incoherent throughout most of the Brillouin zone in this limit. We expect these features to apply to more realistic models of complex insulators showing sub-Planckian thermal diffusivity, suggesting a multispecies generalization of the thermal diffusivity bound that is similar to the viscosity bound in fluids.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.184305}, author = {Wu, Huan-Kuang and Sau, Jay D.} } @article { WOS:000698806700001, title = {CODATA Recommended Values of the Fundamental Physical Constants: 2018}, journal = {J. Phys. Chem. Ref. Data}, volume = {50}, number = {3}, year = {2021}, month = {SEP 1}, publisher = {AIP Publishing}, type = {Article}, abstract = {We report the 2018 self-consistent values of constants and conversion factors of physics and chemistry recommended by the Committee on Data of the International Science Council. The recommended values can also be found at physics.nist.gov/constants. The values are based on a least-squares adjustment that takes into account all theoretical and experimental data available through 31 December 2018. A discussion of the major improvements as well as inconsistencies within the data is given. The former include a decrease in the uncertainty of the dimensionless fine-structure constant and a nearly two orders of magnitude improvement of particle masses expressed in units of kg due to the transition to the revised International System of Units (SI) with an exact value for the Planck constant. Further, because the elementary charge, Boltzmann constant, and Avogadro constant also have exact values in the revised SI, many other constants are either exact or have significantly reduced uncertainties. Inconsistencies remain for the gravitational constant and the muon magnetic-moment anomaly. The proton charge radius puzzle has been partially resolved by improved measurements of hydrogen energy levels. (c) 2021 by the U.S. Secretary of Commerce on behalf of the United States. All rights reserved.}, keywords = {conventional and SI electrical units, electron and muon g-factors, fine-structure constant, fundamental constants, precision measurements, proton radius, QED, revised SI, Rydberg constant}, issn = {0047-2689}, doi = {10.1063/5.0064853}, author = {Tiesinga, Eite and Mohr, Peter J. and Newell, David B. and Taylor, Barry N.} } @article { WOS:000669060200001, title = {CODATA recommended values of the fundamental physical constants: 2018}, journal = {Rev. Mod. Phys.}, volume = {93}, number = {2}, year = {2021}, month = {JUN 30}, publisher = {AMER PHYSICAL SOC}, type = {Review}, abstract = {We report the 2018 self-consistent values of constants and conversion factors of physics and chemistry recommended by the Committee on Data of the International Science Council (CODATA). The recommended values can also be found at physics.nist.gov/constants. The values are based on a least-squares adjustment that takes into account all theoretical and experimental data available through 31 December 2018. A discussion of the major improvements as well as inconsistencies within the data is given. The former include a decrease in the uncertainty of the dimensionless fine-structure constant and a nearly two orders of magnitude improvement of particle masses expressed in units of kg due to the transition to the revised International System of Units (SI) with an exact value for the Planck constant. Further, because the elementary charge, Boltzmann constant, and Avogadro constant also have exact values in the revised SI, many other constants are either exact or have significantly reduced uncertainties. Inconsistencies remain for the gravitational constant and the muon magnetic-moment anomaly. The proton charge radius puzzle has been partially resolved by improved measurements of hydrogen energy levels.}, issn = {0034-6861}, doi = {10.1103/RevModPhys.93.025010}, author = {Tiesinga, Eite and Mohr, Peter J. and Newell, David B. and Taylor, Barry N.} } @article {liang_coherence_2021, title = {Coherence and decoherence in the {Harper}-{Hofstadter} model}, journal = {Phys. Rev. Res.}, volume = {3}, number = {2}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {apr}, abstract = {We quantum simulated the 2D Harper-Hofstadter (HH) lattice model in a highly elongated tube geometry-three sites in circumference-using an atomic Bose-Einstein condensate. In addition to the usual transverse (out-of-plane) magnetic flux, piercing the surface of the tube, we threaded a longitudinal flux Phi(L) down the axis of the tube. This geometry evokes an Aharonov-Bohm interferometer, where noise in Phi(L) would readily decohere the interference present in trajectories encircling the tube. We observe this behavior only when transverse flux is a rational fraction of the flux quantum and remarkably find that for irrational fractions the decoherence is absent. Furthermore, at rational values of transverse flux, we show that the time evolution averaged over the noisy longitudinal flux matches the time evolution at nearby irrational fluxes. Thus, the appealing intuitive picture of an Aharonov-Bohm interferometer is insufficient. Instead, we quantitatively explain our observations by transforming the HH model into a collection of momentum-space Aubry-Andre models.}, doi = {10.1103/PhysRevResearch.3.023058}, author = {Liang, Q-Y and Trypogeorgos, D. and Valdes-Curiel, A. and Tao, J. and Zhao, M. and Spielman, I. B.} } @article {burenkov_coherent_2021, title = {Coherent optical processes with an all-optical atomic simulator}, journal = {Opt. Express}, volume = {29}, number = {1}, year = {2021}, note = {Place: 2010 MASSACHUSETTS AVE NW, WASHINGTON, DC 20036 USA Publisher: OPTICAL SOC AMER Type: Article}, month = {jan}, pages = {330{\textendash}341}, abstract = {We show how novel photonic devices such as broadband quantum memory and efficient quantum frequency transduction can be implemented using three-wave mixing processes in a 1D array of nonlinear waveguides evanescently coupled to nearest neighbors. We do this using an analogy of an atom interacting with an external optical field using both classical and quantum models of the optical fields and adapting well-known coherent processes from atomic optics, such as electromagnetically induced transparency and stimulated Raman adiabatic passage to design. This approach allows the implementation of devices that are very difficult or impossible to implement by conventional techniques.

}, issn = {1094-4087}, doi = {10.1364/OE.415480}, author = {Burenkov, Ivan A. and Novikova, Irina and Tikhonova, Olga V and Polyakov, Sergey V} } @article { WOS:000662095800008, title = {Collisional excitation of C+(P-2) spin-orbit levels by molecular hydrogen revisited}, journal = {Mon. Not. Roy. Astron. Soc.}, volume = {501}, number = {1}, year = {2021}, month = {FEB}, pages = {L38-L42}, publisher = {OXFORD UNIV PRESS}, type = {Article}, abstract = {Relaxation of the spin-orbit excited C+(P-2(3/2)) ion by collisions with H-2 is an important process in the interstellar medium. Previous calculations of rate coefficients for this process employed potential energies computed for only collinear and perpendicular approach of H-2 to the ion. To capture the full angular dependence of the C+-H-2 interaction, the angular variation of the potential has been obtained by quantum chemical calculations in this work. These data were used to compute rate coefficients for the de-excitation of the C+(P-2(3/2)) level in collisions with H-2 in its j = 0, 1, and 2 rotational levels. With the assumption that the para-H-2 rotational levels are in Local Thermodynamic Equilibrium (LTE), rate coefficients were then calculated for de-excitation by para- and ortho-H-2 for temperature ranging from 5 to 500 K. The rate coefficient for de-excitation by para-H-2 is ca. 10 per cent higher at temperatures near 100 K but 10 per cent lower at temperatures greater than 300 K than the previous best calculation. By contrast, the de-excitation rate coefficient for ortho-H-2 is 15 per cent higher at low temperatures but approximately equal as compared with the previous best calculation. The impact of these new rate coefficients is briefly tested in radiative transfer calculations.}, keywords = {ISM: abundances, molecular data, molecular processes}, issn = {0035-8711}, doi = {10.1093/mnrasl/slaa192}, author = {Klos, Jacek and Dagdigian, Paul J. and Lique, Francois} } @article { WOS:000671590700016, title = {Comment on {\textquoteleft}{\textquoteleft}Fluctuations in Extractable Work Bound the Charging Power of Quantum Batteries{{\textquoteright}{\textquoteright}} Reply}, journal = {Phys. Rev. Lett.}, volume = {127}, number = {2}, year = {2021}, month = {JUL 9}, publisher = {AMER PHYSICAL SOC}, type = {Editorial Material}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.127.028902}, author = {Garcia-Pintos, Luis Pedro and Hamma, Alioscia and del Campo, Adolfo} } @article { WOS:000704077500001, title = {Complexity of Fermionic Dissipative Interactions and Applications to Quantum Computing}, journal = {PRX Quantum}, volume = {2}, number = {3}, year = {2021}, month = {SEP 24}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Interactions between particles are usually a resource for quantum computing, making quantum many-body systems intractable by any known classical algorithm. In contrast, noise is typically considered as being inimical to quantum many-body correlations, ultimately leading the system to a classically tractable state. This work shows that noise represented by two-body processes, such as pair loss, plays the same role as many-body interactions and makes otherwise classically simulable systems universal for quantum computing. We analyze such processes in detail and establish a complexity transition between simulable and nonsimulable systems as a function of a tuning parameter. We determine important classes of simulable and nonsimulable two-body dissipation. Finally, we show how using resonant dissipation in cold atoms can enhance the performance of two-qubit gates.}, doi = {10.1103/PRXQuantum.2.030350}, author = {Shtanko, Oles and Deshpande, Abhinav and Julienne, Paul S. and Gorshkov, V, Alexey} } @article { WOS:000674582200004, title = {Considering Photoinduced Second-Harmonic Generation as a dc Kerr Optical Parametric Oscillation or Amplification Process}, journal = {Phys. Rev. Appl.}, volume = {16}, number = {1}, year = {2021}, month = {JUL 12}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Photoinduced second-harmonic generation (SHG) in centrosymmetric materials like silica and silicon nitride has been commonly explained as an effective second-order (chi (2)) process mediated by a dc electric field and the medium{\textquoteright}s third-order (chi (3)) nonlinearity. In this explanation, the coherent photogalvanic effect is the source of a dc electric field whose spatial periodicity naturally enables quasi-phase-matching. While successful in explaining many observations from experiment, the behavior at low input powers, and in particular, the apparent existence of a threshold for efficient photoinduced SHG observed in some experiments has largely been overlooked theoretically. In this Paper, we reconsider photoinduced SHG within the framework of four-wave mixing (FWM), involving degenerate pump, second-harmonic signal, and dc electric field. We propose a hypothesis that photoinduced SHG is a FWM-mediated dc Kerr optical parametric oscillation or amplification process. This hypothesis can explain the threshold behavior, and moreover, predicts unconventional light amplification, both of which we verify by experiments in siliconnitride microresonators. Finally, we discuss the physical implications of our work in various platforms and future directions.}, issn = {2331-7019}, doi = {10.1103/PhysRevApplied.16.014027}, author = {Lu, Xiyuan and Srinivasan, Kartik} } @article { WOS:000720123400004, title = {Correlation-Induced Triplet Pairing Superconductivity in Graphene-Based Moire {\textquoteleft} Systems}, journal = {Phys. Rev. Lett.}, volume = {127}, number = {21}, year = {2021}, month = {NOV 15}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Motivated by the possible non-spin-singlet superconductivity in the magic-angle twisted trilayer graphene experiment, we investigate the triplet-pairing superconductivity arising from a correlationinduced spin-fermion model of Dirac fermions with spin, valley, and sublattice degrees of freedom. We find that the f-wave pairing is favored due to the valley-sublattice structure, and the superconducting state is time-reversal symmetric, fully gapped, and nontopological. With a small in-plane magnetic field, the superconducting state becomes partially polarized, and the transition temperature can be slightly enhanced. Our results apply qualitatively to Dirac fermions for the triplet-pairing superconductivity in graphene-based moire systems, which is fundamentally distinct from triplet superconductivity in 3He and ferromagnetic superconductors.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.127.217001}, author = {Chou, Yang-Zhi and Wu, Fengcheng and Sau, Jay D. and Das Sarma, Sankar} } @article { WOS:000664572100002, title = {Coulomb drag in topological wires separated by an air gap}, journal = {Nat. Electron.}, volume = {4}, number = {8}, year = {2021}, month = {AUG}, pages = {573-578}, publisher = {NATURE PORTFOLIO}, type = {Article}, abstract = {Measurements of one-dimensional Coulomb drag between adjacent edge states of quantum spin Hall insulators that are separated by an air gap suggest that quantum spin Hall effects could be used to suppress the impact of Coulomb interactions on the performance of future nanocircuits. Strong electron-electron interactions between adjacent nanoscale wires can lead to one-dimensional Coulomb drag, where current in one wire induces a voltage in the second wire via Coulomb interactions. This effect creates challenges for the development of nanoelectronic devices. Quantum spin Hall (QSH) insulators are a promising platform for the development of low-power electronic devices due to their topological protection of edge states from non-magnetic disorder. However, although Coulomb drag in QSH edges has been considered theoretically, experimental explorations of the effect remain limited. Here, we show that one-dimensional Coulomb drag can be observed between adjacent QSH edges that are separated by an air gap. The pair of one-dimensional helical edge states is created in split H-bar devices in inverted InAs/GaSb quantum wells. Near the Dirac point, negative drag signals dominate at low temperatures and exhibit a non-monotonic temperature dependence, suggesting that distinct drag mechanisms compete and cancel out at higher temperatures. The results suggest that QSH effects could be used to suppress the impact of Coulomb interactions on the performance of future nanocircuits.}, issn = {2520-1131}, doi = {10.1038/s41928-021-00603-y}, author = {Du, Lingjie and Zheng, Jianmin and Chou, Yang-Zhi and Zhang, Jie and Wu, Xingjun and Sullivan, Gerard and Ikhlassi, Amal and Du, Rui-Rui} } @article { WOS:000734372000007, title = {Counterexample to the conjectured Planckian bound on transport}, journal = {Phys. Rev. B}, volume = {104}, number = {23}, year = {2021}, month = {DEC 20}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {It has recently been conjectured that the transport relaxation rate in metals is bounded above by the temperature of the system. In this paper, we discuss the transport phenomenology of overdoped electron-doped cuprates, which we show constitute an unambiguous counterexample to this putative {\textquoteleft}{\textquoteleft}Planckian{{\textquoteright}{\textquoteright}} bound, raising serious questions about the efficacy of the bound.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.104.235138}, author = {Poniatowski, Nicholas R. and Sarkar, Tarapada and Lobo, Ricardo P. S. M. and Das Sarma, Sankar and Greene, Richard L.} } @article {curtis_critical_2021, title = {Critical theory for the breakdown of photon blockade}, journal = {Phys. Rev. Res.}, volume = {3}, number = {2}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, abstract = {Photon blockade is the result of the interplay between the quantized nature of light and strong optical nonlinearities, whereby strong photon-photon repulsion prevents a quantum optical system from absorbing multiple photons. We theoretically study a single atom coupled to the light field, described by the resonantly driven Jaynes-Cummings model, in which case the photon blockade breaks down in a second-order phase transition at a critical drive strength. We show that this transition is associated to the spontaneous breaking of an antiunitary PT symmetry. Within a semiclassical approximation, we calculate the expectation values of observables in the steady state. We then move beyond the semiclassical approximation and approach the critical point from the disordered (blockaded) phase by reducing the Lindblad quantum master equation to a classical rate equation that we solve. The width of the steady-state distribution in Fock space is found to diverge as we approach the critical point with a simple power law, allowing us to calculate the critical scaling of steady-state observables without invoking mean-field theory. We propose a simple physical toy model for biased diffusion in the space of occupation numbers, which captures the universal properties of the steady state. We list several experimental platforms where this phenomenon may be observed.}, doi = {10.1103/PhysRevResearch.3.023062}, author = {Curtis, Jonathan B. and Boettcher, Igor and Young, Jeremy T. and Maghrebi, Mohammad F. and Carmichael, Howard and Gorshkov, V, Alexey and Foss-Feig, Michael} } @article { WOS:000685104900003, title = {Crossover between trivial zero modes in Majorana nanowires}, journal = {Phys. Rev. B}, volume = {104}, number = {5}, year = {2021}, month = {AUG 12}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We consider the superconductor-semiconductor nanowire hybrid Majorana platform ({{\textquoteright}{\textquoteright}}Majorana nanowire{{\textquoteright}{\textquoteright}}) in the presence of a deterministic spatially slowly varying inhomogeneous chemical potential and a random spatial quenched potential disorder, both of which are known to produce nontopological almost-zero-energy modes mimicking the theoretically predicted topological Majorana zero modes. We study the crossover among these mechanisms by calculating the tunnel conductance while varying the relative strength between inhomogeneous potential and random disorder in a controlled manner. We find that the entire crossover region manifests abundant trivial zero modes, many of which showing the apparent {\textquoteleft}{\textquoteleft}quantization{{\textquoteright}{\textquoteright}} of the zero-bias conductance peak at 2e(2)/h, with occasional disorder-dominated peaks exceeding 2e(2)/h. We present animations of the simulated crossover behavior and discuss experimental implications. Additionally, in order to simulate the realistic disorder in experimental nanowires, we also study in depth the case of disorder arising from random individual static impurities along the wire, and consider crossover associated with such impurity effects. Our results, when compared qualitatively with existing Majorana nanowire experimental results, indicate the dominant role of random disorder in the experiments. It turns out that all three mechanisms may produce trivial zero-bias peaks in the tunnel conductance, and the crossover among these physical mechanisms (i.e., when more than one mechanism is present in the system) is smooth and continuous, making it difficult a priori to conclude which mechanism is dominant in a particular sample just by a casual inspection of the zero-bias conductance peaks.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.104.054510}, author = {Pan, Haining and Das Sarma, Sankar} } @article {manjunath_crystalline_2021, title = {Crystalline gauge fields and quantized discrete geometric response for {Abelian} topological phases with lattice symmetry}, journal = {Phys. Rev. Res.}, volume = {3}, number = {1}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {jan}, abstract = {Clean isotropic quantum Hall fluids in the continuum possess a host of symmetry-protected quantized invariants, such as the Hall conductivity, shift, and Hall viscosity. Here we develop a theory of symmetry-protected quantized invariants for topological phases defined on a lattice, where quantized invariants with no continuum analog can arise. We develop topological field theories using discrete crystalline gauge fields to fully characterize quantized invariants of (2 + 1)D Abelian topological orders with symmetry group G = U(1) x G(space), where G(space) consists of orientation-preserving space group symmetries on the lattice. We show how discrete rotational and translational symmetry fractionalization can be characterized by a discrete spin vector, a discrete torsion vector which has no analog in the continuum or in the absence of lattice rotation symmetry, and an area vector, which also has no analog in the continuum. The discrete torsion vector implies a type of crystal momentum fractionalization that is only nontrivial for two, three, and fourfold rotation symmetry. The quantized topological response theory includes a discrete version of the shift, which binds fractional charge to disclinations and corners, a fractionally quantized angular momentum of disclinations, rotationally symmetric fractional charge polarization and its angular momentum counterpart, constraints on charge and angular momentum per unit cell, and quantized momentum bound to dislocations and units of area. The fractionally quantized charge polarization, which is nontrivial only on a lattice with two, three, and fourfold rotation symmetry, implies a fractional charge bound to lattice dislocations and a fractional charge per unit length along the boundary. An important role is played by a finite group grading on Burgers vectors, which depends on the point group symmetry of the lattice.}, doi = {10.1103/PhysRevResearch.3.013040}, author = {Manjunath, Naren and Barkeshli, Maissam} } @article { WOS:000691406500003, title = {Demonstration of Shor Encoding on a Trapped-Ion Quantum Computer}, journal = {Phys. Rev. Appl.}, volume = {16}, number = {2}, year = {2021}, month = {AUG 30}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Fault-tolerant quantum error correction (QEC) is crucial for unlocking the true power of quantum computers. QEC codes use multiple physical qubits to encode a logical qubit, which is protected against errors at the physical qubit level. Here, we use a trapped-ion system to experimentally prepare m-qubit Greenberger-Horne-Zeilinger states and sample the measurement results to construct m x m logical states of the {[}{[}m(2), 1, m]] Shor code, up to m = 7. The synthetic logical fidelity shows how deeper encoding can compensate for additional gate errors in state preparation for larger logical states. However, the optimal code size depends on the physical error rate and we find that m = 5 has the best performance in our system. We further realize the direct logical encoding of the {[}{[}9, 1, 3]] Shor code on nine qubits in a 13-ion chain for comparison, with 98.8(1)\% and 98.5(1)\% fidelity for state vertical bar +/->(L), respectively.}, issn = {2331-7019}, doi = {10.1103/PhysRevApplied.16.024057}, author = {Nguyen, Nhung H. and Li, Muyuan and Green, Alaina M. and Alderete, C. Huerta and Zhu, Yingyue and Zhu, Daiwei and Brown, Kenneth R. and Linke, Norbert M.} } @article { WOS:000670696600015, title = {Deterministic generation of multidimensional photonic cluster states using time-delay feedback}, journal = {Phys. Rev. A}, volume = {104}, number = {1}, year = {2021}, month = {JUL 6}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Cluster states are useful in many quantum information processing applications. In particular, universal measurement-based quantum computation (MBQC) utilizes two-dimensional cluster states {[}R. Raussendorf and H. J. Briegel, Phys. Rev. Lett. 86, 5188 (2001)] and topologically fault-tolerant MBQC requires cluster states of dimension 3 or higher {[}R. Raussendorf et al., New J. Phys. 9, 199 (2007)]. This work proposes a protocol to deterministically generate multidimensional photonic cluster states using a single atom-cavity system and time-delay feedback. The dimensionality of the cluster state increases linearly with the number of time-delay feedbacks. We first give a diagrammatic derivation of the tensor network states, which is valuable in simulating matrix product states and projected entangled pair states generated from sequential photons. Our method also provides a simple way to bridge and analyze the experimental imperfections and the logical errors of the generated states. In this method, we analyze the generated cluster states under realistic experimental conditions and address both one-qubit and two-qubit errors. Through numerical simulation, we observe an optimal atom-cavity cooperativity for the fidelity of the generated states, which is surprising given the prevailing assumption that higher-cooperativity systems are inherently better for photonic applications.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.104.013703}, author = {Shi, Yu and Waks, Edo} } @article { WOS:000674685900002, title = {Development of Quantum Interconnects (QuICs) for Next-Generation Information Technologies}, journal = {PRX Quantum}, volume = {2}, number = {1}, year = {2021}, month = {FEB 24}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Just as {\textquoteleft}{\textquoteleft}classical{{\textquoteright}{\textquoteright}} information technology rests on a foundation built of interconnected information-processing systems, quantum information technology (QIT) must do the same. A critical component of such systems is the {\textquoteleft}{\textquoteleft}interconnect,{{\textquoteright}{\textquoteright}} a device or process that allows transfer of information between disparate physical media, for example, semiconductor electronics, individual atoms, light pulses in optical fiber, or microwave fields. While interconnects have been well engineered for decades in the realm of classical information technology, quantum interconnects (QuICs) present special challenges, as they must allow the transfer of fragile quantum states between different physical parts or degrees of freedom of the system. The diversity of QIT platforms (superconducting, atomic, solid-state color center, optical, etc.) that will form a {\textquoteleft}{\textquoteleft}quantum internet{{\textquoteright}{\textquoteright}} poses additional challenges. As quantum systems scale to larger size, the quantum interconnect bottleneck is imminent, and is emerging as a grand challenge for QIT. For these reasons, it is the position of the community represented by participants of the NSF workshop on {\textquoteleft}{\textquoteleft}Quantum Interconnects{{\textquoteright}{\textquoteright}} that accelerating QuIC research is crucial for sustained development of a national quantum science and technology program. Given the diversity of QIT platforms, materials used, applications, and infrastructure required, a convergent research program including partnership between academia, industry, and national laboratories is required.}, doi = {10.1103/PRXQuantum.2.017002}, author = {Awschalom, David and Berggren, Karl K. and Bernien, Hannes and Bhave, Sunil and Carr, Lincoln D. and Davids, Paul and Economou, Sophia E. and Englund, Dirk and Faraon, Andrei and Fejer, Martin and Guha, Saikat and Gustafsson, V, Martin and Hu, Evelyn and Jiang, Liang and Kim, Jungsang and Korzh, Boris and Kumar, Prem and Kwiat, Paul G. and Loncar, Marko and Lukin, Mikhail D. and Miller, David A. B. and Monroe, Christopher and Nam, Sae Woo and Narang, Prineha and Orcutt, Jason S. and Raymer, Michael G. and Safavi-Naeini, Amir H. and Spiropulu, Maria and Srinivasan, Kartik and Sun, Shuo and Vuckovic, Jelena and Waks, Edo and Walsworth, Ronald and Weiner, Andrew M. and Zhang, Zheshen} } @article { WOS:000657127300005, title = {Disorder effects on Majorana zero modes: Kitaev chain versus semiconductor nanowire}, journal = {Phys. Rev. B}, volume = {103}, number = {22}, year = {2021}, month = {JUN 2}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Majorana zero modes in a superconductor-semiconductor nanowire have been extensively studied during the past decade. Disorder remains a serious problem, preventing the definitive observation of topological Majorana bound states. Thus, it is worthwhile to revisit the simple model, the Kitaev chain, and study the effects of weak and strong disorder on the Kitaev chain. By comparing the role of disorder in a Kitaev chain with that in a nanowire, we find that disorder affects both systems but in a nonuniversal manner. In general, disorder has a much stronger effect on the nanowire than the Kitaev chain, particularly for weak to intermediate disorder. For strong disorder, both the Kitaev chain and nanowire manifest random featureless behavior due to universal Anderson localization. Only the vanishing and strong disorder regimes are thus universal, manifesting respectively topological superconductivity and Anderson localization, but the experimentally relevant intermediate disorder regime is nonuniversal with the details dependent on the disorder realization in the system.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.224505}, author = {Pan, Haining and Das Sarma, S.} } @article {morong_disorder-controlled_2021, title = {Disorder-controlled relaxation in a three-dimensional {Hubbard} model quantum simulator}, journal = {Phys. Rev. Res.}, volume = {3}, number = {1}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {jan}, abstract = {Understanding the collective behavior of strongly correlated electrons in materials remains a central problem in many-particle quantum physics. A minimal description of these systems is provided by the disordered Fermi-Hubbard model (DFHM), which incorporates the interplay of motion in a disordered lattice with local interparticle interactions. Despite its minimal elements, many dynamical properties of the DFHM are not well understood, owing to the complexity of systems combining out-of-equilibrium behavior, interactions, and disorder in higher spatial dimensions. Here, we study the relaxation dynamics of doubly occupied lattice sites in the three-dimensional DFHM using interaction-quench measurements on a quantum simulator composed of fermionic atoms confined in an optical lattice. In addition to observing the widely studied effect of disorder inhibiting relaxation, we find that the cooperation between strong interactions and disorder also leads to the emergence of a dynamical regime characterized by disorder-enhanced relaxation. To support these results, we develop an approximate numerical method and a phenomenological model that each capture the essential physics of the decay dynamics. Our results provide a theoretical framework for a previously inaccessible regime of the DFHM and demonstrate the ability of quantum simulators to enable understanding of complex many-body systems through minimal models.}, doi = {10.1103/PhysRevResearch.3.L012009}, author = {Morong, W. and Muleady, S. R. and Kimchi, I and Xu, W. and Nandkishore, R. M. and Rey, A. M. and DeMarco, B.} } @article { WOS:000655903400002, title = {Disorder-induced zero-bias peaks in Majorana nanowires}, journal = {Phys. Rev. B}, volume = {103}, number = {19}, year = {2021}, month = {MAY 28}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Focusing specifically on the recently retracted work by Zhang et al. {[}H. Zhang et al., Nature (London) 556, 74 (2018); Retraction, Nature (London) 591, E30 (2021)] and the related recently available correctly analyzed data from this Delft experiment (H. Zhang et al., arXiv:2101.11456), we discuss the general problem of confirmation bias in experiments verifying various theoretical topological quantization predictions. We show that the Delft Majorana experiment is most likely dominated by disorder, which produces trivial (but quite sharp and large) zero-bias Andreev tunneling peaks with large conductance similar to 2e(2)/h in the theory, closely mimicking the data. Thus, although the corrected Delft data are by far the best tunnel spectroscopy results available in the literature, manifesting large and sharp zero-bias peaks rising above the background with an impressive hard superconducting gap, our theory shows that the most natural explanation for these zero-bias peaks is that they are disorder induced and not topological Majorana modes. It is possible to misinterpret such disorder-induced zero-bias trivial peaks as the apparent Majorana quantization, as was originally done arising from confirmation bias. One characteristic of the disorder-induced trivial peaks is that they manifest little stability as a function of Zeeman field, chemical potential, and tunnel barrier, distinguishing their trivial behavior from the expected topological robustness of non-Abelian Majorana zero modes. We also analyze a more recent nanowire experiment {[}P. Yu et al., Nat. Phys. 17, 482 (2021)] which is known to have a huge amount of disorder, showing that such highly disordered nanowires may produce very small above-background trivial peaks with conductance values similar to 2e(2)/h in a dirty system manifesting very soft superconducting gap with substantial in-gap conduction, as were already reported by several groups almost 10 years ago. Removing disorder and producing cleaner samples through materials quality improvement and better fabrication is the only way for future progress in this field.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.195158}, author = {Das Sarma, Sankar and Pan, Haining} } @article {baldwin_distinct_2021, title = {Distinct critical behaviors from the same state in quantum spin and population dynamics perspectives}, journal = {Phys. Rev. E}, volume = {103}, number = {1}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {jan}, abstract = {There is a deep connection between the ground states of transverse-field spin systems and the late-time distributions of evolving viral populations-within simple models, both are obtained from the principal eigen-vector of the same matrix. However, that vector is the wave-function amplitude in the quantum spin model, whereas it is the probability itself in the population model. We show that this seemingly minor difference has significant consequences: Phase transitions that are discontinuous in the spin system become continuous when viewed through the population perspective, and transitions that are continuous become governed by new critical exponents. We introduce a more general class of models that encompasses both cases and that can be solved exactly in a mean-field limit. Numerical results are also presented for a number of one-dimensional chains with power-law interactions. We see that well-worn spin models of quantum statistical mechanics can contain unexpected new physics and insights when treated as population-dynamical models and beyond, motivating further studies.}, issn = {2470-0045}, doi = {10.1103/PhysRevE.103.012106}, author = {Baldwin, C. L. and Shivam, S. and Sondhi, S. L. and Kardar, M.} } @article {21096, title = {Domain-wall confinement and dynamics in a quantum simulator}, journal = {Nat. Phys.}, year = {2021}, abstract = {Particles subject to confinement experience an attractive potential that increases without bound as they separate. A prominent example is colour confinement in particle physics, in which baryons and mesons are produced by quark confinement. Confinement can also occur in low-energy quantum many-body systems when elementary excitations are confined into bound quasiparticles. Here we report the observation of magnetic domain-wall confinement in interacting spin chains with a trapped-ion quantum simulator. By measuring how correlations spread, we show that confinement can suppress information propagation and thermalization in such many-body systems. We quantitatively determine the excitation energy of domain-wall bound states from the non-equilibrium quench dynamics. We also study the number of domain-wall excitations created for different quench parameters, in a regime that is difficult to model with classical computers. This work demonstrates the capability of quantum simulators for investigating high-energy physics phenomena, such as quark collision and string breaking. Long-range Ising interactions present in one-dimensional spin chains can induce a confining potential between pairs of domain walls, slowing down the thermalization of the system. This has now been observed in a trapped-ion quantum simulator.

}, issn = {1745-2473}, doi = {10.1038/s41567-021-01194-3}, author = {Tan, W. L. and Becker, P. and Liu, F. and Pagano, G. and Collins, K. S. and De, A. and Feng, L. and Kaplan, H. B. and Kyprianidis, A. and Lundgren, R. and Morong, W. and Whitsitt, S. and Gorshkov, A. V. and Monroe, C.} } @article { WOS:000718354400005, title = {Dynamical fragile topology in Floquet crystals}, journal = {Phys. Rev. B}, volume = {104}, number = {18}, year = {2021}, month = {NOV 9}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Although fragile topology has been intensely studied in static crystals in terms of Wannier obstruction, it is not clear how to generalize the concept to dynamical systems. In this work we generalize the concept of fragile topology, and provide a definition of fragile topology for noninteracting Floquet crystals, which we refer to as dynamical fragile topology. In contrast to the static fragile topology defined by Wannier obstruction, dynamical fragile topology is defined for the nontrivial quantum dynamics characterized by the obstruction to static limits (OTSL). Specifically, the OTSL of a Floquet crystal is fragile if and only if it disappears after adding a symmetry-preserving static Hamiltonian in a direct-sum way preserving the relevant gaps (RGs). We further present a concrete 2 + 1D example for dynamical fragile topology, based on a model that is qualitatively the same as the dynamical model with anomalous chiral edge modes in Rudner et al. {[}Phys. Rev. X 3, 031005 (2013)]. The fragile OTSL in the 2 + 1D example exhibits anomalous chiral edge modes for a natural open boundary condition, and does not require any crystalline symmetries besides lattice translations. Our work paves the way to study fragile topology for general quantum dynamics.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.104.L180303}, author = {Yu, Jiabin and Ge, Yang and Das Sarma, Sankar} } @article { WOS:000707028100001, title = {Dynamical symmetry indicators for Floquet crystals}, journal = {Nat. Commun.}, volume = {12}, number = {1}, year = {2021}, month = {OCT 13}, publisher = {NATURE PORTFOLIO}, type = {Article}, abstract = {Various exotic topological phases of Floquet systems have been shown to arise from crystalline symmetries. Yet, a general theory for Floquet topology that is applicable to all crystalline symmetry groups is still in need. In this work, we propose such a theory for (effectively) non-interacting Floquet crystals. We first introduce quotient winding data to classify the dynamics of the Floquet crystals with equivalent symmetry data, and then construct dynamical symmetry indicators (DSIs) to sufficiently indicate the inherently dynamical Floquet crystals. The DSI and quotient winding data, as well as the symmetry data, are all computationally efficient since they only involve a small number of Bloch momenta. We demonstrate the high efficiency by computing all elementary DSI sets for all spinless and spinful plane groups using the mathematical theory of monoid, and find a large number of different nontrivial classifications, which contain both first-order and higher-order 2+1D anomalous Floquet topological phases. Using the framework, we further find a new 3+1D anomalous Floquet second-order topological insulator (AFSOTI) phase with anomalous chiral hinge modes. A general theory for Floquet topology applicable to all crystalline symmetry groups is lacking. Here, the authors propose such a theory for noninteracting Floquet crystals and predict an inversion-protected Floquet higher-order topological phase with anomalous chiral hinge modes.}, doi = {10.1038/s41467-021-26092-3}, author = {Yu, Jiabin and Zhang, Rui-Xing and Song, Zhi-Da} } @article {lu_efficient_2021, title = {Efficient photoinduced second-harmonic generation in silicon nitride photonics}, journal = {Nat. Photonics}, volume = {15}, number = {2}, year = {2021}, note = {Place: HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY Publisher: NATURE RESEARCH Type: Article}, month = {feb}, pages = {131+}, abstract = {Silicon photonics lacks a second-order nonlinear optical (chi((2))) response in general, because the typical constituent materials are centrosymmetric and lack inversion symmetry, which prohibits chi((2)) nonlinear processes such as second-harmonic generation (SHG). Here, we realize high SHG efficiency in silicon photonics by combining a photoinduced effective chi((2)) nonlinearity with resonant enhancement and perfect phase matching. We show a conversion efficiency of (2,500 +/- 100)\% W-1 that is two to four orders of magnitude larger than previous field-induced SHG works. In particular, our devices realize milliwatt-level SHG output powers with up to (22 +/- 1)\% power conversion efficiency. This demonstration is a breakthrough in realizing efficient chi((2)) processes in silicon photonics, and paves the way for further integration of self-referenced frequency combs and optical frequency references.}, issn = {1749-4885}, doi = {10.1038/s41566-020-00708-4}, author = {Lu, Xiyuan and Moille, Gregory and Rao, Ashutosh and Westly, Daron A. and Srinivasan, Kartik} } @article { WOS:000661896800004, title = {Efficient Stabilized Two-Qubit Gates on a Trapped-Ion Quantum Computer}, journal = {Phys. Rev. Lett.}, volume = {126}, number = {22}, year = {2021}, month = {JUN 4}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {In order to scale up quantum processors and achieve a quantum advantage, it is crucial to economize on the power requirement of two-qubit gates, make them robust to drift in experimental parameters, and shorten the gate times. Applicable to all quantum computer architectures whose two-qubit gates rely on phase-space closure, we present here a new gate-optimizing principle according to which negligible amounts of gate fidelity are traded for substantial savings in power, which, in turn, can be traded for substantial increases in gate speed and/or qubit connectivity. As a concrete example, we illustrate the method by constructing optimal pulses for entangling gates on a pair of ions within a trapped-ion chain, one of the leading quantum computing architectures. Our method is direct, noniterative, and linear, and, in some parameter regimes, constructs gate-steering pulses requiring up to an order of magnitude less power than the standard method. Additionally, our method provides increased robustness to mode drift. We verify the new trade-off principle experimentally on our trapped-ion quantum computer.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.126.220503}, author = {Blumel, Reinhold and Grzesiak, Nikodem and Nguyen, Nhung H. and Green, Alaina M. and Li, Ming and Maksymov, Andrii and Linke, Norbert M. and Nam, Yunseong} } @article { WOS:000684305000006, title = {Electron-boson-interaction induced particle-hole symmetry breaking of conductance into subgap states in superconductors}, journal = {Phys. Rev. Res.}, volume = {3}, number = {3}, year = {2021}, month = {AUG 11}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Particle-hole symmetry (PHS) of conductance into subgap states in superconductors is a fundamental consequence of a noninteracting mean-field theory of superconductivity. The breaking of this PHS has been attributed to a noninteracting mechanism, i.e., quasiparticle poisoning (QP), a process detrimental to the coherence of superconductor-based qubits. Here we show that the ubiquitous electron-boson interactions in superconductors can also break the PHS of subgap conductances. We study the effect of such couplings on the PHS of subgap conductances in superconductors using both the rate equation and Keldysh formalism, which have different regimes of validity. In both regimes, we found that such couplings give rise to a particle-hole asymmetry in subgap conductances which increases with increasing coupling strength, increasing subgap-state particle-hole content imbalance and decreasing temperature. Our proposed mechanism is general and applies even for experiments where the subgap-conductance PHS breaking cannot be attributed to QP.}, doi = {10.1103/PhysRevResearch.3.L032038}, author = {Setiawan, F. and Sau, Jay D.} } @article { WOS:000721731100001, title = {Emergent Replica Conformal Symmetry in Non-Hermitian SYK2 Chains}, journal = {Quantum}, volume = {5}, year = {2021}, month = {NOV 16}, publisher = {VEREIN FORDERUNG OPEN ACCESS PUBLIZIERENS QUANTENWISSENSCHAF}, type = {Article}, abstract = {Recently, the steady states of non-unitary free fermion dynamics are found to exhibit novel critical phases with power-law squared correlations and a logarithmic subsystem entanglement. In this work, we theoretically understand the underlying physics by constructing solvable static/Brownian quadratic Sachdev-YeKitaev chains with non-Hermitian dynamics. We find the action of the replicated system generally shows (one or infinite copies of) O(2) x O(2) symmetries, which is broken to O(2) by the saddle-point solution. This leads to an emergent conformal field theory of the Goldstone modes. We derive the effective action and obtain the universal critical behaviors of squared correlators. Furthermore, the entanglement entropy of a subsystem A with length L-A corresponds to the energy of the half-vortex pair S similar to rho(s) log L-A, where rho(s) is the total stiffness of the Goldstone modes. We also discuss special limits with more than one branch of Goldstone modes and comment on interaction effects.}, issn = {2521-327X}, author = {Zhang, Pengfei and Jian, Shao-Kai and Liu, Chunxiao and Chen, Xiao} } @article { WOS:000679983800006, title = {Energy storage and coherence in closed and open quantum batteries}, journal = {Quantum}, volume = {5}, year = {2021}, month = {JUL 15}, publisher = {VEREIN FORDERUNG OPEN ACCESS PUBLIZIERENS QUANTENWISSENSCHAF}, type = {Article}, abstract = {We study the role of coherence in closed and open quantum batteries. We obtain upper bounds to the work performed or energy exchanged by both closed and open quantum batteries in terms of coherence. Specifically, we show that the energy storage can be bounded by the Hilbert-Schmidt coherence of the density matrix in the spectral basis of the unitary operator that encodes the evolution of the battery. We also show that an analogous bound can be obtained in terms of the battery{\textquoteright}s Hamiltonian coherence in the basis of the unitary operator by evaluating their commutator. We apply these bounds to a 4state quantum system and the anisotropic XY Ising model in the closed system case, and the Spin-Boson model in the open case.}, issn = {2521-327X}, author = {Caravelli, Francesco and Yan, Bin and Garcia-Pintos, Luis Pedro and Hamma, Alioscia} } @article { WOS:000733435400002, title = {Enhancement of superconductivity with external phonon squeezing}, journal = {Phys. Rev. B}, volume = {104}, number = {22}, year = {2021}, month = {DEC 1}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Squeezing of phonons due to the nonlinear coupling to electrons is a way to enhance superconductivity as theoretically studied in a recent work {[}Kennes et al., Nat. Phys. 13, 479 (2017)]. We study quadratic electronphonon interaction in the presence of phonon pumping and an additional external squeezing. Interference between these two driving sources induces a phase-sensitive enhancement of electron-electron attraction, which we find as a generic mechanism to enhance any boson-mediated interactions. The strongest enhancement of superconductivity is shown to be on the boundary with the dynamical lattice instabilities caused by driving. We propose several experimental platforms to realize our scheme.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.104.L220503}, author = {Grankin, Andrey and Hafezi, Mohammad and Galitski, Victor M.} } @article {van_regemortel_entanglement_2021, title = {Entanglement {Entropy} {Scaling} {Transition} under {Competing} {Monitoring} {Protocols}}, journal = {Phys. Rev. Lett.}, volume = {126}, number = {12}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {mar}, abstract = {Dissipation generally leads to the decoherence of a quantum state. In contrast, numerous recent proposals have illustrated that dissipation can also be tailored to stabilize many-body entangled quantum states. While the focus of these works has been primarily on engineering the nonequilibrium steady state, we investigate the buildup of entanglement in the quantum trajectories. Specifically, we analyze the competition between two different dissipation channels arising from two incompatible continuous monitoring protocols. The first protocol locks the phase of neighboring sites upon registering a quantum jump, thereby generating a long-range entanglement through the system, while the second destroys the coherence via a dephasing mechanism. By studying the unraveling of stochastic quantum trajectories associated with the continuous monitoring protocols, we present a transition for the scaling of the averaged trajectory entanglement entropies, from critical scaling to area-law behavior. Our work provides an alternative perspective on the measurement-induced phase transition: the measurement can be viewed as monitoring and registering quantum jumps, offering an intriguing extension of these phase transitions through the long-established realm of quantum optics.

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.126.123604}, author = {Van Regemortel, Mathias and Cian, Ze-Pei and Seif, Alireza and Dehghani, Hossein and Hafezi, Mohammad} } @article { WOS:000730855600005, title = {Estimating disorder and its adverse effects in semiconductor Majorana nanowires}, journal = {Phys. Rev. Mater.}, volume = {5}, number = {12}, year = {2021}, month = {DEC 9}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We use the available transport measurements in the literature to develop a dataset for the likely amount of disorder in semiconductor (InAs and InSb) materials which are used in fabricating the superconductor-semiconductor nanowire samples in the experimental search for Majorana zero modes. Using the estimated disorder in direct Majorana simulations, we conclude that the current level of disorder in semiconductor Majorana nanowires is at least an order of magnitude higher than that necessary for the emergence of topological Majorana zero modes. In agreement with existing results, we find that our estimated disorder leads to the occasional emergence of trivial zero modes, which can be post-selected and then further fine-tuned by varying system parameters (e.g., tunnel barrier), leading to trivial zero-bias conductance peaks in tunneling spectroscopy with similar to 2e(2)/h magnitude. Most calculated tunnel spectra in these disordered systems, however, manifest essentially no significant features, which is also consistent with the current experimental status, where zero-bias peaks are found only occasionally in some samples under careful fine-tuning.}, issn = {2475-9953}, doi = {10.1103/PhysRevMaterials.5.124602}, author = {Ahn, Seongjin and Pan, Haining and Woods, Benjamin and Stanescu, Tudor D. and Das Sarma, Sankar} } @article { WOS:000647487800006, title = {Exact analytical treatment of multiqubit noisy dynamics in exchange-coupled semiconductor spin qubits}, journal = {Phys. Rev. B}, volume = {103}, number = {20}, year = {2021}, month = {MAY 3}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Charge noise remains the primary obstacle to the development of quantum information technologies with semiconductor spin qubits. We use an exact analytical calculation to determine the effects of quasistatic charge noise on a ring of three equally spaced exchange-coupled quantum dots. We calculate the disorder-averaged return probability from a specific initial state and use it to determine the coherence time T-2{*} and show that it depends on only the disorder strength and not the mean interaction strength. We also use a perturbative approach to investigate other arrangements of three or four qubits, finding that the return probability contains multiple oscillation frequencies. These oscillations decay in a Gaussian manner, determined by differences in energy levels of the Hamiltonian. We give quantitative values for gate times resulting in several target fidelities. We find that the decoherence time decreases with an increasing number of qubits. Our work provides useful analytical insight into the charge noise dynamics of coupled spin qubits.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.205402}, author = {Buterakos, Donovan and Das Sarma, Sankar} } @article {zeuner_experimental_2021, title = {Experimental quantum homomorphic encryption}, journal = {npj Quantum Inform.}, volume = {7}, number = {1}, year = {2021}, note = {Place: HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY Publisher: NATURE RESEARCH Type: Article}, month = {feb}, abstract = {Quantum computers promise not only to outperform classical machines for certain important tasks, but also to preserve privacy of computation. For example, the blind quantum computing protocol enables secure delegated quantum computation, where a client can protect the privacy of their data and algorithms from a quantum server assigned to run the computation. However, this security comes with the practical limitation that the client and server must communicate after each step of computation. A practical alternative is homomorphic encryption, which does not require any interactions, while providing quantum-enhanced data security for a variety of computations. In this scenario, the server specifies the computation to be performed, and the client provides only the input data, thus enabling secure noninteractive computation. Here, we demonstrate homomorphic-encrypted quantum computing with unitary transformations of individual qubits, as well as multi-qubit quantum walk computations using single-photon states and non-birefringent integrated optics. The client encrypts their input in the photons{\textquoteright} polarization state, while the server performs the computation using the path degree of freedom. Our demonstration using integrated quantum photonics underlines the applicability of homomorphic-encrypted quantum computations, and shows the potential for delegated quantum computing using photons.}, doi = {10.1038/s41534-020-00340-8}, author = {Zeuner, Jonas and Pitsios, Ioannis and Tan, Si-Hui and Sharma, Aditya N. and Fitzsimons, Joseph F. and Osellame, Roberto and Walther, Philip} } @article {dehghani_extraction_2021, title = {Extraction of the many-body {Chern} number from a single wave function}, journal = {Phys. Rev. B}, volume = {103}, number = {7}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {feb}, abstract = {The quantized Hall conductivity of integer and fractional quantum Hall (IQH and FQH) states is directly related to a topological invariant, the many-body Chern number. The conventional calculation of this invariant in interacting systems requires a family of many-body wave functions parameterized by twist angles to calculate the Berry curvature. In this paper, we demonstrate how to extract the Chern number given a single many-body wave function, without knowledge of the Hamiltonian. For FQH states, our method requires one additional integer invariant as input: the number of 2 pi flux quanta, s, that must be inserted to obtain a topologically trivial excitation. As we discuss, s can be obtained in principle from the degenerate set of ground state wave functions on the torus, without knowledge of the Hamiltonian. We perform extensive numerical simulations involving IQH and FQH states to validate these methods.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.075102}, author = {Dehghani, Hossein and Cian, Ze-Pei and Hafezi, Mohammad and Barkeshli, Maissam} } @article {huang_faithful_2021, title = {Faithful derivation of symmetry indicators: {A} case study for topological superconductors with time-reversal and inversion symmetries}, journal = {Phys. Rev. Res.}, volume = {3}, number = {1}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {mar}, abstract = {Topological crystalline superconductors have attracted rapidly rising attention due to the possibility of higher-order phases, which support Majorana modes on boundaries in d - 2 or lower dimensions. However, although the classification and bulk topological invariants in such systems have been well studied, it is generally difficult to faithfully predict the boundary Majoranas from the band-structure information due to the lack of well-established bulk-boundary correspondence. Here we propose a protocol for deriving symmetry indicators that depend on a minimal set of necessary symmetry data of the bulk bands and can diagnose boundary features. Specifically, to obtain indicators manifesting clear bulk-boundary correspondence, we combine the topological crystal classification scheme in real space and a twisted equivariant K-group analysis in momentum space. The key step is to disentangle the generally mixed strong and weak indicators through a systematic basis-matching procedure between our real-space and momentum-space approaches. We demonstrate our protocol using an example of two-dimensional time-reversal odd-parity superconductors, where the inversion symmetry is known to protect a higher-order phase with corner Majoranas. Symmetry indicators derived from our protocol can be readily applied to an ab initio database and could fuel material predictions for strong and weak topological crystalline superconductors with various boundary features.}, doi = {10.1103/PhysRevResearch.3.013243}, author = {Huang, Sheng-Jie and Hsu, Yi-Ting} } @article { WOS:000648494200001, title = {Fast Logic with Slow Qubits: Microwave-Activated Controlled-Z Gate on Low-Frequency Fluxoniums}, journal = {Phys. Rev. X}, volume = {11}, number = {2}, year = {2021}, month = {MAY 3}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We demonstrate a controlled-Z gate between capacitively coupled fluxonium qubits with transition frequencies 72.3 and 136.3 MHz. The gate is activated by a 61.6-ns-long pulse at a frequency between noncomputational transitions vertical bar 10 > - vertical bar 20 > and vertical bar 11 > - vertical bar 21 >, during which the qubits complete only four and eight Larmor periods, respectively. The measured gate error of (8 +/- 1) x 10(-3) is limited by decoherence in the noncomputational subspace, which will likely improve in the next-generation devices. Although our qubits are about 50 times slower than transmons, the two-qubit gate is faster than microwave-activated gates on transmons, and the gate error is on par with the lowest reported. Architectural advantages of lowfrequency fluxoniums include long qubit coherence time, weak hybridization in the computational subspace, suppressed residual ZZ-coupling rate (here 46 kHz), and the absence of either excessive parameter-matching or complex pulse-shaping requirements.}, issn = {2160-3308}, doi = {10.1103/PhysRevX.11.021026}, author = {Ficheux, Quentin and Nguyen, Long B. and Somoroff, Aaron and Xiong, Haonan and Nesterov, Konstantin N. and Vavilov, Maxim G. and Manucharyan, Vladimir E.} } @article { WOS:000674692700001, title = {Faster Digital Quantum Simulation by Symmetry Protection}, journal = {PRX Quantum}, volume = {2}, number = {1}, year = {2021}, month = {FEB 12}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Simulating the dynamics of quantum systems is an important application of quantum computers and has seen a variety of implementations on current hardware. We show that by introducing quantum gates implementing unitary transformations generated by the symmetries of the system, one can induce destructive interference between the errors from different steps of the simulation, effectively giving faster quantum simulation by symmetry protection. We derive rigorous bounds on the error of a symmetry-protected simulation algorithm and identify conditions for optimal symmetry protection. In particular, when the symmetry transformations are chosen as powers of a unitary, the error of the algorithm is approximately projected to the so-called quantum Zeno subspaces. We prove a bound on this approximation error, exponentially improving a recent result of Burgarth, Facchi, Gramegna, and Pascazio. We apply the symmetry-protection technique to the simulations of the XXZ Heisenberg interactions with local disorder and the Schwinger model in quantum field theory. For both systems, the technique can reduce the simulation error by several orders of magnitude over the unprotected simulation. Finally, we provide numerical evidence suggesting that the technique can also protect simulation against other types of coherent, temporally correlated errors, such as the 1/f noise commonly found in solid-state experiments.}, doi = {10.1103/PRXQuantum.2.010323}, author = {Tran, Minh C. and Su, Yuan and Carney, Daniel and Taylor, Jacob M.} } @article {21316, title = {Fault-tolerant control of an error-corrected qubit}, journal = {Nature}, year = {2021}, abstract = {Quantum error correction protects fragile quantum information by encoding it into a larger quantum system1,2. These extra degrees of freedom enable the detection and correction of errors, but also increase the control complexity of the encoded logical qubit. Fault-tolerant circuits contain the spread of errors while controlling the logical qubit, and are essential for realizing error suppression in practice3,4,5,6. Although fault-tolerant design works in principle, it has not previously been demonstrated in an error-corrected physical system with native noise characteristics. Here we experimentally demonstrate fault-tolerant circuits for the\ preparation, measurement, rotation and stabilizer measurement of a Bacon{\textendash}Shor logical qubit using 13 trapped ion qubits. When we compare these fault-tolerant protocols to non-fault-tolerant protocols, we see significant reductions in the error rates of the logical primitives in the presence of noise. The result of fault-tolerant design is an average state preparation and measurement error of 0.6\ per cent and a Clifford gate error of 0.3\ per cent after offline error correction. In addition, we prepare magic states with fidelities that exceed the distillation threshold7, demonstrating all of the key single-qubit ingredients required for universal fault-tolerant control. These results demonstrate that fault-tolerant circuits enable highly accurate logical primitives in current quantum systems. With improved two-qubit gates and the use of intermediate measurements, a stabilized logical qubit can be achieved.

}, keywords = {error correction, Ion trap, quantum computing}, doi = {10.1038/s41586-021-03928-y}, url = {https://doi.org/10.1038/s41586-021-03928-y}, author = {Laird Egan and Dripto M. Debroy and Crystal Noel and Andrew Risinger and Daiwei Zhu and Debopriyo Biswas and Michael Newman and Muyuan Li and Kenneth R. Brown and Marko Cetina and Christopher Monroe} } @article { WOS:000712467500001, title = {Feedback-stabilized dynamical steady states in the Bose-Hubbard model}, journal = {Phys. Rev. Res.}, volume = {3}, number = {4}, year = {2021}, month = {OCT 27}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The implementation of a combination of continuous weak measurement and classical feedback provides a powerful tool for controlling the evolution of quantum systems. In this paper, we investigate the potential of this approach from three perspectives. First, we consider a double-well system in the classical large-atom-number limit, deriving the exact equations of motion in the presence of feedback. Second, we consider the same system in the limit of small atom number, revealing the effect that quantum fluctuations have on the feedback scheme. Finally, we explore the behavior of modest-sized Hubbard chains using exact numerics, demonstrating the near-deterministic preparation of number states, a tradeoff between local and nonlocal feedback for state preparation, and evidence of a feedback-driven symmetry-breaking phase transition.}, doi = {10.1103/PhysRevResearch.3.043075}, author = {Young, Jeremy T. and Gorshkov, V, Alexey and Spielman, I. B.} } @article { WOS:000704987700003, title = {Fluctuation-dissipation relation for a quantum Brownian oscillator in a parametrically squeezed thermal field}, journal = {Ann. Phys.}, volume = {433}, year = {2021}, month = {OCT}, publisher = {ACADEMIC PRESS INC ELSEVIER SCIENCE}, type = {Article}, abstract = {In this paper we study the nonequilibrium evolution of a quantum Brownian oscillator, modeling the internal degree of freedom of a harmonic atom or an Unruh-DeWitt detector, coupled to a nonequilibrium and nonstationary quantum field bath and inquire whether a fluctuation-dissipation relation (FDR) can exist after/if it approaches equilibration. This is a nontrivial issue because a squeezed field bath cannot reach equilibration and yet, as this work shows, the system oscillator indeed can, which is a necessary condition for FDRs. We discuss three different settings: (A) The bath field essentially remains in a squeezed thermal state throughout, whose squeeze parameter is a mode- and time-independent constant. This situation is often encountered in quantum optics and quantum thermodynamics. (B) The bath field is initially in a thermal state, but is subjected to a parametric process leading to mode- and time-dependent squeezing. This scenario is encountered in cosmology and dynamical Casimir effects. The squeezing in the bath in both types of processes will affect the oscillator{\textquoteright}s nonequilibrium evolution. We show that at late times it approaches equilibration and this stationarity condition warrants the existence of a FDR. The trait of squeezing is marked by the oscillator{\textquoteright}s effective equilibrium temperature, and the proportionality factor in the FDR is only related to the stationary component of the noise kernel of the bath field. Setting (C) is more subtle: A finite system-bath coupling strength can set the oscillator in a squeezed state even though the bath field is stationary and does not engage in any parametric process. The squeezing of the system in this case is in general time-dependent but becomes constant when the internal dynamics is fully relaxed. We begin with comments on the broad range of physical processes involving squeezed thermal baths and end with some remarks on the significance of FDRs in capturing the essence of quantum backreaction in nonequilibrium and stochastic systems. (C) 2021 Elsevier Inc. All rights reserved.}, keywords = {Fluctuation-dissipation relation, nonequilibrium field theory, Parametric oscillator, Squeezed thermal field, Strongly interacting Gaussian system, Time-dependent background}, issn = {0003-4916}, doi = {10.1016/j.aop.2021.168594}, author = {Hsiang, Jen-Tsung and Hu, Bei-Lok} } @article { WOS:000704419000003, title = {Fragile versus stable two-dimensional fermionic quasiparticles}, journal = {Phys. Rev. B}, volume = {104}, number = {12}, year = {2021}, month = {SEP 13}, publisher = {AMER PHYSICAL SOC}, type = {Editorial Material}, abstract = {We provide a comprehensive theoretical investigation of the Fermi liquid quasiparticle description in two-dimensional electron gas interacting via the long-range Coulomb interaction by calculating the electron self-energy within the leading-order approximation, which is exact in the high-density limit. We find that the quasiparticle energy is larger than the imaginary part of the self-energy up to very high energies, implying that the basic Landau quasiparticle picture is robust up to far above the Fermi energy. We find, however, that the quasiparticle picture becomes fragile in a small discrete region around a critical wave vector where the quasiparticle spectral function strongly deviates from the expected quasiparticle Lorentzian line shape with a vanishing renormalization factor. We show that such a non-Fermi liquid behavior arises due to the coupling of quasiparticles with the collective plasmon mode. This situation is somewhat intermediate between the one-dimensional interacting electron gas (i.e., Luttinger liquid), where the Landau Fermi liquid theory completely breaks down since only bosonic collective excitations exist, and three-dimensional electron gas, where quasiparticles are well-defined and more stable against interactions than in one and two dimensions. We use a number of complementary definitions for a quasiparticle to examine the interacting spectral function, contrasting two-dimensional and three-dimensional situations critically.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.104.125118}, author = {Ahn, Seongjin and Das Sarma, Sankar} } @article {mueller_single-particle-like_2021, title = {From single-particle-like to interaction-mediated plasmonic resonances in graphene nanoantennas}, journal = {J. Appl. Phys.}, volume = {129}, number = {9}, year = {2021}, note = {Place: 1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA Publisher: AMER INST PHYSICS Type: Article}, month = {mar}, abstract = {Plasmonic nanostructures attract tremendous attention as they confine electromagnetic fields well below the diffraction limit while simultaneously sustaining extreme local field enhancements. To fully exploit these properties, the identification and classification of resonances in such nanostructures is crucial. Recently, a novel figure of merit for resonance classification has been proposed [Muller et al., J. Phys. Chem. C 124, 24331-24343 (2020)] and its applicability was demonstrated mostly to toy model systems. This novel measure, the energy-based plasmonicity index (EPI), characterizes the nature of resonances in molecular nanostructures. The EPI distinguishes between either a single-particle-like or a plasmonic nature of resonances based on the energy space coherence dynamics of the excitation. To advance the further development of this newly established measure, we present here its exemplary application to characterize the resonances of graphene nanoantennas. In particular, we focus on resonances in a doped nanoantenna. The structure is of interest, as a consideration of the electron dynamics in real space might suggest a plasmonic nature of selected resonances in the low doping limit but our analysis reveals the opposite. We find that in the undoped and moderately doped nanoantenna, the EPI classifies all emerging resonances as predominantly single-particle-like, and only after doping the structure heavily, the EPI observes plasmonic response.}, issn = {0021-8979}, doi = {10.1063/5.0038883}, author = {Mueller, Marvin M. and Kosik, Miriam and Pelc, Marta and Bryant, Garnett W. and Ayuela, Andres and Rockstuhl, Carsten and Slowik, Karolina} } @article { WOS:000693643600008, title = {Frustration-induced anomalous transport and strong photon decay in waveguide QED}, journal = {Phys. Rev. Res.}, volume = {3}, number = {3}, year = {2021}, month = {SEP 7}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study the propagation of photons in a one-dimensional environment consisting of two noninteracting species of photons frustratingly coupled to a single spin 1/2. The ultrastrong frustrated coupling leads to an extreme mixing of the light and matter degrees of freedom, resulting in the disintegration of the spin and a breakdown of the {\textquoteleft}{\textquoteleft}dressed-spin,{{\textquoteright}{\textquoteright}} or polaron, description. Using a combination of numerical and analytical methods, we show that the elastic response becomes increasingly weak at the effective spin frequency, showing instead an increasingly strong and broadband response at higher energies. We also show that the photons can decay into multiple photons of smaller energies. The total probability of these inelastic processes can be as large as the total elastic scattering rate, or half of the total scattering rate, which is as large as it can be. The frustrated spin induces strong anisotropic photon-photon interactions that are dominated by interspecies interactions. Our results are relevant to state-of-the-art circuit and cavity quantum electrodynamics experiments.}, doi = {10.1103/PhysRevResearch.3.L032058}, author = {Belyansky, Ron and Whitsitt, Seth and Lundgren, Rex and Wang, Yidan and Vrajitoarea, Andrei and Houck, Andrew A. and Gorshkov, V, Alexey} } @article { WOS:000655905200002, title = {Generating function for tensor network diagrammatic summation}, journal = {Phys. Rev. B}, volume = {103}, number = {20}, year = {2021}, month = {MAY 28}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The understanding of complex quantum many-body systems has been vastly boosted by tensor network (TN) methods. Among others, excitation spectrum and long-range interacting systems can be studied using TNs, where one however confronts the intricate summation over an extensive number of tensor diagrams. Here, we introduce a set of generating functions, which encode the diagrammatic summations as leading-order series expansion coefficients. Combined with automatic differentiation, the generating function allows us to solve the problem of TN diagrammatic summation. We illustrate this scheme by computing variational excited states and the dynamical structure factor of a quantum spin chain, and further investigating entanglement properties of excited states. Extensions to infinite-size systems and higher dimension are outlined.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.205155}, author = {Tu, Wei-Lin and Wu, Huan-Kuang and Schuch, Norbert and Kawashima, Naoki and Chen, Ji-Yao} } @article { WOS:000674695300001, title = {Geometrical Formalism for Dynamically Corrected Gates in Multiqubit Systems}, journal = {PRX Quantum}, volume = {2}, number = {1}, year = {2021}, month = {MAR 9}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The ability to perform gates in multiqubit systems that are robust to noise is of crucial importance for the advancement of quantum information technologies. However, finding control pulses that cancel noise while performing a gate is made difficult by the intractability of the time-dependent Schrodinger equation, especially in multiqubit systems. Here, we show that this issue can be sidestepped by using a formalism in which the cumulative error during a gate is represented geometrically as a curve in a multidimensional Euclidean space. Cancelation of noise errors to leading order corresponds to closure of the curve, a condition that can be satisfied without solving the Schrodinger equation. We develop and uncover general properties of this geometric formalism, and derive a recursion relation that maps control fields to curvatures for Hamiltonians of arbitrary dimension. We demonstrate the utility of the formalism by employing it to design pulses that simultaneously correct against both noise errors and crosstalk for two qubits coupled by an Ising interaction. We give examples both of a single-qubit rotation and a two-qubit maximally entangling gate. The results obtained in this example are relevant to both superconducting transmon qubits and semiconductor quantum-dot spin qubits. We propose this geometric formalism as a general technique for pulse-induced error suppression in quantum computing gate operations.}, doi = {10.1103/PRXQuantum.2.010341}, author = {Buterakos, Donovan and Das Sarma, Sankar and Barnes, Edwin} } @article { WOS:000670397700010, title = {High temperature measurements of levitated gold nanospheres derived from gold suspensions}, journal = {J. Quant. Spectrosc. Radiat. Transf.}, volume = {270}, year = {2021}, month = {AUG}, publisher = {PERGAMON-ELSEVIER SCIENCE LTD}, type = {Article}, abstract = {We describe a technique for preparing highly charged Au nanospheres that can be collected in a quadrupole ion trap and heated beyond the melting point of Au, using a laser, without discharging. Au nanospheres are first added to solutions of (NH4)(2)CO3 to prepare stable suspensions. Electrospray emission of these suspensions introduces single Au nanospheres into an ion trap in high vacuum, where their charge and mass can be determined from the effect of discrete discharging on their charge to mass ratio, (q/m). After heat treatment to remove residue, q is stable and the nanosphere temperature T can be estimated by mass loss from Au thermal evaporation. Using this technique, we probe the nanosphere melting behavior across the phase transition at T = 1337 K. Finally, we observe that contaminants in the vacuum, probably C, can have a profound effect on the thermal and optical properties of the Au nanospheres near their melting point. (C) 2021 The Authors. Published by Elsevier Ltd.}, keywords = {Electric field trap, Electrospray, Gold nanoparticles, Laser heating, Levitation, Nanoparticles}, issn = {0022-4073}, doi = {10.1016/j.jqsrt.2021.107645}, author = {Coppock, Joyce and Waxter, Quinn and Hannan, Jose and Klueter, Samuel and Kane, B. E.} } @article {green_how_2021, title = {How to profit from quantum technology without building quantum computers}, journal = {Nat. Rev. Phys.}, volume = {3}, number = {3}, year = {2021}, note = {Place: CAMPUS, 4 CRINAN ST, LONDON, N1 9XW, ENGLAND Publisher: SPRINGERNATURE Type: Editorial Material}, month = {mar}, pages = {150{\textendash}152}, abstract = {There are a number of lower risk opportunities to invest in quantum technologies, other than quantum computers, but to make the most of them both specialist knowledge and market awareness are required.}, doi = {10.1038/s42254-021-00290-w}, author = {Green, Dmitry and Soller, Henning and Oreg, Yuval and Galitski, Victor} } @article {briles_hybrid_2021, title = {Hybrid {InP} and {SiN} integration of an octave-spanning frequency comb}, journal = {APL Phontonics}, volume = {6}, number = {2}, year = {2021}, note = {Place: 1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA Publisher: AMER INST PHYSICS Type: Article}, month = {feb}, abstract = {Implementing optical-frequency combs with integrated photonics will enable wider use of precision timing signals. Here, we explore the generation of an octave-span, Kerr-microresonator frequency comb using hybrid integration of an InP distributed-feedback laser and a SiN photonic-integrated circuit. We demonstrate electrically pumped and fiber-packaged prototype systems, enabled by self-injection locking. This direct integration of a laser and a microresonator circuit without previously used intervening elements, such as optical modulators and isolators, necessitates understanding self-injection-locking dynamics with octave-span Kerr solitons. In particular, system architectures must adjust to the strong coupling of microresonator backscattering and laser-microresonator frequency detuning that we uncover here. Our work illustrates critical considerations toward realizing a self-referenced frequency comb with integrated photonics.}, issn = {2378-0967}, doi = {10.1063/5.0035452}, author = {Briles, Travis C. and Yu, Su-Peng and Chang, Lin and Xiang, Chao and Guo, Joel and Kinghorn, David and Moille, Gregory and Srinivasan, Kartik and Bowers, John E. and Papp, Scott B.} } @article { WOS:000658132700032, title = {Hybridization of circular and rectangular transverse profiles of nanophotonic modes for nonlinear optics}, journal = {Opt. Lett.}, volume = {46}, number = {11}, year = {2021}, month = {JUN 1}, pages = {2682-2685}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {Nanophotonic modes within rectangular cross sections are typically considered to have transverse rectangular field profiles. In this work, we show that, despite the rectangular cross section of most integrated waveguides and microring resonators, there exists considerable hybridization of transverse rectangular modes and transverse circular modes. These hybridized modes can be advantageous in nonlinear wave mixing processes. We use third-harmonic generation as an example to confirm that such a hybridized mode is advantageous in combining reasonable mode overlap and waveguide coupling to a fundamental mode in a silicon nitride microring. Our work illuminates the potential of using transverse circular modes in nanophotonic applications. (C) 2021 Optical Society of America}, issn = {0146-9592}, doi = {10.1364/OL.426043}, author = {Lu, Xiyuan and Jiang, Wei C. and Srinivasan, Kartik} } @article { WOS:000646729500001, title = {Hydrodynamic sound and plasmons in three dimensions}, journal = {Phys. Rev. B}, volume = {103}, number = {15}, year = {2021}, month = {APR 1}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {In a recent paper by Lucas and Das Sarma {[}Phys. Rev. B 97. 115449 (2018)], a solvable model of collective modes in two-dimensional metals was considered in the hydrodynamic regime. In the current work, we generalize the hydrodynamic theory to three-dimensional (3D) metals for which the calculation of sound modes in a strongly coupled quantum Coulomb plasma can be made explicit. The specific theoretical question of interest is how the usual linearly dispersing hydrodynamic sound mode relates to the well-known gapped 3D plasmon collective mode in the presence of long-range Coulomb interaction. We show analytically that both the zero sound in the collisionless regime and the first sound in the hydrodynamic region become massive in three dimensions, acquiring a finite gap because of the long-range Coulomb interaction, while their damping rates become quadratic in momentum. We also discuss other types of long-range potential, where the dispersion of sound modes is modified accordingly. The general result is that the leading-order hydrodynamic sound mode is always given by the leading-order plasmon frequency in the presence of long-range Coulomb interaction, but the next-to-leading-order dispersion corrections differ in hydrodynamic and collisionless regimes.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.155101}, author = {Jian, Shao-Kai and Das Sarma, Sankar} } @article { WOS:000722896900048, title = {Impact of the precursor gas ratio on dispersion engineering of broadband silicon nitride microresonator frequency combs}, journal = {Opt. Lett.}, volume = {46}, number = {23}, year = {2021}, month = {DEC 1}, pages = {5970-5973}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {Microresonator frequency combs, or microcombs, have gained wide appeal for their rich nonlinear physics and wide range of applications. Stoichiometric silicon nitride films grown via low-pressure chemical vapor deposition (LPCVD), in particular, are widely used in chip-integrated Kerr microcombs. Critical to such devices is the ability to control the microresonator dispersion, which has contributions from both material refractive index dispersion and geometric confinement. Here, we show that modifications to the ratio of the gaseous precursors in LPCVD growth have a significant impact on material dispersion and hence the overall microresonator dispersion. In contrast to the many efforts focused on comparisons between Si-rich films and stoichiometric (Si3N4) films, here, we focus on films whose precursor gas ratios should nominally place them in the stoichiometric regime. We further show that microresonator geometric dispersion can be tuned to compensate for changes in the material dispersion. (C) 2021 Optical Society of America.}, issn = {0146-9592}, doi = {10.1364/OL.440907}, author = {Moille, Gregory and Westly, Daron and Simelgor, Gregory and Srinivasan, Kartik} } @article { WOS:000652838500026, title = {Inelastic Scattering of a Photon by a Quantum Phase Slip}, journal = {Phys. Rev. Lett.}, volume = {126}, number = {19}, year = {2021}, month = {MAY 12}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Spontaneous decay of a single photon is a notoriously inefficient process in nature irrespective of the frequency range. We report that a quantum phase-slip fluctuation in high-impedance super-conducting waveguides can split a single incident microwave photon into a large number of lower-energy photons with a near unit probability. The underlying inelastic photon-photon interaction has no analogs in nonlinear optics. Instead, the measured decay rates are explained without adjustable parameters in the framework of a new model of a quantum impurity in a Luttinger liquid. Our result connects circuit quantum electrodynamics to critical phenomena in two-dimensional boundary quantum field theories, important in the physics of strongly correlated systems. The photon lifetime data represent a rare example of verified and useful quantum many-body simulation.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.126.197701}, author = {Kuzmin, R. and Grabon, N. and Mehta, N. and Burshtein, A. and Goldstein, M. and Houzet, M. and Glazman, I, L. and Manucharyan, V. E.} } @article { WOS:000688553600007, title = {Interaction-Driven Filling-Induced Metal-Insulator Transitions in 2D Moire Lattices}, journal = {Phys. Rev. Lett.}, volume = {127}, number = {9}, year = {2021}, month = {AUG 24}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Using a realistic band structure for twisted WSe2 materials, we develop a theory for the interaction-driven correlated insulators to conducting metals transitions through the tuning of the filling factor around commensurate fractional fillings of the moire unit cell in the 2D honeycomb lattice, focusing on the dominant half-filled Mott insulating state, which exists for both long- and short-range interactions. We find metallic states slightly away from half-filling, as have recently been observed experimentally. We discuss the stabilities and the magnetic properties of the resulting insulating and metallic phases, and comment on their experimental signatures. We also discuss the nature of the correlated insulator states at the rational fractional fillings.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.127.096802}, author = {Pan, Haining and Das Sarma, Sankar} } @article { WOS:000723344800001, title = {Intrinsic Entropy of Squeezed Quantum Fields and Nonequilibrium Quantum Dynamics of Cosmological Perturbations}, journal = {Entropy}, volume = {23}, number = {11}, year = {2021}, month = {NOV}, publisher = {MDPI}, type = {Article}, abstract = {Density contrasts in the universe are governed by scalar cosmological perturbations which, when expressed in terms of gauge-invariant variables, contain a classical component from scalar metric perturbations and a quantum component from inflaton field fluctuations. It has long been known that the effect of cosmological expansion on a quantum field amounts to squeezing. Thus, the entropy of cosmological perturbations can be studied by treating them in the framework of squeezed quantum systems. Entropy of a free quantum field is a seemingly simple yet subtle issue. In this paper, different from previous treatments, we tackle this issue with a fully developed nonequilibrium quantum field theory formalism for such systems. We compute the covariance matrix elements of the parametric quantum field and solve for the evolution of the density matrix elements and the Wigner functions, and, from them, derive the von Neumann entropy. We then show explicitly why the entropy for the squeezed yet closed system is zero, but is proportional to the particle number produced upon coarse-graining out the correlation between the particle pairs. We also construct the bridge between our quantum field-theoretic results and those using the probability distribution of classical stochastic fields by earlier authors, preserving some important quantum properties, such as entanglement and coherence, of the quantum field.}, keywords = {cosmological particle creation, cosmological perturbations, entropy generation, nonequilibrium field theory}, doi = {10.3390/e23111544}, author = {Hsiang, Jen-Tsung and Hu, Bei-Lok} } @article { WOS:000652826500009, title = {Intrinsic Time-Reversal-Invariant Topological Superconductivity in Thin Films of Iron-Based Superconductors}, journal = {Phys. Rev. Lett.}, volume = {126}, number = {13}, year = {2021}, month = {MAR 30}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We establish quasi-two-dimensional thin films of iron-based superconductors (FeSCs) as a new hightemperature platform for hosting intrinsic time-reversal-invariant helical topological superconductivity (TSC). Based on the combination of Dirac surface state and bulk extended s-wave pairing, our theory should be directly applicable to a large class of experimentally established FeSCs, opening a new TSC paradigm. In particular, an applied electric field serves as a {\textquoteleft}{\textquoteleft}topological switch{{\textquoteright}{\textquoteright}} for helical Majorana edge modes in FeSC thin films, allowing for an experimentally feasible design of gate-controlled helical Majorana circuits. Applying an in-plane magnetic field drives the helical TSC phase into a higher-order TSC carrying corner-localized Majorana zero modes. Our proposal should enable the experimental realization of helical Majorana fermions.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.126.137001}, author = {Zhang, Rui-Xing and Das Sarma, S.} } @article { WOS:000664665500002, title = {Josephson detection of time-reversal symmetry broken superconductivity in SnTe nanowires}, journal = {npj Quantum Mater.}, volume = {6}, number = {1}, year = {2021}, month = {JUN 18}, publisher = {NATURE RESEARCH}, type = {Article}, abstract = {A Josephson junction (JJ) couples the supercurrent flowing between two weakly linked superconductors to the phase difference between them via a current-phase relation (CPR). While a sinusoidal CPR is expected for conventional junctions with insulating weak links, devices made from some exotic materials may give rise to unconventional CPRs and unusual Josephson effects. In this work, we present such a case: we investigate the proximity-induced superconductivity in SnTe nanowires by incorporating them as weak links in JJs and observe a deviation from the standard CPR. We report on indications of an unexpected breaking of time-reversal symmetry in these devices, detailing the unconventional characteristics that reveal this behavior. These include an asymmetric critical current in the DC Josephson effect, a prominent second harmonic in the AC Josephson effect, and a magnetic diffraction pattern with a minimum in critical current at zero magnetic field. The analysis examines how multiband effects and the experimentally visualized ferroelectric domain walls give rise to this behavior, giving insight into the Josephson effect in materials that possess ferroelectricity and/or multiband superconductivity.}, doi = {10.1038/s41535-021-00359-w}, author = {Trimble, C. J. and Wei, M. T. and Yuan, N. F. Q. and Kalantre, S. S. and Liu, P. and Han, H. -J. and Han, M. -G. and Zhu, Y. and Cha, J. J. and Fu, L. and Williams, J. R.} } @article { WOS:000735454800019, title = {Know the enemy: 2D Fermi liquids}, journal = {Ann. Phys.}, volume = {435}, number = {2, SI}, year = {2021}, month = {DEC}, publisher = {ACADEMIC PRESS INC ELSEVIER SCIENCE}, type = {Article}, abstract = {We describe an analytical theory investigating the regime of validity of the Fermi liquid theory in interacting, via the long-range Coulomb coupling, two-dimensional Fermi systems comparing it with the corresponding 3D systems. We find that the 2D Fermi liquid theory and 2D quasiparticles are robust up to high energies and temperatures of the order of Fermi energy above the Fermi surface, very similar to the corresponding three-dimensional situation. We calculate the phase diagram in the frequency- temperature space separating the collisionless ballistic regime and the collision-dominated hydrodynamic regime for 2D and 3D interacting electron systems. We also provide the temperature corrections up to third order for the renormalized effective mass, and comment on the validity of 2D Wiedemann-Franz law and 2D Kadawoki-Woods relation. (c) 2021 Elsevier Inc. All rights reserved.}, keywords = {Electron self-energy, Fermi liquid, Random phase approximation}, issn = {0003-4916}, doi = {10.1016/j.aop.2021.168495}, author = {Das Sarma, Sankar and Liao, Yunxiang} } @article {han_lattice_2021, title = {Lattice vibration as a knob on exotic quantum criticality}, journal = {Phys. Rev. B}, volume = {103}, number = {1}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {jan}, abstract = {Control of quantum coherence in a many-body system is one of the key issues in modern condensed matter, and conventional wisdom is that lattice vibration is an innate source of decoherence. Much research has been conducted to eliminate lattice effects. Challenging this wisdom, we show that lattice vibration may not be a decoherence source but an impetus of a novel coherent quantum many-body state. We demonstrate the possibility by studying the transverse-field Ising model on a chain with renormalization group and density-matrix renormalization group methods and theoretically discover a stable N = 1 supersymmetric quantum criticality with central charge c = 3/2. Thus, we propose an Ising spin chain with strong spin-lattice coupling as a candidate to observe supersymmetry. Generic precursor conditions of novel quantum criticality are obtained by generalizing the Larkin-Pikin criterion of thermal transitions. Our work provides the perspective that lattice vibration may be a knob for exotic quantum many-body states.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.014435}, author = {Han, SangEun and Lee, Junhyun and Moon, Eun-Gook} } @article {21336, title = {Lieb-Robinson Light Cone for Power-Law Interactions}, journal = {Phys. Rev. Lett.}, volume = {127}, year = {2021}, month = {Oct}, pages = {160401}, abstract = {The Lieb-Robinson theorem states that information propagates with a finite velocity in quantum systems on a lattice with nearest-neighbor interactions. What are the speed limits on information propagation in quantum systems with power-law interactions, which decay as\ 1/rÎ±\ at distance\ r? Here, we present a definitive answer to this question for all exponents\ Î±\>2d\ and all spatial dimensions\ d. Schematically, information takes time at least\ rmin{1,Î±-2d}\ to propagate a distance\ r. As recent state transfer protocols saturate this bound, our work closes a decades-long hunt for optimal Lieb-Robinson bounds on quantum information dynamics with power-law interactions.

}, doi = {10.1103/PhysRevLett.127.160401}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.127.160401}, author = {Tran, Minh C. and Guo, Andrew Y. and Baldwin, Christopher L. and Ehrenberg, Adam and Gorshkov, Alexey V. and Lucas, Andrew} } @article {de_bernardis_light-matter_2021, title = {Light-{Matter} {Interactions} in {Synthetic} {Magnetic} {Fields}: {Landau}-{Photon} {Polaritons}}, journal = {Phys. Rev. Lett.}, volume = {126}, number = {10}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {mar}, abstract = {We study light-matter interactions in two-dimensional photonic systems in the presence of a spatially homogeneous synthetic magnetic field for light. Specifically, we consider one or more two-level emitters located in the bulk region of the lattice, where for increasing magnetic field the photonic modes change from extended plane waves to circulating Landau levels. This change has a drastic effect on the resulting emitter-field dynamics, which becomes intrinsically non-Markovian and chiral, leading to the formation of strongly coupled Landau-photon polaritons. The peculiar dynamical and spectral properties of these quasiparticles can be probed with state-of-the-art photonic lattices in the optical and the microwave domain and may find various applications for the quantum simulation of strongly interacting topological models.

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.126.103603}, author = {De Bernardis, Daniele and Cian, Ze-Pei and Carusotto, Iacopo and Hafezi, Mohammad and Rabl, Peter} } @article {dehghani_light-induced_2021, title = {Light-induced topological superconductivity via {Floquet} interaction engineering}, journal = {Phys. Rev. Res.}, volume = {3}, number = {2}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {apr}, abstract = {We propose a mechanism for light-induced unconventional superconductivity in a two-valley semiconductor with a massive Dirac-type band structure. The superconducting phase results from the out-of-equilibrium excitation of carriers in the presence of Coulomb repulsion and is stabilized by coupling the driven semiconductor to a bosonic or fermionic thermal bath. We consider a circularly polarized light pump and show that by controlling the detuning of the pump frequency relative to the band gap, different types of chiral superconductivity would be induced. The emergence of novel superconducting states, such as the chiral p-wave pairing, results from the Floquet engineering of the interaction. This is realized by modifying the form of the Coulomb interaction by projecting it into the states that are resonant with the pump frequency. We show that the resulting unconventional pairing in our system can host topologically protected chiral bound states. We discuss a promising experimental platform to realize our proposal and detect the signatures of the emergent superconducting state.}, doi = {10.1103/PhysRevResearch.3.023039}, author = {Dehghani, Hossein and Hafezi, Mohammad and Ghaemi, Pouyan} } @article { WOS:000627627700006, title = {Light-Matter Interactions in Synthetic Magnetic Fields: Landau-Photon Polaritons}, journal = {Phys. Rev. Lett.}, volume = {126}, number = {10}, year = {2021}, month = {MAR 10}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study light-matter interactions in two-dimensional photonic systems in the presence of a spatially homogeneous synthetic magnetic field for light. Specifically, we consider one or more two-level emitters located in the bulk region of the lattice, where for increasing magnetic field the photonic modes change from extended plane waves to circulating Landau levels. This change has a drastic effect on the resulting emitter-field dynamics, which becomes intrinsically non-Markovian and chiral, leading to the formation of strongly coupled Landau-photon polaritons. The peculiar dynamical and spectral properties of these quasiparticles can be probed with state-of-the-art photonic lattices in the optical and the microwave domain and may find various applications for the quantum simulation of strongly interacting topological models.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.126.103603}, author = {De Bernardis, Daniele and Cian, Ze-Pei and Carusotto, Iacopo and Hafezi, Mohammad and Rabl, Peter} } @article { WOS:000709549100048, title = {Local Control of Supercurrent Density in Epitaxial Planar Josephson Junctions}, journal = {Nano Lett.}, volume = {21}, number = {19}, year = {2021}, month = {OCT 13}, pages = {8274-8280}, publisher = {AMER CHEMICAL SOC}, type = {Article}, abstract = {The critical current response to an applied out-of- plane magnetic field in a Josephson junction provides insight into the uniformity of its current distribution. In Josephson junctions with semiconducting weak links, the carrier density, and therefore the overall current distribution, can be modified electrostatically via metallic gates. Here, we show local control of the current distribution in an epitaxial Al-InAs Josephson junction equipped with five minigates. We demonstrate that not only can the junction width be electrostatically defined but also the current profile can be locally adjusted to form superconducting quantum interference devices. Our studies show enhanced edge conduction in such long junctions, which can be eliminated by minigates to create a uniform current distribution.}, keywords = {band-bending effects, electrostatic gates, Josephson junction, supercurrent distribution}, issn = {1530-6984}, doi = {10.1021/acs.nanolett.1c02771}, author = {Elfeky, Bassel Heiba and Lotfizadeh, Neda and Schiela, William F. and Strickland, William M. and Dartiailh, Matthieu and Sardashti, Kasra and Hatefipour, Mehdi and Yu, Peng and Pankratova, Natalia and Lee, Hanho and Manucharyan, Vladimir E. and Shabani, Javad} } @article { WOS:000735454800008, title = {Loschmidt echo of far-from-equilibrium fermionic superfluids}, journal = {Ann. Phys.}, volume = {435}, number = {2, SI}, year = {2021}, month = {DEC}, publisher = {ACADEMIC PRESS INC ELSEVIER SCIENCE}, type = {Article}, abstract = {Non-analyticities in the logarithm of the Loschmidt echo, known as dynamical quantum phase transitions {[}DQPTs], are a recently introduced attempt to classify the myriad of possible phenomena which can occur in far from equilibrium closed quantum systems. In this work, we analytically investigate the Loschmidt echo in nonequilibrium s-wave and topological p(x) + ip(y) fermionic superfluids. We find that the presence of non-analyticities in the echo is not invariant under global rotations of the superfluid phase. We remedy this deficiency by introducing a more general notion of a grand canonical Loschmidt echo. Overall, our study shows that DQPTs are not a good indicator for the long time dynamics of an interacting system. In particular, there are no DQPTs to tell apart distinct dynamical phases of quenched BCS superconductors. Nevertheless, they can signal a quench induced change in the topology and also keep track of solitons emerging from unstable stationary states of a BCS superconductor. (C) 2021 Elsevier Inc. All rights reserved.}, issn = {0003-4916}, doi = {10.1016/j.aop.2021.168554}, author = {Rylands, Colin and Yuzbashyan, Emil A. and Gurarie, Victor and Zabalo, Aidan and Galitski, Victor} } @article { WOS:000708940500035, title = {Low power threshold, ultrathin optical limiter based on a nonlinear zone plate}, journal = {Opt. Express}, volume = {29}, number = {21}, year = {2021}, month = {OCT 11}, pages = {33144-33154}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {Ultrathin optical limiters are needed to protect light sensitive components in miniaturized optical systems. However, it has proven challenging to achieve a sufficiently low optical limiting threshold. In this work, we theoretically show that an ultrathin optical limiter with low threshold intensity can be realized using a nonlinear one plate. The zone plate is embedded with nonlinear saturable absorbing materials that allow the device to focus low intensity light, while high intensity light is transmitted as a plane wave without a focal spot. Based on this proposed mechanism, we use the finite-difference time-domain method to computationally design a zone plate embedded with InAs quantum dots as the saturable absorbing material. The device has a thickness of just 0.5 mu m and exhibits good optical limiting behavior with a threshold intensity as low as 0.45 kW/cm(2), which is several orders of magnitude lower than bulk limiter counterparts based on a similar mechanism, and also performs favorably compared to current ultrathin flat-optics-based optical limiters. This design can be optimized for different operating wavelengths and threshold intensities by using different saturable absorbing materials. Additionally, the diameter and focal length of the nonlinear zone plate can be easily adjusted to fit different systems and applications. Due to its flexible design, low power threshold, and ultrathin thickness, this optical limiting concept may be promising for application in miniaturized optical systems. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement}, issn = {1094-4087}, doi = {10.1364/OE.434005}, author = {Zhao, Yuqi and Chalabi, Hamidreza and Waks, Edo} } @article {wayne_low-noise_2021, title = {Low-noise photon counting above 100 x 10(6) counts per second with a high-efficiency reach-through single-photon avalanche diode system}, journal = {Appl. Phys. Lett.}, volume = {118}, number = {13}, year = {2021}, note = {Place: 1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA Publisher: AMER INST PHYSICS Type: Article}, abstract = {We demonstrate a method that allows a high-efficiency single-photon-avalanche diode (SPAD) with a thick absorption region ({\textgreater}10 mu m) to count single photons at rates significantly higher than previously demonstrated. We apply large ({\textgreater}30V) AC bias gates to the SPAD at 1GHz and detect minute avalanches with a discrimination threshold of 5(1) mV by means of radio frequency interferometry. We measure a reduction by a factor of approximate to 500 in the average charge per avalanche when compared to operation in its traditional active-quenching module and a relative increase in {\textgreater}19\% in detection efficiency at 850nm. The reduction in charge strongly suppresses self-heating effects in the diode that can degrade performance at high avalanche rates. We show that the single-photon detection system maintains high efficiency at count rates exceeding 10(8) s(-1).}, issn = {0003-6951}, doi = {10.1063/5.0041984}, author = {Wayne, Michael A. and Bienfang, Joshua C. and Migdall, Alan L.} } @article {seif_machine_2021, title = {Machine learning the thermodynamic arrow of time}, journal = {Nat. Phys.}, volume = {17}, number = {1}, year = {2021}, note = {Place: HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY Publisher: NATURE RESEARCH Type: Article}, month = {jan}, abstract = {The asymmetry in the flow of events that is expressed by the phrase {\textquoteleft}time{\textquoteright}s arrow{\textquoteright} traces back to the second law of thermodynamics. In the microscopic regime, fluctuations prevent us from discerning the direction of time{\textquoteright}s arrow with certainty. Here, we find that a machine learning algorithm that is trained to infer the direction of time{\textquoteright}s arrow identifies entropy production as the relevant physical quantity in its decision-making process. Effectively, the algorithm rediscovers the fluctuation theorem as the underlying thermodynamic principle. Our results indicate that machine learning techniques can be used to study systems that are out of equilibrium, and ultimately to answer open questions and uncover physical principles in thermodynamics. The phrase {\textquoteleft}arrow of time{\textquoteright} refers to the asymmetry in the flow of events. A machine learning algorithm trained to infer its direction identifies entropy production as the relevant underlying physical principle in the decision-making process.}, issn = {1745-2473}, doi = {10.1038/s41567-020-1018-2}, author = {Seif, Alireza and Hafezi, Mohammad and Jarzynski, Christopher} } @article { WOS:000663144400001, title = {Machine-learning enhanced dark soliton detection in Bose-Einstein condensates}, journal = {Mach. Learn.-Sci. Technol.}, volume = {2}, number = {3}, year = {2021}, month = {SEP}, publisher = {IOP PUBLISHING LTD}, type = {Article}, abstract = {Most data in cold-atom experiments comes from images, the analysis of which is limited by our preconceptions of the patterns that could be present in the data. We focus on the well-defined case of detecting dark solitons-appearing as local density depletions in a Bose-Einstein condensate (BEC)-using a methodology that is extensible to the general task of pattern recognition in images of cold atoms. Studying soliton dynamics over a wide range of parameters requires the analysis of large datasets, making the existing human-inspection-based methodology a significant bottleneck. Here we describe an automated classification and positioning system for identifying localized excitations in atomic BECs utilizing deep convolutional neural networks to eliminate the need for human image examination. Furthermore, we openly publish our labeled dataset of dark solitons, the first of its kind, for further machine learning research.}, keywords = {convolutional neural network, dark solitons, machine learning}, doi = {10.1088/2632-2153/abed1e}, author = {Guo, Shangjie and Fritsch, Amilson R. and Greenberg, Craig and Spielman, I. B. and Zwolak, Justyna P.} } @article {mcgehee_magneto-optical_2021, title = {Magneto-optical trapping using planar optics}, journal = {New J. Phys.}, volume = {23}, number = {1}, year = {2021}, note = {Place: TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND Publisher: IOP PUBLISHING LTD Type: Article}, month = {jan}, abstract = {Laser-cooled atoms are a key technology for many calibration-free measurement platforms-including clocks, gyroscopes, and gravimeters-and are a promising system for quantum networking and quantum computing. The optics and vacuum hardware required to prepare these gases are often bulky and not amenable to large-volume manufacturing, limiting the practical realization of devices benefiting from the properties of cold atoms. Planar, lithographically produced optics including photonic integrated circuits, optical metasurfaces (MSs), and gratings offer a pathway to develop chip-scale, manufacturable devices utilizing cold atoms. As a demonstration of this technology, we have realized laser cooling of atomic Rb in a grating-type magneto-optical trap (MOT) using planar optics for beam launching, beam shaping, and polarization control. Efficient use of available light is accomplished using MS-enabled beam shaping, and the performance of the planar optics MOT is competitive with Gaussian-beam illuminated grating MOTs.}, keywords = {laser cooling, metasurfaces, photonic integrated circuits}, issn = {1367-2630}, doi = {10.1088/1367-2630/abdce3}, author = {McGehee, William R. and Zhu, Wenqi and Barker, Daniel S. and Westly, Daron and Yulaev, Alexander and Klimov, Nikolai and Agrawal, Amit and Eckel, Stephen and Aksyuk, Vladimir and McClelland, Jabez J.} } @article {wang_magnetotransport_2021, title = {Magnetotransport in hybrid {InSe}/monolayer graphene on {SiC}}, journal = {Nanotechnology}, volume = {32}, number = {15}, year = {2021}, note = {Place: TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND Publisher: IOP PUBLISHING LTD Type: Article}, month = {apr}, abstract = {The magnetotransport properties of a hybrid InSe/monolayer graphene in a SiC system are systematically studied. Compared to those of its bare graphene counterpart, in InSe/graphene, we can effectively modify the carrier density, mobility, effective mass, and electron-electron (e-e) interactions enhanced by weak disorder. We show that in bare graphene and hybrid InSe/graphene systems, the logarithmic temperature (lnT) dependence of the Hall slope R-H = delta R-xy/delta B = delta rho(xy)/delta B can be used to probe e-e interaction effects at various temperatures even when the measured resistivity does not show a lnT dependence due to strong electron-phonon scattering. Nevertheless, one needs to be certain that the change of R-H is not caused by an increase of the carrier density by checking the magnetic field position of the longitudinal resistivity minimum at different temperatures. Given the current challenges in gating graphene on SiC with a suitable dielectric layer, our results suggest that capping a van der Waals material on graphene is an effective way to modify the electronic properties of monolayer graphene on SiC.

}, keywords = {graphene, Hall effect, InSe, interactions}, issn = {0957-4484}, doi = {10.1088/1361-6528/abd726}, author = {Wang, Chih-Yuan and Lin, Yun-Wu and Chuang, Chiashain and Yang, Cheng-Hsueh and Patel, Dinesh K. and Chen, Sheng-Zong and Yeh, Ching-Chen and Chen, Wei-Chen and Lin, Chia-Chun and Chen, Yi-Hsun and Wang, Wei-Hua and Sankar, Raman and Chou, Fang-Cheng and Kruskopf, Mattias and Elmquist, Randolph E. and Liang, Chi-Te} } @article { WOS:000707419400006, title = {Manipulating atom-number distributions and detecting spatial distributions in lattice-confined spinor gases}, journal = {Phys. Rev. A}, volume = {104}, number = {4}, year = {2021}, month = {OCT 15}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We present an experimental study demonstrating the manipulation of atom-number distributions of spinor gases after nonequilibrium quantum quenches across superfluid to Mott-insulator phase transitions in cubic optical lattices. Our data indicate that atom distributions in individual Mott lobes can be tuned by properly designing quantum quench sequences, which suggests methods of maximizing the fraction of atoms in Mott lobes of even occupation numbers and has applications in attaining different quantum magnetic phases including massively entangled states. Spatial distributions of gases in three-dimensional lattices are derived from the observed number distributions, which reveal complex spatial dynamics during the quantum quenches. Qualitative agreements are also found between our experimental data and numerical simulations based on time-dependent Gutzwiller approximations in two-dimensional systems.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.104.L041304}, author = {Austin, J. O. and Shaw, Z. N. and Chen, Z. and Mahmud, K. W. and Liu, Y.} } @article {cian_many-body_2021, title = {Many-{Body} {Chern} {Number} from {Statistical} {Correlations} of {Randomized} {Measurements}}, journal = {Phys. Rev. Lett.}, volume = {126}, number = {5}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {feb}, abstract = {One of the main topological invariants that characterizes several topologically ordered phases is the many-body Chern number (MBCN). Paradigmatic examples include several fractional quantum Hall phases, which are expected to be realized in different atomic and photonic quantum platforms in the near future. Experimental measurement and numerical computation of this invariant are conventionally based on the linear-response techniques that require having access to a family of states, as a function of an external parameter, which is not suitable for many quantum simulators. Here, we propose an ancilla-free experimental scheme for the measurement of this invariant, without requiring any knowledge of the Hamiltonian. Specifically, we use the statistical correlations of randomized measurements to infer the MBCN of a wave function. Remarkably, our results apply to disklike geometries that are more amenable to current quantum simulator architectures.

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.126.050501}, author = {Cian, Ze-Pei and Dehghani, Hossein and Elben, Andreas and Vermersch, Benoit and Zhu, Guanyu and Barkeshli, Maissam and Zoller, Peter and Hafezi, Mohammad} } @article { WOS:000655878500007, title = {Many-body physics in small systems: Observing the onset and saturation of correlation in linear atomic chains}, journal = {Phys. Rev. B}, volume = {103}, number = {19}, year = {2021}, month = {MAY 20}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The exact study of small systems can guide us toward relevant measures for extracting information about many-body physics as we move to larger and more complex systems capable of quantum information processing or quantum analog simulation. We use exact diagonalization to study many electrons in short one-dimensional atom chains represented by long-range extended Hubbard-like models. We introduce a measure, the single-particle excitation content (SPEC) of an eigenstate and show that the functional dependence of the SPEC on the eigenstate number reveals the nature of the ground state (ordered phases), and the onset and saturation of correlation between the electrons as Coulomb interaction strength increases. We use this SPEC behavior to identify five regimes as interaction is increased: A noninteracting single-particle regime, a regime of perturbative Coulomb interaction in which the SPEC is a nearly universal function of eigenstate number, the onset and saturation of correlation, a regime of fully correlated states in which hopping is a perturbation, and the SPEC is a different universal function of state number and the regime of no hopping. In particular, the behavior of the SPEC shows that when electron-electron correlation plays a minor role, all of the lowest-energy eigenstates are made up primarily of single-particle excitations of the ground state, and as the Coulomb interaction increases, the lowest-energy eigenstates increasingly contain many-particle excitations. In addition, the SPEC highlights a fundamental distinct difference between a noninteracting system and one with minute very weak interactions. Although the SPEC is a quantity that can be calculated for small exactly diagonalizable systems, it guides our intuition for larger systems, suggesting the nature of excitations and their distribution in the spectrum. Thus, this function, such as correlation functions or order parameters, provides us with a window of intuition about the behavior of a physical system.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.195429}, author = {Townsend, Emily and Neuman, Tomas and Debrecht, Alex and Aizpurua, Javier and Bryant, Garnett W.} } @article {21241, title = {Many-body thermodynamics on quantum computers via partition function zeros}, journal = {Science Advances}, volume = {7}, year = {2021}, abstract = {Partition functions are ubiquitous in physics: They are important in determining the thermodynamic properties of many-body systems and in understanding their phase transitions. As shown by Lee and Yang, analytically continuing the partition function to the complex plane allows us to obtain its zeros and thus the entire function. Moreover, the scaling and nature of these zeros can elucidate phase transitions. Here, we show how to find partition function zeros on noisy intermediate-scale trapped-ion quantum computers in a scalable manner, using the XXZ spin chain model as a prototype, and observe their transition from XY-like behavior to Ising-like behavior as a function of the anisotropy. While quantum computers cannot yet scale to the thermodynamic limit, our work provides a pathway to do so as hardware improves, allowing the future calculation of critical phenomena for systems beyond classical computing limits.

}, keywords = {quantum computing}, doi = {10.1126/sciadv.abf2447}, url = {https://advances.sciencemag.org/content/7/34/eabf2447}, author = {Francis, Akhil and Zhu, Daiwei and Huerta Alderete, Cinthia and Johri, Sonika and Xiao, Xiao and Freericks, James K. and Monroe, Christopher and Linke, Norbert M. and Kemper, Alexander F.} } @article {chou_marginally_2021, title = {Marginally localized edges of time-reversal symmetric topological superconductors}, journal = {Phys. Rev. B}, volume = {103}, number = {7}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {feb}, abstract = {We demonstrate that the one-dimensional helical Majorana edges of two-dimensional time-reversal symmetric topological superconductors (class DIII) can become gapless and insulating by a combination of random edge velocity and interaction. Such a gapless insulating edge breaks time-reversal symmetry inhomogeneously, and the local symmetry broken regions can be regarded as static mass potentials or dynamical Ising spins. In both limits, we find that such gapless insulating Majorana edges are generically exponentially localized and trap Majorana zero modes. Interestingly, for a statistically time-reversal symmetric edge (symmetry is broken locally, but the symmetry breaking order parameter is zero on average), the low-energy theory can be mapped to a Dyson model at zero energy, manifesting a diverging density of states and exhibiting marginal localization (i.e., a diverging localization length). Although the ballistic edge state transport is absent, the localized Majorana zero modes reflect the nontrivial topology in the bulk. Experimental signatures are also discussed.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.075120}, author = {Chou, Yang-Zhi and Nandkishore, Rahul M.} } @article { WOS:000704691400003, title = {Measurement-Induced Phase Transition in the Monitored Sachdev-Ye-Kitaev Model}, journal = {Phys. Rev. Lett.}, volume = {127}, number = {14}, year = {2021}, month = {SEP 27}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We construct Brownian Sachdev-Ye-Kitaev (SYK) chains subjected to continuous monitoring and explore possible entanglement phase transitions therein. We analytically derive the effective action in the large-N limit and show that an entanglement transition is caused by the symmetry breaking in the enlarged replica space. In the noninteracting case with SYK2 chains, the model features a continuous O(2) symmetry between two replicas and a transition corresponding to spontaneous breaking of that symmetry upon varying the measurement rate. In the symmetry broken phase at low measurement rate, the emergent replica criticality associated with the Goldstone mode leads to a log-scaling entanglement entropy that can be attributed to the free energy of vortices. In the symmetric phase at higher measurement rate, the entanglement entropy obeys area-law scaling. In the interacting case, the continuous O(2) symmetry is explicitly lowered to a discrete C-4 symmetry, giving rise to volume-law entanglement entropy in the symmetry-broken phase due to the enhanced linear free energy cost of domain walls compared to vortices. The interacting transition is described by C-4 symmetry breaking. We also verify the large-N critical exponents by numerically solving the Schwinger-Dyson equation.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.127.140601}, author = {Jian, Shao-Kai and Liu, Chunxiao and Chen, Xiao and Swingle, Brian and Zhang, Pengfei} } @article {lavasani_measurement-induced_2021, title = {Measurement-induced topological entanglement transitions in symmetric random quantum circuits}, journal = {Nat. Phys.}, volume = {17}, number = {3}, year = {2021}, note = {Place: HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY Publisher: NATURE RESEARCH Type: Article}, month = {mar}, pages = {342+}, abstract = {Random quantum circuits, in which an array of qubits is subjected to a series of randomly chosen unitary operations, have provided key insights into the dynamics of many-body quantum entanglement. Recent work has shown that interleaving the unitary operations with single-qubit measurements can drive a transition between high- and low-entanglement phases. Here we study a class of symmetric random quantum circuits with two competing types of measurement in addition to unitary dynamics. We find a rich phase diagram involving robust symmetry-protected topological, trivial and volume law entangled phases, where the transitions are hidden to expectation values of any operator and are only apparent by averaging the entanglement entropy over quantum trajectories. In the absence of unitary dynamics, we find a purely measurement-induced critical point, which maps exactly to two copies of a classical two-dimensional percolation problem. Numerical simulations indicate that this transition is a tricritical point that splits into two critical lines in the presence of arbitrarily sparse unitary dynamics with an intervening volume law entangled phase. Our results show that measurements alone are sufficient to induce criticality and logarithmic entanglement scaling, and arbitrarily sparse unitary dynamics can be sufficient to stabilize volume law entangled phases in the presence of rapid, yet competing, measurements.}, issn = {1745-2473}, doi = {10.1038/s41567-020-01112-z}, author = {Lavasani, Ali and Alavirad, Yahya and Barkeshli, Maissam} } @article {carney_mechanical_2021, title = {Mechanical quantum sensing in the search for dark matter}, journal = {Quantum Sci. Technol.}, volume = {6}, number = {2}, year = {2021}, note = {Place: TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND Publisher: IOP PUBLISHING LTD Type: Article}, month = {apr}, abstract = {Numerous astrophysical and cosmological observations are best explained by the existence of dark matter, a mass density which interacts only very weakly with visible, baryonic matter. Searching for the extremely weak signals produced by this dark matter strongly motivate the development of new, ultra-sensitive detector technologies. Paradigmatic advances in the control and readout of massive mechanical systems, in both the classical and quantum regimes, have enabled unprecedented levels of sensitivity. In this white paper, we outline recent ideas in the potential use of a range of solid-state mechanical sensing technologies to aid in the search for dark matter in a number of energy scales and with a variety of coupling mechanisms.}, keywords = {dark matter, Optomechanics, quantum sensing, standard quantum limits}, issn = {2058-9565}, doi = {10.1088/2058-9565/abcfcd}, author = {Carney, D. and Krnjaic, G. and Moore, D. C. and Regal, C. A. and Afek, G. and Bhave, S. and Brubaker, B. and Corbitt, T. and Cripe, J. and Crisosto, N. and Geraci, A. and Ghosh, S. and Harris, J. G. E. and Hook, A. and Kolb, E. W. and Kunjummen, J. and Lang, R. F. and Li, T. and Lin, T. and Liu, Z. and Lykken, J. and Magrini, L. and Manley, J. and Matsumoto, N. and Monte, A. and Monteiro, F. and Purdy, T. and Riedel, C. J. and Singh, R. and Singh, S. and Sinha, K. and Taylor, J. M. and Qin, J. and Wilson, D. J. and Zhao, Y.} } @article {ahn_microscopic_2021, title = {Microscopic bath effects on noise spectra in semiconductor quantum dot qubits}, journal = {Phys. Rev. B}, volume = {103}, number = {4}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {jan}, abstract = {When a system is thermally coupled to only a small part of a larger bath, statistical fluctuations of the temperature (more precisely, the internal energy) of this {\textquotedblleft}sub-bath{\textquotedblright} around the mean temperature defined by the larger bath can become significant. We show that these temperature fluctuations generally give rise to 1/f-like noise power spectral density from even a single two-level system. We extend these results to a distribution of fluctuators, finding the corresponding modification to the Dutta-Horn relation. Then we consider the specific situation of charge noise in silicon quantum dot qubits and show that recent experimental data [E. J. Connors et al., Phys. Rev. B 100, 165305 (2019)] can be modeled as arising from as few as two two-level fluctuators, and accounting for sub-bath size improves the quality of the fit.

}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.L041304}, author = {Ahn, Seongjin and Sankar Das Sarma and Kestner, J. P.} } @article {vu_moire_2021, title = {Moire versus {Mott}: {Incommensuration} and {Interaction} in {One}-{Dimensional} {Bichromatic} {Lattices}}, journal = {Phys. Rev. Lett.}, volume = {126}, number = {3}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {jan}, abstract = {Inspired by the rich physics of twisted 2D bilayer moire systems, we study Coulomb interacting systems subjected to two overlapping finite ID lattice potentials of unequal periods through exact numerical diagonalization. Unmatching underlying lattice periods lead to a 1D bichromatic {\textquotedblleft}moire{\textquotedblright} superlattice with a large unit cell and consequently a strongly flattened band, exponentially enhancing the effective dimensionless electron-electron interaction strength and manifesting clear signatures of enhanced Mott gaps at discrete fillings. An important nonperturbative finding is a remarkable fine-tuning effect of the precise lattice commensuration, where slight variations in the relative lattice periods may lead to a suppression of the correlated insulating phase, in qualitative agreement with the observed fragility of the correlated insulating phase in twisted bilayer graphene. Our predictions, which should be directly verifiable in bichromatic optical lattices, establish that the competition between interaction and incommensuration is a key element of the physics of moire superlattices.

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.126.036803}, author = {Vu, DinhDuy and Sankar Das Sarma} } @article {yang_momentum_2021, title = {Momentum space toroidal moment in a photonic metamaterial}, journal = {Nat. Commun.}, volume = {12}, number = {1}, year = {2021}, note = {Place: HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY Publisher: NATURE RESEARCH Type: Article}, month = {mar}, abstract = {Berry curvature, the counterpart of the magnetic field in the momentum space, plays a vital role in the transport of electrons in condensed matter physics. It also lays the foundation for the emerging field of topological physics. In the three-dimensional systems, much attention has been paid to Weyl points, which serve as sources and drains of Berry curvature. Here, we demonstrate a toroidal moment of Berry curvature with flux approaching to in judiciously engineered metamaterials. The Berry curvature exhibits a vortex-like configuration without any source and drain in the momentum space. Experimentally, the presence of Berry curvature toroid is confirmed by the observation of conical-frustum shaped domain-wall states at the interfaces formed by two metamaterials with opposite toroidal moments. The appearance of toroidal multipolar moments in electrodynamics interrogates the question for their existence in Berry curvature, which can be seen as the {\textquotedblleft}magnetic field{\textquotedblright} in the momentum space. Here, the authors observe 3D vortex distributions in the Berry curvature within a photonic metamaterial.}, issn = {2041-1723}, doi = {10.1038/s41467-021-22063-w}, author = {Yang, Biao and Bi, Yangang and Zhang, Rui-Xing and Zhang, Ruo-Yang and You, Oubo and Zhu, Zhihong and Feng, Jing and Sun, Hongbo and Chan, C. T. and Liu, Chao-Xing and Zhang, Shuang} } @article { WOS:000654369300091, title = {Multiple-camera defocus imaging of ultracold atomic gases}, journal = {Opt. Express}, volume = {29}, number = {11}, year = {2021}, month = {MAY 24}, pages = {17029-17041}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {In cold atom experiments, each image of light refracted and absorbed by an atomic ensemble carries a remarkable amount of information. Numerous imaging techniques including absorption, fluorescence, and phase-contrast are commonly used. Other techniques such as off-resonance defocused imaging (ORDI, {[}1-4]), where an in-focus image is deconvolved from a defocused image, have been demonstrated but find only niche applications. The ORDI inversion process introduces systematic artifacts because it relies on regularization to account for missing information at some spatial frequencies. In the present work, we extend ORDI to use multiple cameras simultaneously at degrees of defocus, eliminating the need for regularization and its attendant artifacts. We demonstrate this technique by imaging Bose-Einstein condensates, and show that the statistical uncertainties in the measured column density using the multiple-camera off-resonance defocused (McORD) imaging method are competitive with absorption imaging near resonance and phase contrast imaging far from resonance. Experimentally, the McORD method may be incorporated into existing set-ups with minimal additional equipment. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement}, issn = {1094-4087}, doi = {10.1364/OE.422981}, author = {Perry, A. R. and Sugawa, S. and Salces-Carcoba, F. and Yue, Y. and Spielman, I. B.} } @article { WOS:000685620700001, title = {Nanoscale Positioning Approaches for Integrating Single Solid-State Quantum Emitters with Photonic Nanostructures}, journal = {Laser Photon. Rev.}, volume = {15}, number = {10}, year = {2021}, month = {OCT}, publisher = {WILEY-V C H VERLAG GMBH}, type = {Review}, abstract = {Deterministically integrating single solid-state quantum emitters with photonic nanostructures serves as a key enabling resource in the context of photonic quantum technology. Due to the random spatial location of many widely-used solid-state quantum emitters, a number of positioning approaches for locating the quantum emitters before nanofabrication have been explored in the last decade. Here, the working principles of several nanoscale positioning methods and the most recent progress in this field, covering techniques including atomic force microscopy, scanning electron microscopy, confocal microscopy with in situ lithography, and wide-field fluorescence imaging are reviewed. A selection of representative device demonstrations with high-performance is presented, including high-quality single-photon sources, bright entangled-photon pairs, strongly-coupled cavity QED systems, and other emerging applications. The challenges in applying positioning techniques to different material systems and opportunities for using these approaches for realizing large-scale quantum photonic devices are discussed.}, keywords = {deterministic coupling, epitaxial quantum dots, photonic nanostructures}, issn = {1863-8880}, doi = {10.1002/lpor.202100223}, author = {Liu, Shunfa and Srinivasan, Kartik and Liu, Jin} } @article {orek_no_2021, title = {{NO}+ + {H}-2: {Potential} energy surface and bound state calculations}, journal = {Chem. Phys. Lett.}, volume = {771}, year = {2021}, note = {Place: RADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS Publisher: ELSEVIER Type: Article}, abstract = {The first four-dimensional (4D) adiabatic potential energy surface (PES) for the interaction of NO+ cation with the H-2 molecule has been accurately determined using the CCSD(T)-F12a method with cc-pVTZ-F12 basis set augmented with mid-bond functions. A detailed characterization of the PES and lowest bound states of the H-2-NO+ complex have been provided. The H-2-NO+ PES exhibits a single global minimum with a well depth of 824.63 cm(-1) corresponding to off-planar structure with the H-2 molecule in a perpendicular orientation to the NO+ cation. The solution of the nuclear Schrodinger equation for the bound states gives a zero-point energy corrected dissociation energy of D-0 = 498.15 cm(-1) for para-H-2-NO+ complex, and of 541.35 cm(-1) for ortho-H-2-NO+.

}, keywords = {Bound states calculations, Potential energy surface}, issn = {0009-2614}, doi = {10.1016/j.cplett.2021.138511}, author = {Orek, Cahit and Uminski, Marcin and Klos, Jacek and Lique, Francois and Zuchowski, Piotr S. and Bulut, Niyazi} } @article {hsiang_nonequilibrium_2021, title = {Nonequilibrium quantum free energy and effective temperature, generating functional, and influence action}, journal = {Phys. Rev. D}, volume = {103}, number = {6}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {mar}, abstract = {A definition of nonequilibrium free energy F-s is proposed for dynamical Gaussian quantum open systems strongly coupled to a heat bath and the formal relation with the generating functional, the coarse-grained effective action and the influence action is indicated. For Gaussian open quantum systems exemplified by the quantum Brownian motion model studied here, a time-varying effective temperature can be introduced in a natural way, and, with it, the nonequilibrium free energy F-s, von Neumann entropy S-vN and internal energy U-s of the reduced system (S) can be defined accordingly. In contrast to the nonequilibrium free energy found in the literature which references the bath temperature, the nonequilibrium thermodynamic functions we find here obey the familiar relation F-s(t) = U-s(t)-T-EFF(t)S-vN(t) at any and all moments of time in the system{\textquoteright}s fully nonequilibrium evolution history. After the system equilibrates they coincide, in the weak coupling limit, with their counterparts in conventional equilibrium thermodynamics. Since the effective temperature captures both the state of the system and its interaction with the bath, upon the system{\textquoteright}s equilibration, it approaches a value slightly higher than the initial bath temperature. Notably, it remains nonzero for a zero-temperature bath, signaling the existence of system-bath entanglement. Reasonably, at high bath temperatures and under ultraweak couplings, it becomes indistinguishable from the bath temperature. The nonequilibrium thermodynamic functions and relations discovered here for dynamical Gaussian quantum systems should open up useful pathways toward establishing meaningful theories of nonequilibrium quantum thermodynamics.}, issn = {2470-0010}, doi = {10.1103/PhysRevD.103.065001}, author = {Hsiang, Jen-Tsung and Hu, Bei-Lok} } @article { WOS:000723992400001, title = {NonMarkovianity in cosmology: Memories kept in a quantum field}, journal = {Ann. Phys.}, volume = {434}, year = {2021}, month = {NOV}, publisher = {ACADEMIC PRESS INC ELSEVIER SCIENCE}, type = {Article}, abstract = {In this work we ask how an Unruh-DeWitt (UD) detector with harmonic oscillator internal degrees of freedom Q measuring an evolving quantum matter field Phi(x, t) in an expanding universe with scale factor a(t) responds. We investigate the detector{\textquoteright}s response which contains non-Markovian information about the quantum field squeezed by the dynamical spacetime. The challenge is in the memory effects accumulated over the evolutionary history. We first consider a detector W, the {\textquoteleft}Witness{\textquoteright}, which co-existed and evolved with the quantum field from the beginning. We derive a nonMarkovian quantum Langevin equation for the detector{\textquoteright}s Q by integrating over the squeezed quantum field. The solution of this integro-differential equation would answer our question, in principle, but very challenging, in practice. Striking a compromise, we then ask, to what extent can a detector D introduced at late times, called the {\textquoteleft}Detective{\textquoteright}, decipher past memories. This situation corresponds to many cosmological experiments today probing specific stages in the past, such as COBE targeting activities at the surface of last scattering. Somewhat surprisingly we show that it is possible to retrieve to some degree certain global physical quantities, such as the resultant squeezing, particles created, quantum coherence and correlations. The reason is because the quantum field has all the fine-grained information from the beginning in how it was driven by the cosmic dynamics a(t). How long the details of past history can persist in the quantum field depends on the memory time. The fact that a squeezed field cannot come to complete equilibrium under continuous driving, as in an evolving space-time, actually helps to retain the memory. We discuss interesting features and potentials of this {\textquoteleft}archeological{\textquoteright} perspective toward cosmological issues. (C) 2021 Elsevier Inc. All rights reserved.}, keywords = {Nonequilibrium quantum dynamics, NonMarkovianity, Parametric process, Quantum field in a time-dependent background, Quantum memory in cosmological evolution}, issn = {0003-4916}, doi = {10.1016/j.aop.2021.168656}, author = {Hsiang, Jen-Tsung and Hu, Bei-Lok} } @article {jian_note_2021, title = {Note on entropy dynamics in the {Brownian} {SYK} model}, journal = {J. High Energy Phys.}, number = {3}, year = {2021}, note = {Place: ONE NEW YORK PLAZA, SUITE 4600, NEW YORK, NY, UNITED STATES Publisher: SPRINGER Type: Article}, month = {mar}, abstract = {We study the time evolution of Renyi entropy in a system of two coupled Brownian SYK clusters evolving from an initial product state. The Renyi entropy of one cluster grows linearly and then saturates to the coarse grained entropy. This Page curve is obtained by two different methods, a path integral saddle point analysis and an operator dynamics analysis. Using the Brownian character of the dynamics, we derive a master equation which controls the operator dynamics and gives the Page curve for purity. Insight into the physics of this complicated master equation is provided by a complementary path integral method: replica diagonal and non-diagonal saddles are responsible for the linear growth and saturation of Renyi entropy, respectively.}, keywords = {AdS-CFT Correspondence, Black Holes, Nonperturbative Effects, Random Systems}, issn = {1029-8479}, doi = {10.1007/JHEP03(2021)042}, author = {Jian, Shao-Kai and Swingle, Brian} } @article { WOS:000662088000025, title = {Observation of a prethermal discrete time crystal}, journal = {Science}, volume = {372}, number = {6547}, year = {2021}, month = {JUN 11}, pages = {1192+}, publisher = {AMER ASSOC ADVANCEMENT SCIENCE}, type = {Article}, abstract = {Extending the framework of statistical physics to the nonequilibrium setting has led to the discovery of previously unidentified phases of matter, often catalyzed by periodic driving. However, preventing the runaway heating that is associated with driving a strongly interacting quantum system remains a challenge in the investigation of these newly discovered phases. In this work, we utilize a trapped-ion quantum simulator to observe the signatures of a nonequilibrium driven phase without disorder-the prethermal discrete time crystal. Here, the heating problem is circumvented not by disorder-induced many-body localization, but rather by high-frequency driving, which leads to an expansive time window where nonequilibrium phases can emerge. Floquet prethermalization is thus presented as a general strategy for creating, stabilizing, and studying intrinsically out-of-equilibrium phases of matter.}, issn = {0036-8075}, doi = {10.1126/science.abg8102}, author = {Kyprianidis, A. and Machado, F. and Morong, W. and Becker, P. and Collins, K. S. and Else, V, D. and Feng, L. and Hess, P. W. and Nayak, C. and Pagano, G. and Yao, N. Y. and Monroe, C.} } @article {walter_observation_2021, title = {Observation of an {Electric} {Quadrupole} {Transition} in a {Negative} {Ion}: {Experiment} and {Theory}}, journal = {Phys. Rev. Lett.}, volume = {126}, number = {8}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, abstract = {The first direct experimental observation of an electric quadrupole (E2) absorption transition between bound states of an atomic negative ion has been made. The transition was observed in the negative ion of bismuth by resonant (1 + 1) photon detachment from Bi- via P-3(2) -{\textgreater} P-3(0) excitation. The E2 transition properties were completely independently calculated using a hybrid theoretical approach to account for the strong multilevel electron interactions and relativistic effects. The experimental and ab initio theoretical results are in excellent agreement, providing valuable new insight into this complex system and forbidden transitions in negative ions more generally.

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.126.083001}, author = {Walter, C. W. and Spielman, S. E. and Ponce, R. and Gibson, N. D. and Yukich, J. N. and Cheung, C. and Safronova, M. S.} } @article {21526, title = {Observation of {Stark} many-body localization without disorder}, journal = {Nature}, volume = {599}, year = {2021}, pages = {393{\textendash}398}, abstract = {Thermalization is a ubiquitous process of statistical physics, in which a physical system reaches an equilibrium state that is defined by a few global properties such as temperature. Even in isolated quantum many-body systems, limited to reversible dynamics, thermalization typically prevails1. However, in these systems, there is another possibility: many-body localization (MBL) can result in preservation of a non-thermal state2,3. While disorder has long been considered an essential ingredient for this phenomenon, recent theoretical work has suggested that a quantum many-body system with a spatially increasing field{\textemdash}but no disorder{\textemdash}can also exhibit MBL4, resulting in {\textquoteleft}Stark MBL{\textquoteright}5. Here we realize Stark MBL in a trapped-ion quantum simulator and demonstrate its key properties: halting of thermalization and slow propagation of correlations. Tailoring the interactions between ionic spins in an effective field gradient, we directly observe their microscopic equilibration for a variety of initial states, and we apply single-site control to measure correlations between separate regions of the spin chain. Furthermore, by engineering a varying gradient, we create a disorder-free system with coexisting long-lived thermalized and non-thermal regions. The results demonstrate the unexpected generality of MBL, with implications about the fundamental requirements for thermalization and with potential uses in engineering long-lived non-equilibrium quantum matter.

}, issn = {1476-4687}, doi = {10.1038/s41586-021-03988-0}, url = {https://doi.org/10.1038/s41586-021-03988-0}, author = {Morong, W. and Liu, F. and Becker, P. and Collins, K. S. and Feng, L. and Kyprianidis, A. and Pagano, G. and You, T. and Gorshkov, A. V. and Monroe, C.} } @article { WOS:000685113600007, title = {Observation of Vacuum-Induced Collective Quantum Beats}, journal = {Phys. Rev. Lett.}, volume = {127}, number = {7}, year = {2021}, month = {AUG 13}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We demonstrate collectively enhanced vacuum-induced quantum beat dynamics from a three-level V-type atomic system. Exciting a dilute atomic gas of magneto-optically trapped Rb-85 atoms with a weak drive resonant on one of the transitions, we observe the forward-scattered field after a sudden shut-off of the laser. The subsequent radiative dynamics, measured for various optical depths of the atomic cloud, exhibits superradiant decay rates, as well as collectively enhanced quantum beats. Our work is also the first experimental illustration of quantum beats arising from atoms initially prepared in a single excited level as a result of the vacuum-induced coupling between excited levels.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.127.073604}, author = {Han, Hyok Sang and Lee, Ahreum and Sinha, Kanupriya and Fatemi, Fredrik K. and Rolston, S. L.} } @article { WOS:000668996900008, title = {Optical flux pump in the quantum Hall regime}, journal = {Phys. Rev. B}, volume = {103}, number = {24}, year = {2021}, month = {JUN 28}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {A seminal gedankenexperiment by Laughlin describes the charge transport in quantum Hall systems via the pumping of flux. Here, we propose an optical scheme which probes and manipulates quantum Hall systems in a similar way: When light containing orbital angular momentum interacts with electronic Landau levels, it acts as a flux pump which radially moves the electrons through the sample. We investigate this effect for a graphene system with Corbino geometry and calculate the radial current in the absence of any electric potential bias. Remarkably, the current is robust against the disorder which is consistent with the lattice symmetry, and in the weak excitation limit, the current shows a power-law scaling with intensity characterized by the novel exponent 2/3.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.L241301}, author = {Cao, Bin and Grass, Tobias and Solomon, Glenn and Hafezi, Mohammad} } @article { WOS:000665681100001, title = {Optimal calibration of gates in trapped-ion quantum computers}, journal = {Quantum Sci. Technol.}, volume = {6}, number = {3}, year = {2021}, month = {JUL}, publisher = {IOP Publishing Ltd}, type = {Article}, abstract = {To harness the power of quantum computing, it is essential that a quantum computer provide maximal possible fidelity for a quantum circuit. To this end, much work has been done in the context of qubit routing or embedding, i.e., mapping circuit qubits to physical qubits based on gate performance metrics to optimize the fidelity of execution. Here, we take an alternative approach that leverages a unique capability of a trapped-ion quantum computer, i.e., the all-to-all qubit connectivity. We develop a method to determine a fixed number (budget) of quantum gates that, when calibrated, will maximize the fidelity of a batch of input quantum programs. This dynamic allocation of calibration resources on randomly accessible gates, determined using our heuristics, increases, for a wide range of calibration budget, the average fidelity from 70\% or lower to 90\% or higher for a typical batch of jobs on an 11-qubit device, in which the fidelity of calibrated and uncalibrated gates are taken to be 99\% and 90\%, respectively. Our heuristics are scalable, more than 2.5 orders of magnitude faster than a randomized method for synthetic benchmark circuits generated based on real-world use cases.}, keywords = {connectivity, fidelity optimization, gate calibrations}, issn = {2058-9565}, doi = {10.1088/2058-9565/abf718}, author = {Maksymov, Andrii and Niroula, Pradeep and Nam, Yunseong} } @article {19231, title = {Optimal control for quantum detectors}, journal = {npj Quantum Information}, volume = {7}, year = {2021}, month = {03/2021}, abstract = {Quantum systems are promising candidates for sensing of weak signals as they can be highly sensitive to external perturbations, thus providing excellent performance when estimating parameters of external fields. However, when trying to detect weak signals that are hidden by background noise, the signal-to-noise ratio is a more relevant metric than raw sensitivity. We identify, under modest assumptions about the statistical properties of the signal and noise, the optimal quantum control to detect an external signal in the presence of background noise using a quantum sensor. Interestingly, for white background noise, the optimal solution is the simple and well-known spin-locking control scheme. Using numerical techniques, we further generalize these results to the case of background noise with a Lorentzian spectrum. We show that for increasing correlation time, pulse based sequences, such as CPMG, are also close to the optimal control for detecting the signal, with the crossover dependent on the signal frequency. These results show that an optimal detection scheme can be easily implemented in near-term quantum sensors without the need for complicated pulse shaping.

}, doi = {10.1038/s41534-021-00383-5}, url = {https://doi.org/10.1038/s41534-021-00383-5}, author = {Paraj Titum and Kevin Schultz and Alireza Seif and Gregory Quiroz and B. D. Clader} } @article { WOS:000646067200012, title = {Optimal measurement of field properties with quantum sensor networks}, journal = {Phys. Rev. A}, volume = {103}, number = {3}, year = {2021}, month = {MAR 29}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We consider a quantum sensor network of qubit sensors coupled to a field f (x; theta) analytically parameterized by the vector of parameters theta. The qubit sensors are fixed at positions x(1), ..., x(d). While the functional form of f (x; theta) is known, the parameters theta are not. We derive saturable bounds on the precision of measuring an arbitrary analytic function q(theta) of these parameters and construct the optimal protocols that achieve these bounds. Our results are obtained from a combination of techniques from quantum information theory and duality theorems for linear programming. They can be applied to many problems, including optimal placement of quantum sensors, field interpolation, and the measurement of functionals of parametrized fields.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.103.L030601}, author = {Qian, Timothy and Bringewatt, Jacob and Boettcher, Igor and Bienias, Przemyslaw and Gorshkov, V, Alexey} } @article {brady_optimal_2021, title = {Optimal {Protocols} in {Quantum} {Annealing} and {Quantum} {Approximate} {Optimization} {Algorithm} {Problems}}, journal = {Phys. Rev. Lett.}, volume = {126}, number = {7}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {feb}, abstract = {Quantum annealing (QA) and the quantum approximate optimization algorithm (QAOA) are two special cases of the following control problem: apply a combination of two Hamiltonians to minimize the energy of a quantum state. Which is more effective has remained unclear. Here we analytically apply the framework of optimal control theory to show that generically, given a fixed amount of time, the optimal procedure has the pulsed (or {\textquotedblleft}bang-bang{\textquotedblright}) structure of QAOA at the beginning and end but can have a smooth annealing structure in between. This is in contrast to previous works which have suggested that bang-bang (i.e., QAOA) protocols are ideal. To support this theoretical work, we carry out simulations of various transverse field Ising models, demonstrating that bang-anneal-bang protocols are more common. The general features identified here provide guideposts for the nascent experimental implementations of quantum optimization algorithms.

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.126.070505}, author = {Brady, Lucas T. and Baldwin, Christopher L. and Bapat, Aniruddha and Kharkov, Yaroslav and Gorshkov, Alexey V} } @article {21211, title = {Optimal State Transfer and Entanglement Generation in Power-Law Interacting Systems}, journal = {Phys. Rev. X}, volume = {11}, year = {2021}, month = {Jul}, pages = {031016}, abstract = {We present an optimal protocol for encoding an unknown qubit state into a multiqubit Greenberger-Horne-Zeilinger-like state and, consequently, transferring quantum information in large systems exhibiting power-law (1/rÎ±) interactions. For all power-law exponents\ Î±\ between\ d\ and\ 2d+1, where\ d\ is the dimension of the system, the protocol yields a polynomial speed-up for\ Î±\>2d\ and a superpolynomial speed-up for\ Î±<=2d, compared to the state of the art. For all\ Î±\>d, the protocol saturates the Lieb-Robinson bounds (up to subpolynomial corrections), thereby establishing the optimality of the protocol and the tightness of the bounds in this regime. The protocol has a wide range of applications, including in quantum sensing, quantum computing, and preparation of topologically ordered states. In addition, the protocol provides a lower bound on the gate count in digital simulations of power-law interacting systems.

}, keywords = {quantum algorithms, quantum computing}, doi = {10.1103/PhysRevX.11.031016}, url = {https://link.aps.org/doi/10.1103/PhysRevX.11.031016}, author = {Tran, Minh C. and Guo, Andrew Y. and Deshpande, Abhinav and Lucas, Andrew and Gorshkov, Alexey V.} } @article { WOS:000665821600002, title = {Optimal two-qubit circuits for universal fault-tolerant quantum computation}, journal = {npj Quantum Inform.}, volume = {7}, number = {1}, year = {2021}, month = {JUN 22}, publisher = {NATURE RESEARCH}, type = {Article}, abstract = {We study two-qubit circuits over the Clifford+CS gate set, which consists of the Clifford gates together with the controlled-phase gate CS = diag(1, 1, 1, i). The Clifford+CS gate set is universal for quantum computation and its elements can be implemented fault-tolerantly in most error-correcting schemes through magic state distillation. Since non-Clifford gates are typically more expensive to perform in a fault-tolerant manner, it is often desirable to construct circuits that use few CS gates. In the present paper, we introduce an efficient and optimal synthesis algorithm for two-qubit Clifford+CS operators. Our algorithm inputs a Clifford+CS operator U and outputs a Clifford+CS circuit for U, which uses the least possible number of CS gates. Because the algorithm is deterministic, the circuit it associates to a Clifford+CS operator can be viewed as a normal form for that operator. We give an explicit description of these normal forms and use this description to derive a worst-case lower bound of 5log(2)(1/epsilon)+O(1) on the number of CS gates required to epsilon-approximate elements of SU(4). Our work leverages a wide variety of mathematical tools that may find further applications in the study of fault-tolerant quantum circuits.}, doi = {10.1038/s41534-021-00424-z}, author = {Glaudell, Andrew N. and Ross, Neil J. and Taylor, Jacob M.} } @article { WOS:000729420900001, title = {Optimizing Stabilizer Parities for Improved Logical Qubit Memories}, journal = {Phys. Rev. Lett.}, volume = {127}, number = {24}, year = {2021}, month = {DEC 6}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study variants of Shor{\textquoteright}s code that are adept at handling single-axis correlated idling errors, which are commonly observed in many quantum systems. By using the repetition code structure of the Shor{\textquoteright}s code basis states, we calculate the logical channel applied to the encoded information when subjected to coherent and correlated single qubit idling errors, followed by stabilizer measurement. Changing the signs of the stabilizer generators allows us to change how the coherent errors interfere, leading to a quantum error correcting code which performs as well as a classical repetition code of equivalent distance against these errors. We demonstrate a factor of 3.78 +/- 1.20 improvement of the logical T2{*} in a distance-3 logical qubit implemented on a trapped-ion quantum computer. Even-distance versions of our Shor-code variants are decoherence-free subspaces and fully robust to identical and independent coherent idling noise.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.127.240501}, author = {Debroy, Dripto M. and Egan, Laird and Noel, Crystal and Risinger, Andrew and Zhu, Daiwei and Biswas, Debopriyo and Cetina, Marko and Monroe, Chris and Brown, Kenneth R.} } @article {safronova_predicting_2021, title = {Predicting quasibound states of negative ions: {La}- as a test case}, journal = {Phys. Rev. A}, volume = {103}, number = {2}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {feb}, abstract = {We demonstrated the accurate prediction of a quasibound spectrum of a negative ion using a high-precision theoretical approach. We used La as a test case due to a recent experiment that measured energies of 11 resonances in its photodetachment spectrum attributed to transitions to quasibound states [Phys. Rev. A 102, 042812 (2020)]. We identified all of the observed resonances and predicted one more peak just outside the range of the prior experiment. Following the theoretical prediction, the peak was observed at the predicted wavelength, validating the identification. The same approach is applicable to a wide range of negative ions.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.103.022819}, author = {Safronova, M. S. and Cheung, C. and Kozlov, M. G. and Spielman, S. E. and Gibson, N. D. and Walter, C. W.} } @article { WOS:000655905200001, title = {Presence versus absence of two-dimensional Fermi surface anomalies}, journal = {Phys. Rev. B}, volume = {103}, number = {20}, year = {2021}, month = {MAY 28}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We theoretically consider Fermi surface anomalies manifesting in the temperature-dependent quasiparticle properties of two-dimensional (2D) interacting electron systems, comparing and contrasting with the corresponding three-dimensional (3D) Fermi liquid situation. In particular, employing microscopic many-body perturbative techniques, we obtain analytically the leading-order and the next-to-leading-order interaction corrections to the renormalized effective mass for three distinct physical interaction models: electron-phonon, electron-paramagnon, and electron-electron Coulomb coupling. We find that the 2D renormalized effective mass does not develop any Fermi surface anomaly due to electron-phonon interaction, manifesting O(T-2) temperature correction and thus remaining consistent with the Sommerfeld expansion of the noninteracting Fermi function, in contrast to the corresponding 3D situation where the temperature correction to the renormalized effective mass has the anomalous T-2 log T behavior. In contrast, both electron-paramagnon and electron-electron interactions lead to the anomalous O(T) corrections to the 2D effective mass renormalization in contrast to T-2 log T behavior in the corresponding 3D interacting systems. We provide detailed analytical results, and comment on the conditions under which a T-2 log T term could possibly arise in the 2D quasiparticle effective mass from electron-phonon interactions. We also compare results for the temperature-dependent specific heat in the interacting 2D and 3D Fermi systems, using the close connection between the effective mass and specific heat.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.205154}, author = {Buterakos, Donovan and DinhDuy Vu and Yu, Jiabin and Das Sarma, Sankar} } @article { WOS:000646051800005, title = {Probing many-body localization on a noisy quantum computer}, journal = {Phys. Rev. A}, volume = {103}, number = {3}, year = {2021}, month = {MAR 15}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {A disordered quantum system of interacting particles exhibits localized behavior when the disorder is large compared to the interaction strength. Studying this phenomenon on a quantum computer with no, or limited, error correction is challenging because even weak coupling to a thermal environment destroys most signatures of localization. Fortunately, spectral functions of local operators are known to contain features that can survive the presence of noise. In these spectra, discrete peaks and a soft gap at low frequencies compared to the thermal phase indicate localization. Here, we present the computation of spectral functions on a trapped-ion quantum computer for a one-dimensional Heisenberg model with disorder. Further, we design an error-mitigation technique which is effective at removing the noise from the measurement allowing clear signatures of localization to emerge as the disorder increases. Thus, we show that spectral functions can serve as a robust and scalable diagnostic of many-body localization on current and future generations of quantum computers.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.103.032606}, author = {Zhu, D. and Johri, S. and Nguyen, N. H. and Alderete, C. Huerta and Landsman, K. A. and Linke, N. M. and Monroe, C. and Matsuura, A. Y.} } @article { WOS:000705661700006, title = {Probing open- and closed-channel p-wave resonances}, journal = {Phys. Rev. Res.}, volume = {3}, number = {3}, year = {2021}, month = {SEP 20}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study the near-threshold molecular and collisional physics of a strong K-40 p-wave Feshbach resonance through a combination of measurements, numerical calculations, and modeling. Dimer spectroscopy employs both radio-frequency spin-flip association in the MHz band and resonant association in the kHz band. Systematic uncertainty in the measured binding energy is reduced by a model that includes both the Franck-Condon overlap amplitude and inhomogeneous broadening. Coupled-channels calculations based on mass-scaled K-39 potentials compare well to the observed binding energies and also reveal a low-energy p-wave shape resonance in the open channel. Contrary to conventional expectation, we observe a nonlinear variation of the binding energy with magnetic field, and explain how this arises from the interplay of the closed-channel ramping state with the near-threshold shape resonance in the open channel. We develop an analytic two-channel model that includes both resonances as well as the dipole-dipole interactions which, we show, become important at low energy. Using this parametrization of the energy dependence of the scattering phase, we can classify the studied K-40 resonance as broad. Throughout the paper, we compare to the well-understood s-wave case and discuss the significant role played by van der Waals physics. The resulting understanding of the dimer physics of p-wave resonances provides a solid foundation for future exploration of few- and many-body orbital physics.}, doi = {10.1103/PhysRevResearch.3.033269}, author = {Ahmed-Braun, Denise J. M. and Jackson, Kenneth G. and Smale, Scott and Dale, Colin J. and Olsen, Ben A. and Kokkelmans, Servaas J. J. M. F. and Julienne, Paul S. and Thywissen, Joseph H.} } @article { WOS:000655978400001, title = {Programmable quantum simulations of spin systems with trapped ions}, journal = {Rev. Mod. Phys.}, volume = {93}, number = {2}, year = {2021}, month = {APR 7}, publisher = {AMER PHYSICAL SOC}, type = {Review}, abstract = {Laser-cooled and trapped atomic ions form an ideal standard for the simulation of interacting quantum spin models. Effective spins are represented by appropriate internal energy levels within each ion, and the spins can be measured with near-perfect efficiency using state-dependent fluorescence techniques. By applying optical fields that exert optical dipole forces on the ions, their Coulomb interaction can be modulated to produce long-range and tunable spin-spin interactions that can be reconfigured by shaping the spectrum and pattern of the laser fields in a prototypical example of a quantum simulator. Here the theoretical mapping of atomic ions to interacting spin systems, the preparation of complex equilibrium states, and the study of dynamical processes in these many-body interacting quantum systems are reviewed, and the use of this platform for optimization and other tasks is discussed. The use of such quantum simulators for studying spin models may inform our understanding of exotic quantum materials and shed light on the behavior of interacting quantum systems that cannot be modeled with conventional computers.}, issn = {0034-6861}, doi = {10.1103/RevModPhys.93.025001}, author = {Monroe, C. and Campbell, W. C. and Duan, L-M and Gong, Z-X and Gorshkov, V, A. and Hess, P. W. and Islam, R. and Kim, K. and Linke, N. M. and Pagano, G. and Richerme, P. and Senko, C. and Yao, N. Y.} } @article { WOS:000692128200001, title = {Programmable system on chip for controlling an atomic physics experiment}, journal = {Rev. Sci. Instrum.}, volume = {92}, number = {5}, year = {2021}, month = {MAY 1}, publisher = {AIP Publishing}, type = {Article}, abstract = {Most atomic physics experiments are controlled by a digital pattern generator used to synchronize all equipment by providing triggers and clocks. Recently, the availability of well-documented open-source development tools has lifted the barriers to using programmable systems on chip (PSoCs), making them a convenient and versatile tool for synthesizing digital patterns. Here, we take advantage of these advancements in the design of a versatile clock and pattern generator using a PSoC. We present our design with the intent of highlighting the new possibilities that PSoCs have to offer in terms of flexibility. We provide a robust hardware carrier and basic firmware implementation that can be expanded and modified for other uses. Published under license by AIP Publishing.}, issn = {0034-6748}, doi = {10.1063/5.0047535}, author = {Sitaram, A. and Campbell, G. K. and Restelli, A.} } @article { WOS:000674761000001, title = {Proposal for Entangling Gates on Fluxonium Qubits via a Two-Photon Transition}, journal = {PRX Quantum}, volume = {2}, number = {2}, year = {2021}, month = {JUN 22}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We propose a family of microwave-activated entangling gates on two capacitively coupled fluxonium qubits. A microwave pulse applied to either qubit at a frequency near the half-frequency of the vertical bar 00 >-vertical bar 11 > transition induces two-photon Rabi oscillations with a negligible leakage outside the computational subspace, owing to the strong anharmonicity of fluxoniums. By adjusting the drive frequency, amplitude, and duration, we obtain the gate family that is locally equivalent to the fermionic-simulation gates such as root SWAP-like and controlled-phase gates. The gate error can be tuned below 10(-4) for a pulse duration under 100 ns without excessive circuit parameter matching. Given that the fluxonium coherence time can exceed 1 ms, our gate scheme is promising for large-scale quantum processors.}, doi = {10.1103/PRXQuantum.2.020345}, author = {Nesterov, Konstantin N. and Ficheux, Quentin and Manucharyan, Vladimir E. and Vavilov, Maxim G.} } @article {lu_proposal_2021, title = {Proposal for noise-free visible-telecom quantum frequency conversion through third-order sum and difference frequency generation}, journal = {Opt. Lett.}, volume = {46}, number = {2}, year = {2021}, note = {Place: 2010 MASSACHUSETTS AVE NW, WASHINGTON, DC 20036 USA Publisher: OPTICAL SOC AMER Type: Article}, month = {jan}, pages = {222{\textendash}225}, abstract = {Quantum frequency conversion (QFC) between the visible and telecom is a key to connect quantum memories in fiber-based quantum networks. Current methods for linking such widely separated frequencies, such as sum/difference frequency generation and four-wave mixing Bragg scattering, are prone to broadband noise generated by the pump laser(s). To address this issue, we propose to use third-order sum/difference frequency generation (TSFG/TDFG) for an upconversion/downconversion QFC interface. In this process, two long wavelength pump photons combine their energy and momentum to mediate frequency conversion across the large spectral gap between the visible and telecom bands, which is particularly beneficial from the noise perspective. We show that waveguide-coupled silicon nitride microring resonators can be designed for efficient QFC between 606 and 1550 nm via a 1990 nm pump through TSFG/TDFG. We simulate the device dispersion and coupling, and from the simulated parameters, estimate that the frequency conversion can be efficient ({\textgreater}80\%) at 50 mW pump power. Our results suggest that microresonator TSFG/TDFG is promising for compact, scalable, and low-power QFC across large spectral gaps. (C) 2021 Optical Society of America}, issn = {0146-9592}, doi = {10.1364/OL.412602}, author = {Lu, Xiyuan and Moille, Gregory and Rao, Ashutosh and Srinivasan, Kartik} } @article { WOS:000669569500009, title = {Protocols for estimating multiple functions with quantum sensor networks: Geometry and performance}, journal = {Phys. Rev. Res.}, volume = {3}, number = {3}, year = {2021}, month = {JUL 2}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We consider the problem of estimating multiple analytic functions of a set of local parameters via qubit sensors in a quantum sensor network. To address this problem, we highlight a generalization of the sensor symmetric performance bounds of Rubio et al., {[}J. Phys. A 53, 344001 (2020)] and develop an optimized sequential protocol for measuring such functions. We compare the performance of both approaches to one another and to local protocols that do not utilize quantum entanglement, emphasizing the geometric significance of the coefficient vectors of the measured functions in determining the best choice of measurement protocol. We show that, in many cases, especially for a large number of sensors, the optimized sequential protocol results in more accurate measurements than the other strategies. In addition, in contrast to the sensor symmetric approach, the sequential protocol is known to always be explicitly implementable. The sequential protocol is very general and has a wide range of metrological applications.}, doi = {10.1103/PhysRevResearch.3.033011}, author = {Bringewatt, Jacob and Boettcher, Igor and Niroula, Pradeep and Bienias, Przemyslaw and Gorshkov, V, Alexey} } @article { WOS:000662078500026, title = {Purcell-Enhanced Single Photon Source Based on a Deterministically Placed WSe2 Monolayer Quantum Dot in a Circular Bragg Grating Cavity}, journal = {Nano Lett.}, volume = {21}, number = {11}, year = {2021}, month = {JUN 9}, pages = {4715-4720}, publisher = {AMER CHEMICAL SOC}, type = {Article}, abstract = {We demonstrate a deterministic Purcell-enhanced single photon source realized by integrating an atomically thin WSe2 layer with a circular Bragg grating cavity. The cavity significantly enhances the photoluminescence from the atomically thin layer and supports single photon generation with g((2)) (0) < 0.25. We observe a consistent increase of the spontaneous emission rate for WSe2 emitters located in the center of the Bragg grating cavity. These WSe2 emitters are self-aligned and deterministically coupled to such a broadband cavity, configuring a new generation of deterministic single photon sources, characterized by their simple and low-cost production and intrinsic scalability.}, keywords = {bullseyes cavities, Purcell effect, Quantum Dots, single photons, two-dimensional materials}, issn = {1530-6984}, doi = {10.1021/acs.nanolett.1c00978}, author = {Iff, Oliver and Buchinger, Quirin and Moczala-Dusanowska, Magdalena and Kamp, Martin and Betzold, Simon and Davanco, Marcelo and Srinivasan, Kartik and Tongay, Sefaattin and Anton-Solanas, Carlos and Hoefling, Sven and Schneider, Christian} } @article { WOS:000657121500011, title = {Quantized and unquantized zero-bias tunneling conductance peaks in Majorana nanowires: Conductance below and above 2e(2)/h}, journal = {Phys. Rev. B}, volume = {103}, number = {21}, year = {2021}, month = {JUN 1}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Majorana zero modes can appear at the wire ends of a one-dimensional topological superconductor and manifest themselves as a quantized zero-bias conductance peak in the tunneling spectroscopy of normal-superconductor junctions. However, in superconductor-semiconductor hybrid nanowires, zero-bias conductance peaks may arise owing to topologically trivial mechanisms as well, mimicking the Majorana-induced topological peak in many aspects. In this work, we systematically investigate the characteristics of zero-bias conductance peaks for topological Majorana bound states, trivial quasi-Majorana bound states and low-energy Andreev bound states arising from smooth potential variations and disorder-induced subgap bound states. Our focus is on the conductance peak value (i.e., equal to, greater than, or less than 2e(2)/h), as well as the robustness (plateau- or spike-like) against the tuning parameters (e.g., the magnetic field and tunneling gate voltage) for zero-bias peaks arising from the different mechanisms. We find that for Majoranas and quasi-Majoranas, the zero-bias peak values are no more than 2e(2)/h, and a quantized conductance plateau forms generically as a function of parameters. By contrast, for conductance peaks due to low-energy Andreev bound states or disorder-induced bound states, the peak values may exceed 2e(2)/h, and a conductance plateau is rarely observed unless through careful postselection and fine-tuning. Our findings should shed light on the interpretation of experimental measurements on the tunneling spectroscopy of normal-superconductor junctions of hybrid Majorana nanowires.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.214502}, author = {Pan, Haining and Liu, Chun-Xiao and Wimmer, Michael and Das Sarma, Sankar} } @article {niroula_quantum_2021, title = {A quantum algorithm for string matching}, journal = {npj Quantum Inform.}, volume = {7}, number = {1}, year = {2021}, note = {Place: HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY Publisher: NATURE RESEARCH Type: Article}, month = {feb}, abstract = {Algorithms that search for a pattern within a larger data-set appear ubiquitously in text and image processing. Here, we present an explicit, circuit-level implementation of a quantum pattern-matching algorithm that matches a search string (pattern) of length M inside a longer text of length N. Our algorithm has a time complexity of (O) over tilde root N, while the space complexity remains modest at O(N+ M). We report the quantum gate counts relevant for both pre-fault-tolerant and fault-tolerant regimes.}, doi = {10.1038/s41534-021-00369-3}, author = {Niroula, Pradeep and Nam, Yunseong} } @article {norrgard_quantum_2021, title = {Quantum blackbody thermometry}, journal = {New J. Phys.}, volume = {23}, number = {3}, year = {2021}, note = {Place: TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND Publisher: IOP PUBLISHING LTD Type: Article}, month = {mar}, abstract = {Blackbody radiation sources are calculable radiation sources that are frequently used in radiometry, temperature dissemination, and remote sensing. Despite their ubiquity, blackbody sources and radiometers have a plethora of systematics. We envision a new, primary route to measuring blackbody radiation using ensembles of polarizable quantum systems, such as Rydberg atoms and diatomic molecules. Quantum measurements with these exquisite electric field sensors could enable active feedback, improved design, and, ultimately, lower radiometric and thermal uncertainties of blackbody standards. A portable, calibration-free Rydberg-atom physics package could also complement a variety of classical radiation detector and thermometers. The successful merger of quantum and blackbody-based measurements provides a new, fundamental paradigm for blackbody physics.}, keywords = {blackbody radiation, laser cooling molecules, quantum metrology, Rydberg atoms}, issn = {1367-2630}, doi = {10.1088/1367-2630/abe8f5}, author = {Norrgard, Eric B. and Eckel, Stephen P. and Holloway, Christopher L. and Shirley, Eric L.} } @article { WOS:000726704700012, title = {Quantum circuits for the realization of equivalent forms of one-dimensional discrete-time quantum walks on near-term quantum hardware}, journal = {Phys. Rev. A}, volume = {104}, number = {6}, year = {2021}, month = {DEC 1}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Quantum walks are a promising framework for developing quantum algorithms and quantum simulations. They represent an important test case for the application of quantum computers. Here we present different forms of discrete-time quantum walks (DTQWs) and show their equivalence for physical realizations. Using an appropriate digital mapping of the position space on which a walker evolves to the multiqubit states of a quantum processor, we present different configurations of quantum circuits for the implementation of DTQWs in one-dimensional position space. We provide example circuits for a five-qubit processor and address scalability to higher dimensions as well as larger quantum processors.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.104.062401}, author = {Singh, Shivani and Alderete, C. Huerta and Balu, Radhakrishnan and Monroe, Christopher and Linke, Norbert M. and Chandrashekar, C. M.} } @article { WOS:000674685900001, title = {Quantum Computer Systems for Scientific Discovery}, journal = {PRX Quantum}, volume = {2}, number = {1}, year = {2021}, month = {FEB 24}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The great promise of quantum computers comes with the dual challenges of building them and finding their useful applications. We argue that these two challenges should be considered together, by codesigning full-stack quantum computer systems along with their applications in order to hasten their development and potential for scientific discovery. In this context, we identify scientific and community needs, opportunities, a sampling of a few use case studies, and significant challenges for the development of quantum computers for science over the next 2-10 years. This document is written by a community of university, national laboratory, and industrial researchers in the field of Quantum Information Science and Technology, and is based on a summary from a U.S. National Science Foundation workshop on Quantum Computing held on October 21-22, 2019 in Alexandria, VA.}, doi = {10.1103/PRXQuantum.2.017001}, author = {Alexeev, Yuri and Bacon, Dave and Brown, Kenneth R. and Calderbank, Robert and Carr, Lincoln D. and Chong, Frederic T. and DeMarco, Brian and Englund, Dirk and Farhi, Edward and Fefferman, Bill and Gorshkov, V, Alexey and Houck, Andrew and Kim, Jungsang and Kimmel, Shelby and Lange, Michael and Lloyd, Seth and Lukin, Mikhail D. and Maslov, Dmitri and Maunz, Peter and Monroe, Christopher and Preskill, John and Roetteler, Martin and Savage, Martin J. and Thompson, Jeff} } @article {austin_quantum_2021, title = {Quantum critical dynamics in a spinor {Hubbard} model quantum simulator}, journal = {Commun. Phys.}, volume = {4}, number = {1}, year = {2021}, note = {Place: HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY Publisher: NATURE RESEARCH Type: Article}, month = {mar}, abstract = {Three-dimensional (3D) strongly correlated many-body systems, especially their dynamics across quantum phase transitions, are prohibitively difficult to be numerically simulated. We experimentally demonstrate that such complex many-body dynamics can be efficiently studied in a 3D spinor Bose-Hubbard model quantum simulator, consisting of antiferromagnetic spinor Bose-Einstein condensates confined in cubic optical lattices. We find dynamics and scaling effects beyond the scope of existing theories at superfluid-insulator quantum phase transitions, and highlight spin populations as a good observable to probe the quantum critical dynamics. Our data indicate that the scaling exponents are independent of the nature of the quantum phase transitions. We also conduct numerical simulations in lower dimensions using time-dependent Gutzwiller approximations, which qualitatively describe our observations. Three-dimensional (3D) strongly correlated many-body systems and their dynamics across quantum phase transitions pose a challenge when it comes to numerical simulations. The authors experimentally demonstrated that such many-body dynamics can be efficiently studied in a 3D spinor Bose-Hubbard model quantum simulator, and observed dynamics and scaling effects beyond the scope of existing theories at superfluid-insulator quantum phase transitions.}, issn = {2399-3650}, doi = {10.1038/s42005-021-00562-y}, author = {Austin, Jared O. and Chen, Zihe and Shaw, Zachary N. and Mahmud, Khan W. and Liu, Yingmei} } @article { WOS:000734388900001, title = {Quantum Many-Body Topology of Quasicrystals}, journal = {Phys. Rev. X}, volume = {11}, number = {4}, year = {2021}, month = {DEC 14}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {In this paper, we characterize quasicrystalline interacting topological phases of matter, i.e., phases protected by some quasicrystalline structure. We show that the elasticity theory of quasicrystals, which accounts for both {\textquoteleft}{\textquoteleft}phonon{{\textquoteright}{\textquoteright}} and {\textquoteleft}{\textquoteleft}phason{{\textquoteright}{\textquoteright}} modes, admits nontrivial quantized topological terms with far richer structure than their crystalline counterparts. We show that these terms correspond to distinct phases of matter and also uncover intrinsically quasicrystalline phases, which have no crystalline analogs. For quasicrystals with internal U(1) symmetry, we discuss a number of interpretations and physical implications of the topological terms, including constraints on the mobility of dislocations in d = 2 quasicrystals and a quasicrystalline generalization of the Lieb-Schultz-Mattis-Oshikawa-Hastings theorem. We then extend these ideas much further and address the complete classification of quasicrystalline topological phases, including systems with point-group symmetry as well as noninvertible phases. We hence obtain the {\textquoteleft}{\textquoteleft}quasicrystalline equivalence principle,{{\textquoteright}{\textquoteright}} which generalizes the classification of crystalline topological phases to the quasicrystalline setting.}, issn = {2160-3308}, doi = {10.1103/PhysRevX.11.041051}, author = {Else, V, Dominic and Huang, Sheng-Jie and Prem, Abhinav and Gromov, Andrey} } @article { WOS:000643598200024, title = {Quantum Matched Filtering-Signal Processing in the Quantum Age}, journal = {Johns Hopkins APL Tech. Dig.}, volume = {35}, number = {4}, year = {2021}, pages = {422-425}, publisher = {JOHNS HOPKINS UNIV APPLIED PHYSICS LABORATORY LLC}, type = {Article}, abstract = {Optimal quantum control theory identifies the quantum equivalent of a matched filter, which maximizes the signal-to-noise ratio, enabling exploitation of extremely high sensitivity of quantum sensors to detect known signals of interest. This article describes a Johns Hopkins University Applied Physics Laboratory (APL) team{\textquoteright}s work in this field.}, issn = {0270-5214}, author = {Titum, Paraj and Schultz, Kevin M. and Seif, Alireza and Quiroz, Gregory D. and Clader, B. David} } @article { WOS:000691579200002, title = {Quantum routing with fast reversals}, journal = {Quantum}, volume = {5}, year = {2021}, month = {AUG 31}, publisher = {VEREIN FORDERUNG OPEN ACCESS PUBLIZIERENS QUANTENWISSENSCHAF}, type = {Article}, abstract = {We present methods for implementing arbitrary permutations of qubits under interaction constraints. Our protocols make use of previous methods for rapidly reversing the order of qubits along a path. Given nearest-neighbor interactions on a path of length n, we show that there exists a constant epsilon approximate to 0.034 such that the quantum routing time is at most (1 - epsilon)n, whereas any SWAP-based protocol needs at least time n - 1. This represents the first known quantum advantage over SWAP-based routing methods and also gives improved quantum routing times for realistic architectures such as grids. Furthermore, we show that our algorithm approaches a quantum routing time of 2n/3 in expectation for uniformly random permutations, whereas SWAP-based protocols require time n asymptotically. Additionally, we consider sparse permutations that route k <= n qubits and give algorithms with quantum routing time at most n/3 + O(k(2)) on paths and at most 2r/3 + O(k(2)) on general graphs with radius r.}, issn = {2521-327X}, author = {Bapat, Aniruddha and Childs, Andrew M. and V. Gorshkov, Alexey and King, Samuel and Schoute, Eddie and Shastri, Hrishee} } @article { WOS:000674685900003, title = {Quantum Simulators: Architectures and Opportunities}, journal = {PRX Quantum}, volume = {2}, number = {1}, year = {2021}, month = {FEB 24}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Quantum simulators are a promising technology on the spectrum of quantum devices from specialized quantum experiments to universal quantum computers. These quantum devices utilize entanglement and many-particle behavior to explore and solve hard scientific, engineering, and computational problems. Rapid development over the last two decades has produced more than 300 quantum simulators in operation worldwide using a wide variety of experimental platforms. Recent advances in several physical architectures promise a golden age of quantum simulators ranging from highly optimized special purpose simulators to flexible programmable devices. These developments have enabled a convergence of ideas drawn from fundamental physics, computer science, and device engineering. They have strong potential to address problems of societal importance, ranging from understanding vital chemical processes, to enabling the design of new materials with enhanced performance, to solving complex computational problems. It is the position of the community, as represented by participants of the National Science Foundation workshop on {\textquoteleft}{\textquoteleft}Programmable Quantum Simulators,{{\textquoteright}{\textquoteright}} that investment in a national quantum simulator program is a high priority in order to accelerate the progress in this field and to result in the first practical applications of quantum machines. Such a program should address two areas of emphasis: (1) support for creating quantum simulator prototypes usable by the broader scientific community, complementary to the present universal quantum computer effort in industry; and (2) support for fundamental research carried out by a blend of multi-investigator, multidisciplinary collaborations with resources for quantum simulator software, hardware, and education. This document is a summary from a U.S. National Science Foundation supported workshop held on 16-17 September 2019 in Alexandria, VA. Attendees were charged to identify the scientific and community needs, opportunities, and significant challenges for quantum simulators over the next 2-5 years.}, doi = {10.1103/PRXQuantum.2.017003}, author = {Altman, Ehud and Brown, Kenneth R. and Carleo, Giuseppe and Carr, Lincoln D. and Demler, Eugene and Chin, Cheng and DeMarco, Brian and Economou, Sophia E. and Eriksson, Mark A. and Fu, Kai-Mei C. and Greiner, Markus and Hazzard, Kaden R. A. and Hulet, Randall G. and Kollar, Alicia J. and Lev, Benjamin L. and Lukin, Mikhail D. and Ma, Ruichao and Mi, Xiao and Misra, Shashank and Monroe, Christopher and Murch, Kater and Nazario, Zaira and Ni, Kang-Kuen and Potter, Andrew C. and Roushan, Pedram and Saffman, Mark and Schleier-Smith, Monika and Siddiqi, Irfan and Simmonds, Raymond and Singh, Meenakshi and Spielman, I. B. and Temme, Kristan and Weiss, David S. and Vuckovic, Jelena and Vuletic, Vladan and Ye, Jun and Zwierlein, Martin} } @article { WOS:000692200800013, title = {Quantum Spin State Selectivity and Magnetic Tuning of Ultracold Chemical Reactions of Triplet Alkali-Metal Dimers with Alkali-Metal Atoms}, journal = {Phys. Rev. Lett.}, volume = {127}, number = {10}, year = {2021}, month = {AUG 31}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {{We demonstrate that it is possible to efficiently control ultracold chemical reactions of alkali-metal atoms colliding with open-shell alkali-metal dimers in their metastable triplet states by choosing the internal hyperfine and rovibrational states of the reactants as well as by inducing magnetic Feshbach resonances with an external magnetic field. We base these conclusions on coupled-channel statistical calculations that include the effects of hyperfine contact and magnetic-field-induced Zeeman interactions on ultracold chemical reactions of hyperfine-resolved ground-state Na and the triplet NaLi(a(3)Sigma(+)) producing singlet Na-2((1)Sigma(+)(g)) and a Li atom. We find that the reaction rates are sensitive to the initial hyperfine states of the reactants. The chemical reaction of fully spin-polarized, high-spin states of rotationless NaLi(a(3)Sigma(+)}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.127.103402}, author = {Hermsmeier, Rebekah and Klos, Jacek and Kotochigova, Svetlana and Tscherbul, Timur V.} } @article { WOS:000675612700001, title = {Quantum teleportation and entanglement swapping with long baseline in outer space}, journal = {Class. Quantum Gravity}, volume = {38}, number = {16}, year = {2021}, month = {AUG 19}, publisher = {IOP PUBLISHING LTD}, type = {Article}, abstract = {Quantum information (QI) experiments applying quantum optics in outer space with a very long baseline may have advantages over the current Earth-bound experiments or the Earth-to-satellite experiments, because they can minimize the loss in light transmission and maximize the gain in time resolution. This future class of experiments, among them quantum teleportation and entanglement swapping, can shed light on many fundamental theoretical issues in gravitational quantum physics and relativistic QI. Regarding relativity theory, these experiments in an outer-space setting can involve observations at spacelike and timelike separations and explicate intriguing phenomena from different choices of time-slicing. Regarding QI, they may be able to ensure the causal independence of the expectation values in the Bell test. These issues are addressed in this paper with analysis and explanations.}, keywords = {quantum entanglement, quantum teleportation, relativistic quantum information}, issn = {0264-9381}, doi = {10.1088/1361-6382/ac1080}, author = {Lin, Shih-Yuin and Hu, Bei-Lok} } @article { WOS:000655928700001, title = {Quench Dynamics of a Fermi Gas with Strong Nonlocal Interactions}, journal = {Phys. Rev. X}, volume = {11}, number = {2}, year = {2021}, month = {MAY 17}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We induce strong nonlocal interactions in a 2D Fermi gas in an optical lattice using Rydberg dressing. The system is approximately described by a t - V model on a square lattice where the fermions experience isotropic nearest-neighbor interactions and are free to hop only along one direction. We measure the interactions using many-body Ramsey interferometry and study the lifetime of the gas in the presence of tunneling, finding that tunneling does not reduce the lifetime. To probe the interplay of nonlocal interactions with tunneling, we investigate the short-time-relaxation dynamics of charge-density waves in the gas. We find that strong nearest-neighbor interactions slow down the relaxation. Our work opens the door for quantum simulations of systems with strong nonlocal interactions such as extended Fermi-Hubbard models.}, issn = {2160-3308}, doi = {10.1103/PhysRevX.11.021036}, author = {Guardado-Sanchez, Elmer and Spar, Benjamin M. and Schauss, Peter and Belyansky, Ron and Young, Jeremy T. and Bienias, Przemyslaw and Gorshkov, V, Alexey and Iadecola, Thomas and Bakr, Waseem S.} } @article { WOS:000674748200001, title = {Ray-Based Framework for State Identification in Quantum Dot Devices}, journal = {PRX Quantum}, volume = {2}, number = {2}, year = {2021}, month = {JUN 7}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Quantum dots (QDs) defined with electrostatic gates are a leading platform for a scalable quantum computing implementation. However, with increasing numbers of qubits, the complexity of the control parameter space also grows. Traditional measurement techniques, relying on complete or near-complete exploration via two-parameter scans (images) of the device response, quickly become impractical with increasing numbers of gates. Here we propose to circumvent this challenge by introducing a measurement technique relying on one-dimensional projections of the device response in the multidimensional parameter space. Dubbed the {\textquoteleft}{\textquoteleft}ray-based classification (RBC) framework,{{\textquoteright}{\textquoteright}} we use this machine learning approach to implement a classifier for QD states, enabling automated recognition of qubit-relevant parameter regimes. We show that RBC surpasses the 82\% accuracy benchmark from the experimental implementation of image-based classification techniques from prior work, while reducing the number of measurement points needed by up to 70\%. The reduction in measurement cost is a significant gain for time-intensive QD measurements and is a step forward toward the scalability of these devices. We also discuss how the RBC-based optimizer, which tunes the device to a multiqubit regime, performs when tuning in the two-dimensional and three-dimensional parameter spaces defined by plunger and barrier gates that control the QDs. This work provides experimental validation of both efficient state identification and optimization with machine learning techniques for nontraditional measurements in quantum systems with high-dimensional parameter spaces and time-intensive measurements.}, doi = {10.1103/PRXQuantum.2.020335}, author = {Zwolak, Justyna P. and McJunkin, Thomas and Kalantre, Sandesh S. and Neyens, Samuel F. and MacQuarrie, E. R. and Eriksson, Mark A. and Taylor, Jacob M.} } @article { WOS:000704615000003, title = {Real-time quantum calculations of phase shifts using wave packet time delays}, journal = {Phys. Rev. D}, volume = {104}, number = {5}, year = {2021}, month = {SEP 16}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We present a method to extract the phase shift of a scattering process using the real-time evolution in the early and intermediate stages of the collision in order to estimate the time delay of a wave packet. This procedure is convenient when using noisy quantum computers for which the asymptotic out-state behavior is unreachable. We demonstrate that the challenging Fourier transforms involved in the state preparation and measurements can be implemented in 1 + 1 dimensions with current trapped ion devices and IBM quantum computers. We compare quantum computations of the time delays obtained in the one-particle quantum mechanics limit and the scalable quantum field theory formulation with accurate numerical results. We discuss the finite volume effects in the Wigner formula connecting time delays to phase shifts. The results reported involve two- and four-qubit calculations, and we discuss the possibility of larger scale computations in the near future.}, issn = {2470-0010}, doi = {10.1103/PhysRevD.104.054507}, author = {Gustafson, Erik and Zhu, Yingyue and Dreher, Patrick and Linke, Norbert M. and Meurice, Yannick} } @article { WOS:000694043500003, title = {Reentrant Bloch ferromagnetism}, journal = {Phys. Rev. B}, volume = {104}, number = {10}, year = {2021}, month = {SEP 8}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {An interacting electron liquid in two (2D) and three (3D) dimensions may undergo a paramagnetic-to-ferromagnetic quantum spin polarization transition at zero applied magnetic field, driven entirely by exchange interactions, as the system density (n) is decreased. This is known as Bloch ferromagnetism. We show theoretically that the application of an external magnetic field (B), which directly spin polarizes the system through Zeeman spin splitting, has an interesting effect on Bloch ferromagnetism if the applied field and carrier density are both decreased (from some initial applied high magnetic field at a high carrier density) in a power-law manner, B similar to n(p). For pp(c), the system may undergo two transitions if starting from the fully spin-polarized state: first, a weak second-order transition at high density and field from the field-induced fully polarized phase to the partially polarized phase; and then, at a lower field and density, a reentrant first-order transition back to the fully spin-polarized phase again with a single Fermi surface.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.104.L100405}, author = {DinhDuy Vu and Das Sarma, S.} } @article { WOS:000687394800001, title = {Relativistic aspects of orbital and magnetic anisotropies in the chemical bonding and structure of lanthanide molecules}, journal = {New J. Phys.}, volume = {23}, number = {8}, year = {2021}, month = {AUG}, publisher = {IOP PUBLISHING LTD}, type = {Article}, abstract = {The electronic structure of magnetic lanthanide atoms is fascinating from a fundamental perspective. They have electrons in a submerged open 4f shell lying beneath a filled 6s shell with strong relativistic correlations leading to a large magnetic moment and large electronic orbital angular momentum. This large angular momentum leads to strong anisotropies, i. e. orientation dependencies, in their mutual interactions. The long-ranged molecular anisotropies are crucial for proposals to use ultracold lanthanide atoms in spin-based quantum computers, the realization of exotic states in correlated matter, and the simulation of orbitronics found in magnetic technologies. Short-ranged interactions and bond formation among these atomic species have thus far not been well characterized. Efficient relativistic computations are required. Here, for the first time we theoretically determine the electronic and ro-vibrational states of heavy homonuclear lanthanide Er-2 and Tm-2 molecules by applying state-of-the-art relativistic methods. In spite of the complexity of their internal structure, we were able to obtain reliable spin-orbit and correlation-induced splittings between the 91 Er-2 and 36 Tm-2 electronic potentials dissociating to two ground-state atoms. A tensor analysis allows us to expand the potentials between the atoms in terms of a sum of seven spin-spin tensor operators simplifying future research. The strengths of the tensor operators as functions of atom separation are presented and relationships among the strengths, derived from the dispersive long-range interactions, are explained. Finally, low-lying spectroscopically relevant ro-vibrational energy levels are computed with coupled-channels calculations and analyzed.}, keywords = {lanthanide molecules, relativistic electronic structure, spin tensor decomposition, ultracold lanthanide atoms}, issn = {1367-2630}, doi = {10.1088/1367-2630/ac1a9a}, author = {Tiesinga, Eite and Klos, Jacek and Li, Ming and Petrov, Alexander and Kotochigova, Svetlana} } @article { WOS:000664440600010, title = {Reply to "Comment on {\textquoteright}Nonequilibrium steady state phases of the interacting Aubry-Andre-Harper model{\textquoteright}"}, journal = {Phys. Rev. B}, volume = {103}, number = {23}, year = {2021}, month = {JUN 21}, publisher = {AMER PHYSICAL SOC}, type = {Editorial Material}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.237102}, author = {Yoo, Yongchan and Lee, Junhyun and Swingle, Brian} } @article {poniatowski_resistivity_2021, title = {Resistivity saturation in an electron-doped cuprate}, journal = {Phys. Rev. B}, volume = {103}, number = {2}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {jan}, abstract = {We report the observation of resistivity saturation in lightly doped (x = 0.08) as-grown samples of the electron-doped cuprate La2-xCexCuO4. The saturation occurs at resistivity values roughly consistent with the phenomenological Mott-Ioffe-Regel criterion once the low effective carrier density of these materials is included in the analysis. These results imply that, at least for light doping, the high-temperature metallic phase of these materials is not necessarily strange and may be understood as simply a low-density metal.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.L020501}, author = {Poniatowski, Nicholas R. and Sarkar, Tarapada and Das Sarma, Sankar and Greene, Richard L.} } @article { WOS:000677582200001, title = {Resource-Optimized Fermionic Local-Hamiltonian Simulation on a Quantum Computer for Quantum Chemistry}, journal = {Quantum}, volume = {5}, year = {2021}, month = {JUL 26}, pages = {1-36}, publisher = {VEREIN FORDERUNG OPEN ACCESS PUBLIZIERENS QUANTENWISSENSCHAF}, type = {Article}, abstract = {The ability to simulate a fermionic system on a quantum computer is expected to revolutionize chemical engineering, materials design, nuclear physics, to name a few. Thus, optimizing the simulation circuits is of significance in harnessing the power of quantum computers. Here, we address this problem in two aspects. In the fault-tolerant regime, we optimize the R-z and T gate counts along with the ancilla qubit counts required, assuming the use of a product-formula algorithm for implementation. We obtain a savings ratio of two in the gate counts and a savings ratio of eleven in the number of ancilla qubits required over the state of the art. In the pre-fault tolerant regime, we optimize the two-qubit gate counts, assuming the use of the variational quantum eigensolver (VQE) approach. Specific to the latter, we present a framework that enables bootstrapping the VQE progression towards the convergence of the ground-state energy of the fermionic system. This framework, based on perturbation theory, is capable of improving the energy estimate at each cycle of the VQE progression, by about a factor of three closer to the known ground-state energy compared to the standard VQE approach in the test-bed, classically-accessible system of the water molecule. The improved energy estimate in turn results in a commensurate level of savings of quantum resources, such as the number of qubits and quantum gates, required to be within a pre-specified tolerance from the known ground-state energy. We also explore a suite of generalized transformations of fermion to qubit operators and show that resource-requirement savings of up to more than 20\%, in small instances, is possible.}, issn = {2521-327X}, author = {Wang, Qingfeng and Li, Ming and Monroe, Christopher and Nam, Yunseong} } @article {osborn_reversible_2021, title = {Reversible {Fluxon} {Logic} {With} {Optimized} {CNOT} {Gate} {Components}}, journal = {IEEE Trans. Appl. Supercond.}, volume = {31}, number = {2}, year = {2021}, note = {Place: 445 HOES LANE, PISCATAWAY, NJ 08855-4141 USA Publisher: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC Type: Article}, month = {mar}, abstract = {

Reversible logic gates were previously implemented in superconducting circuits as adiabatic-reversible gates, which are powered with a sufficiently slow clock. In contrast, we are studying ballistic-reversible gates, where fluxons serve to both encode the information and power the gates. No power is applied to the gate apart from the energy of the input fluxons, and the two possible flux polarities represent the bit states. Undamped long Josephson junctions (LJJs), where fluxons move at practically constant speed from inertia, form the input and output channels of the gates. LJJs are connected in the gates by circuit interfaces, which are designed to allow the ballistic scattering from input to output fluxon states, using the temporary excitation of a localized mode. The duration of the resonant scattering determines the operation time of the gate, approximately a few Josephson plasma periods. Due to the coherent conversions between fluxon and localized modes, the ballistic gates can be very efficient: In our simulations, only a few percent of the fluxon{\textquoteright}s energy are dissipated in the gate operation. Ballistic-reversible gates can be combined with other nonballistic gate circuits to extend the range of gate functionalities. Here, we describe how the CNOT can be built as a structure that includes the Identity-else-Same-gives-NOT (IDSN) and store-and-launch (SNL) gates. The IDSN is a 2-b ballistic gate, which we describe and analyze in terms of equivalent 1-b circuits. The SNL is a clocking gate, which allows the storage of a bit and the clocked launch of a fluxon on a bit-state-dependent output path. In the CNOT, the SNL gates provide the necessary routing and fluxon synchronization for the input to the IDSN gate.

}, keywords = {Ballistic signaling, fluxons, power efficient, reversible computing, superconducting logic circuits}, issn = {1051-8223}, doi = {10.1109/TASC.2020.3035344}, author = {Osborn, Kevin D. and Wustmann, Waltraut} } @conference { WOS:000722581700055, title = {RF Signal Classification using Boolean Reservoir Computing on an FPGA}, booktitle = {2021 INTERNATIONAL JOINT CONFERENCE ON NEURAL NETWORKS (IJCNN)}, series = {IEEE International Joint Conference on Neural Networks (IJCNN)}, year = {2021}, note = {International Joint Conference on Neural Networks (IJCNN), ELECTR NETWORK, JUL 18-22, 2021}, publisher = {Int Neural Network Soc; IEEE Computat Intelligence Soc}, organization = {Int Neural Network Soc; IEEE Computat Intelligence Soc}, type = {Proceedings Paper}, abstract = {Networks of Boolean logic gates exhibiting complex dynamical behavior are promising reservoirs for hardware-accelerated reservoir computing. Using an FPGA, we explore the parameter space of both clocked and unclocked Boolean networks, and identify configurations that are suitable for information processing. We use an FPGA-based reservoir to process a subset of the DeepSig 2016 dataset, showing classification accuracy using logistic regression competitive with a state-of-the-art convolutional neural network, achieved with a fraction of the trainable parameters.}, keywords = {Boolean networks, FPGA, hardware acceleration, reservoir computing, RF classification}, isbn = {978-0-7381-3366-9}, issn = {2161-4393}, doi = {10.1109/IJCNN52387.2021.9533342}, author = {Komkov, Heidi and Pocher, Liam and Restelli, Alessandro and Hunt, Brian and Lathrop, Daniel} } @article { WOS:000658822200035, title = {Roaming pathways and survival probability in real-time collisional dynamics of cold and controlled bialkali molecules}, journal = {Sci Rep}, volume = {11}, number = {1}, year = {2021}, month = {MAY 19}, publisher = {NATURE RESEARCH}, type = {Article}, abstract = {Perfectly controlled molecules are at the forefront of the quest to explore chemical reactivity at ultra low temperatures. Here, we investigate for the first time the formation of the long-lived intermediates in the time-dependent scattering of cold bialkali 23Na87Rb molecules with and without the presence of infrared trapping light. During the nearly 50 nanoseconds mean collision time of the intermediate complex, we observe unconventional roaming when for a few tens of picoseconds either NaRb or Na2 and Rb2 molecules with large relative separation are formed before returning to the four-atom complex. We also determine the likelihood of molecular loss when the trapping laser is present during the collision. We find that at a wavelength of 1064 nm the Na2Rb2 complex is quickly destroyed and thus that the 23Na87Rb molecules are rapidly lost.}, issn = {2045-2322}, doi = {10.1038/s41598-021-90004-0}, author = {Klos, Jacek and Guan, Qingze and Li, Hui and Li, Ming and Tiesinga, Eite and Kotochigova, Svetlana} } @article { WOS:000647126400002, title = {Screening, Friedel oscillations, RKKY interaction, and Drude transport in anisotropic two-dimensional systems}, journal = {Phys. Rev. B}, volume = {103}, number = {16}, year = {2021}, month = {APR 7}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We investigate the effect of the mass anisotropy on Friedel oscillations, Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, screening properties, and Boltzmann transport in two-dimensional (2D) metallic and doped semiconductor systems. We calculate the static polarizability and the dielectric function within the random phase approximation with the mass anisotropy fully taken into account without making any effective isotropic approximation in the theory. We find that carrier screening exhibits an isotropic behavior for small momenta despite the anisotropy of the system and becomes strongly anisotropic above a certain threshold momentum. Such an anisotropy of screening leads to anisotropic Friedel oscillations, and an anisotropic RKKY interaction characterized by a periodicity dependent on the direction between the localized magnetic moments. We also explore the disorder limited dc transport properties in the presence of mass anisotropy based on the Boltzmann transport theory. Interestingly, we find that the anisotropy ratio of the short-range disorder limited resistivity along the heavy- and light-mass directions is always the same as the mass anisotropy ratio, whereas for the long-range disorder limited resistivity the anisotropy ratio is the same as the mass ratio only in the low-density limit and saturates to the square root of the mass ratio in the high-density limit. Our theoretical work should apply to many existing and to-be-discovered anisotropic 2D systems.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.165303}, author = {Ahn, Seongjin and Das Sarma, S.} } @article { WOS:000714581000004, title = {Self-Bayesian aberration removal via constraints for ultracold atom microscopy}, journal = {Phys. Rev. Res.}, volume = {3}, number = {4}, year = {2021}, month = {OCT 29}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {High-resolution imaging of ultracold atoms typically requires custom high numerical aperture (NA) optics, as is the case for quantum gas microscopy. These high NA objectives involve many optical elements, each of which contributes to loss and light scattering, making them unsuitable for quantum backaction limited {\textquoteleft}{\textquoteleft}weak{{\textquoteright}{\textquoteright}} measurements. We employ a low-cost high NA aspheric lens as an objective for a practical and economical-although aberrated-high-resolution microscope to image Rb-87 Bose-Einstein condensates. Here, we present a methodology for digitally eliminating the resulting aberrations that is applicable to a wide range of imaging strategies and requires no additional hardware. We recover nearly the full NA of our objective, thereby demonstrating a simple and powerful digital aberration correction method for achieving optimal microscopy of quantum objects. This reconstruction relies on a high-quality measure of our imaging system{\textquoteright}s even-order aberrations from density-density correlations measured with differing degrees of defocus. We demonstrate our aberration compensation technique using phase-contrast imaging, a dispersive imaging technique directly applicable to quantum backaction limited measurements. Furthermore, we show that our digital correction technique reduces the contribution of photon shot noise to density-density correlation measurements which would otherwise contaminate the desired quantum projection noise signal in weak measurements.}, doi = {10.1103/PhysRevResearch.3.043087}, author = {Altuntas, Emine and Spielman, I. B.} } @article { WOS:000704295900053, title = {Single-Molecule Measurements Spatially Probe States Involved in Electron Transfer from CdSe/CdS Core/Shell Nanorods}, journal = {J. Phys. Chem. C}, volume = {125}, number = {38, SI}, year = {2021}, month = {SEP 30}, pages = {21246-21253}, publisher = {AMER CHEMICAL SOC}, type = {Article}, abstract = {Semiconductor nanorods with charge-accepting molecules adsorbed on their surfaces serve as model systems for solar energy conversion. An electron photoexcited from the valence band of the nanorod to a high-energy state in the conduction band will relax and transfer to a state in the molecule, producing a long-lived charge-separated state that facilitates charge extraction and thereby enables photochemical reactions. Characterizing the dynamics of the charge-separation process and the electronic states involved is essential for a microscopic understanding of photocatalysis involving these materials, but this information is obscured in ensemble measurements due to the random placement of molecules on the nanorod surfaces. Here, we show that measurements on individual CdSe/CdS core/shell nanorods functionalized by single methyl viologen molecules provide information about the distribution of electron-transfer rates from confined states in the nanorods to states in the molecules. By comparing this transfer-rate distribution to the predictions of a tight-binding model, we find that charge transfer most likely involves hot electrons in an excited conduction-band state, rather than electrons that have fully thermalized to the conduction-band edge. The ability to extract hot electrons from semiconductor nanocrystals may help enable energy-efficient photocatalysis, and the single-particle charge-transfer method may serve as a widely applicable tool to probe the spatial distribution of electronic states in nanocrystals.}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.1c06581}, author = {Morin, Rachel M. and Bryant, Garnett W. and Shevchenko, V, Elena and Sha, Yuchen and Pelton, Matthew} } @article { WOS:000672632500003, title = {Single-Shot Readout of a Solid-State Spin in a Decoherence-Free Subspace}, journal = {Phys. Rev. Appl.}, volume = {15}, number = {3}, year = {2021}, month = {MAR 26}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The efficient single-photon-emission capabilities of quantum dot molecules position them as promising platforms for quantum information processing. Furthermore, quantum dot molecules feature a {\textquoteleft}{\textquoteleft}decoherence-free{{\textquoteright}{\textquoteright}} subspace that enables spin qubits with long coherence times. To efficiently read out the spin state within this subspace requires the optical cycling of isolated transitions that originate from a triplet manifold within the quantum dot molecule. We propose and theoretically study a two-stage spinreadout protocol within this decoherence-free subspace that allows single-shot readout performance. The process incorporates a microwave pi pulse and optical cycling of the isolated transitions, which induces fluorescence that allows us to identify the initial spin state. This protocol offers enhanced readout fidelity compared to previous schemes that rely on the excitation of transitions that strongly decay to multiple ground states or require long initialization via slow optically forbidden transitions. By simulating the performance of the protocol, we show that an optimal spin-readout fidelity of over 97\% and single-shot readout performance are achievable for a photon-collection efficiency of just 0.12\%. This high readout performance for such realistic photon-collection conditions within the decoherence-free subspace expands the potential of quantum dot molecules as building blocks for quantum networks.}, issn = {2331-7019}, doi = {10.1103/PhysRevApplied.15.L031002}, author = {Farfurnik, D. and Pettit, R. M. and Luo, Z. and Waks, E.} } @article { WOS:000707419200012, title = {Singularities in nearly uniform one-dimensional condensates due to quantum diffusion}, journal = {Phys. Rev. A}, volume = {104}, number = {4}, year = {2021}, month = {OCT 14}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Dissipative systems often exhibit wavelength-dependent loss rates. One prominent example is Rydberg polaritons formed by electromagnetically induced transparency, which have long been a leading candidate for studying the physics of interacting photons and also hold promise as a platform for quantum information. In this system, dissipation is in the form of quantum diffusion, i.e., proportional to k(2) (k being the wavevector) and vanishing at long wavelengths as k -> 0. Here, we show that one-dimensional condensates subject to this type of loss are unstable to long-wavelength density fluctuations in an unusual manner: after a prolonged period in which the condensate appears to relax to a uniform state, local depleted regions quickly form and spread ballistically throughout the system. We connect this behavior to the leading-order equation for the nearly uniform condensate-a dispersive analog to the Kardar-Parisi-Zhang equation-which develops singularities in finite time. Furthermore, we show that the wavefronts of the depleted regions are described by purely dissipative solitons within a pair of hydrodynamic equations, with no counterpart in lossless condensates. We close by discussing conditions under which such singularities and the resulting solitons can be physically realized.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.104.L041303}, author = {Baldwin, C. L. and Bienias, P. and Gorshkov, V, A. and Gullans, M. J. and Maghrebi, M.} } @article { WOS:000672657300001, title = {Solitons in lattice field theories via tight-binding supersymmetry}, journal = {J. High Energy Phys.}, number = {7}, year = {2021}, month = {JUL 9}, publisher = {SPRINGER}, type = {Article}, abstract = {Reflectionless potentials play an important role in constructing exact solutions to classical dynamical systems (such as the Korteweg-de Vries equation), non-perturbative solutions of various large-N field theories (such as the Gross-Neveu model), and closely related solitonic solutions to the Bogoliubov-de Gennes equations in the theory of superconductivity. These solutions rely on the inverse scattering method, which reduces these seemingly unrelated problems to identifying reflectionless potentials of an auxiliary one-dimensional quantum scattering problem. There are several ways of constructing these potentials, one of which is quantum mechanical supersymmetry (SUSY). In this paper, motivated by recent experimental platforms, we generalize this framework to develop a theory of lattice solitons. We first briefly review the classical inverse scattering method in the continuum limit, focusing on the Korteweg-de Vries (KdV) equation and SU(N) Gross-Neveu model in the large N limit. We then generalize this methodology to lattice versions of interacting field theories. Our analysis hinges on the use of trace identities, which are relations connecting the potential of an equation of motion to the scattering data. For a discrete Schrodinger operator, such trace identities had been known as far back as Toda; however, we derive a new set of identities for the discrete Dirac operator. We then use these identities in a lattice Gross-Neveu and chiral Gross-Neveu (Nambu-Jona-Lasinio) model to show that lattice solitons correspond to reflectionless potentials associated with the discrete scattering problem. These models are of significance as they are equivalent to a mean-field theory of a lattice superconductor. To explicitly construct these solitons, we generalize supersymmetric quantum mechanics to tight-binding models. We show that a matrix transformation exists that maps a tight-binding model to an isospectral one which shares the same structure and scattering properties. The corresponding soliton solutions have both modulated hopping and onsite potential, the former of which has no analogue in the continuum limit. We explicitly compute both topological and non-topological soliton solutions as well as bound state spectra in the aforementioned models.}, keywords = {Lattice Integrable Models, Lattice Quantum Field Theory, Solitons Monopoles and Instantons}, issn = {1029-8479}, doi = {10.1007/JHEP07(2021)055}, author = {Balasubramanian, Shankar and Patoary, Abu and Galitski, Victor} } @article { WOS:000736648600001, title = {Spin-Valley Qubit Dynamics in Exchange-Coupled Silicon Quantum Dots}, journal = {PRX Quantum}, volume = {2}, number = {4}, year = {2021}, month = {DEC 23}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The presence of valley states is a significant obstacle to realizing quantum information technologies in silicon quantum dots, as leakage into alternate valley states can introduce errors into the computation. We use a perturbative analytical approach to study the dynamics of exchange-coupled quantum dots with valley degrees of freedom. We show that if the valley splitting is large and electrons are not properly initialized to valley eigenstates, then the time evolution of the system will lead to spin-valley entanglement. Spin-valley entanglement will also occur if the valley splitting is small and electrons are not initialized to the same valley state. Additionally, we show that for small valley splitting, spin-valley entanglement does not affect the measurement probabilities of two-qubit systems; however, systems with more qubits will be affected. This means that two-qubit gate fidelities measured in two-qubit systems may miss the effects of valley degrees of freedom. Our work shows how the existence of valleys may adversely affect multiqubit fidelities even when the system temperature is very low. Although this is not an immediate problem in Si qubits, because the current focus is on controlling individual qubits, our work points to a possible future issue in many-qubit Si circuits.}, doi = {10.1103/PRXQuantum.2.040358}, author = {Buterakos, Donovan and Das Sarma, Sankar} } @article { WOS:000645519800001, title = {Spontaneous pulse formation in edgeless photonic crystal resonators}, journal = {Nat. Photonics}, volume = {15}, number = {6}, year = {2021}, month = {JUN}, pages = {461+}, publisher = {NATURE RESEARCH}, type = {Article}, abstract = {Nonlinearity in complex systems leads to pattern formation through fundamental interactions between components. With integrated photonics, precision control of nonlinearity explores novel patterns and propels applications. In particular, Kerr-nonlinear resonators support stationary states-including Turing patterns-composed of a few interfering waves, and localized solitons composed of waves across a broad spectrum. Although Turing patterns emerge from an unstable Kerr resonator with sufficiently intense excitation, Kerr solitons do not form spontaneously under constant excitation, making this useful state challenging to access. Here we explore an edgeless photonic crystal resonator (PhCR) that enables spontaneous soliton formation in place of Turing patterns. We design the PhCR nanopattern for single-azimuthal-mode engineering of a group-velocity-dispersion defect that balances Kerr-nonlinear frequency shifts in favour of the soliton state. Our experiments establish PhCR solitons as modelocked pulses through ultraprecise optical-frequency measurements. We show that nanophotonics expand the palette for nonlinear engineering, enabling new phenomena and light sources. Researchers have demonstrated spontaneous soliton formation in an edgeless photonic crystal resonator.}, issn = {1749-4885}, doi = {10.1038/s41566-021-00800-3}, author = {Yu, Su-Peng and Cole, Daniel C. and Jung, Hojoong and Moille, Gregory T. and Srinivasan, Kartik and Papp, Scott B.} } @article { WOS:000647175700003, title = {Studying many-body localization in exchange-coupled electron spin qubits using spin-spin correlations}, journal = {Phys. Rev. B}, volume = {103}, number = {16}, year = {2021}, month = {APR 29}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We show that many-body localization (MBL) effects can be observed in a finite chain of exchange-coupled spin qubits in the presence of both exchange and magnetic noise, a system that has been experimentally realized in semiconductors and is a potential solid-state quantum computing platform. In addition to established measures of MBL, the level spacing ratio and the entanglement entropy, we propose another quantity, the spin-spin correlation function, that can be measured experimentally and is particularly well-suited to experiments in semiconductor-based electron spin qubit systems. We show that, in cases that the established measures detect as delocalized {\textquoteleft}{\textquoteleft}phases,{{\textquoteright}{\textquoteright}} the spin-spin correlation functions retain no memory of the system{\textquoteright}s initial state (i.e., the long-time value deviates significantly from the initial value), but that they do retain memory in cases that the established measures detect as localized {\textquoteleft}{\textquoteleft}phases.{{\textquoteright}{\textquoteright}} We also discover an interesting counterintuitive result that there is no clear tendency towards localization with increasing charge noise in small systems (3-10 spins). The proposed experiments should be feasible in the existing semiconductor spin qubit systems.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.165431}, author = {Throckmorton, Robert E. and Das Sarma, S.} } @article {shivam_studying_2021, title = {Studying {Viral} {Populations} with {Tools} from {Quantum} {Spin} {Chains}}, journal = {J. Stat. Phys.}, volume = {182}, number = {2}, year = {2021}, note = {Place: ONE NEW YORK PLAZA, SUITE 4600, NEW YORK, NY, UNITED STATES Publisher: SPRINGER Type: Article}, month = {feb}, abstract = {We study Eigen{\textquoteright}s model of quasi-species (Eigen in Selforganization of matter and the evolution of biological macromolecules. Naturwissenschaften 58(10):465, 1971), characterized by sequences that replicate with a specified fitness and mutate independently at single sites. The evolution of the population vector in time is then closely related to that of quantum spins in imaginary time. We employ multiple perspectives and tools from interacting quantum systems to examine growth and collapse of realistic viral populations, specifically considering excessive mutations in certain HIV proteins. All approaches used, including the simplest perturbation theory, give consistent results.

}, keywords = {Biological evolution, HIV, Quantum spin chains}, issn = {0022-4715}, doi = {10.1007/s10955-021-02716-2}, author = {Shivam, Saumya and Baldwin, Christopher L. and Barton, John and Kardar, Mehran and Sondhi, S. L.} } @article { WOS:000707469900008, title = {Superconductors with anomalous Floquet higher-order topology}, journal = {Phys. Rev. B}, volume = {104}, number = {14}, year = {2021}, month = {OCT 11}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We develop a general theory for two-dimensional (2D) anomalous Floquet higher-order topological superconductors (AFHOTSCs), which are dynamical Majorana-carrying phases of matter with no static counterpart. Despite the triviality of its bulk Floquet bands, an AFHOTSC generically features the simultaneous presence of corner-localized Majorana modes at both zero and pi/T quasienergies, a phenomenon beyond the scope of any static topological band theory. We show that the key to AFHOTSCs is their unavoidable singular behavior in the phase spectrum of the bulk time-evolution operator. By mapping such evolution-phase singularities to the stroboscopic boundary signatures, we classify 2D AFHOTSCs that are protected by a rotation group symmetry in symmetry class D. We further extract a higher-order topological index for unambiguously predicting the presence of Floquet corner Majorana modes, which we confirm numerically. Our theory serves as a milestone towards a dynamical topological theory for Floquet superconducting systems.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.104.L140502}, author = {Vu, DinhDuy and Zhang, Rui-Xing and Yang, Zhi-Cheng and Das Sarma, S.} } @article { WOS:000704414100002, title = {Symmetry-breaking signatures of multiple Majorana zero modes in one-dimensional spin-triplet superconductors}, journal = {Phys. Rev. B}, volume = {104}, number = {10}, year = {2021}, month = {SEP 28}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study the effects of various symmetry-breaking perturbations on the experimentally measurable signatures (such as conductance and Josephson response) of quasi-one-dimensional (quasi-1D) spin-triplet superconductors. In the first part of the paper, we numerically compute the zero and nonzero temperature conductances of the quasi-1D nanowires that host multiple Majorana zero modes. Following the discussion of the case of s-wave Rashba nanowires, we shift to the main focus, i.e., multi-channel spin-triplet superconductors. Applying gate voltages (which changes the symmetry of the spin-orbit coupling) as well as magnetic fields to the nanowire, tunes the system between different symmetry classes by splitting the multiple Majorana zero modes. We study how the conductance tracks the topological invariants and the spectra in all these cases. In the second part of the paper, we study the effects of the symmetry-induced spectrum-breaking on the Andreev spectra of Josephson junctions Similar to the case of the conductance studies, we find that the spectrum shows multiple zero-energy Andreev bound states in the highly symmetric case with mirror and chiral symmetries.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.104.104513}, author = {Ray, Arnab Barman and Sau, Jay D. and Mandal, Ipsita} } @article {liu_synthesis_2021, title = {Synthesis of {Narrow} {SnTe} {Nanowires} {Using} {Alloy} {Nanoparticles}}, journal = {ACS Appl. Electron. Mater.}, volume = {3}, number = {1}, year = {2021}, note = {Place: 1155 16TH ST, NW, WASHINGTON, DC 20036 USA Publisher: AMER CHEMICAL SOC Type: Article}, month = {jan}, pages = {184{\textendash}191}, abstract = {Topological crystalline insulator tin telluride (SnTe) provides a rich playground to examine interactions of correlated electronic states, such as ferroelectricity, topological surface states, and superconductivity. The study of SnTe nanowires may lead to even richer physics owing to the one-dimensional (1D) confinement effect and an increased contribution from the topological surface states. Thus, for transport measurements, SnTe nanowires must be synthesized with reduced diameters and high crystalline quality to ensure 1D confinement and phase coherence of the topological surface electrons. This study reports a facile growth method to produce narrow SnTe nanowires with a high yield using alloy nanoparticles as growth catalysts. The average diameter of the SnTe nanowires grown using alloy nanoparticles is 85 nm, nearly a factor of three reduction compared to the average diameter of 240 nm when using gold nanoparticles as growth catalysts. Transport measurements reveal the effect of the nanowire diameter on the residual resistance ratio and magnetoresistance. Particularly, the ferroelectric transition temperature for SnTe evolves systematically with the nanowire diameter. In situ cryogenic cooling of narrow SnTe nanowires in a transmission electron microscope directly reveals the cubic to rhombohedral structural transition, which is associated with the ferroelectric transition. Thus, these narrow SnTe nanowires represent a model system to study electronic states arising from 1D confinement, such as 1D topological superconductivity and potential multiband superconductivity.

}, keywords = {ferroelectric transition, Nanowires, tin telluride, topological crystalline insulators, vapor-liquid-solid growth}, doi = {10.1021/acsaelm.0c00740}, author = {Liu, Pengzi and Han, Hyeuk Jin and Wei, Julia and Hynek, David and Hart, James L. and Han, Myung Geun and Trimble, Christie Jordan and Williams, James and Zhu, Yimei and Cha, Judy J.} } @article { WOS:000724242500007, title = {Tailoring broadband Kerr soliton microcombs via post-fabrication tuning of the geometric dispersion}, journal = {Appl. Phys. Lett.}, volume = {119}, number = {12}, year = {2021}, month = {SEP 20}, publisher = {AIP Publishing}, type = {Article}, abstract = {Geometric dispersion in integrated microresonators plays a major role in nonlinear optics applications, especially at short wavelengths, to compensate the natural material normal dispersion. Tailoring of geometric confinement allows for anomalous dispersion, which, in particular, enables the formation of microcombs that can be tuned into the dissipative Kerr soliton (DKS) regime. Due to processes like soliton-induced dispersive wave generation, broadband DKS combs are particularly sensitive to higher-order dispersion, which, in turn, is sensitive to the ring dimensions at the nanometer-level. For microrings exhibiting a rectangular cross section, the ring width and thickness are the two main control parameters to achieve the targeted dispersion. The former can be easily varied through parameter variation within the lithography mask, yet the latter is defined by the film thickness during growth of the starting material stack and can show a significant variation (few percent of the total thickness) over a single wafer. In this Letter, we demonstrate that controlled dry-etching allows for fine tuning of the device layer (silicon nitride) thickness at the wafer level, allowing multi-project wafers targeting different wavelength bands and post-fabrication trimming in air-clad ring devices. We demonstrate that such dry etching does not significantly affect either the silicon nitride surface roughness or the optical quality of the devices, thereby enabling fine tuning of the dispersion and the spectral shape of the resulting DKS states. (C) 2021 Author(s).}, issn = {0003-6951}, doi = {10.1063/5.0061238}, author = {Moille, Gregory and Westly, Daron and Orji, Ndubuisi George and Srinivasan, Kartik} } @article { WOS:000646317500004, title = {Temperature-dependent energy diffusion in chaotic spin chains}, journal = {Phys. Rev. B}, volume = {103}, number = {11}, year = {2021}, month = {MAR 25}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study the temperature dependence of energy diffusion in two chaotic gapped quantum spin chains, a tilted-field Ising model and an XZ model, using an open-system approach. We introduce an energy imbalance by coupling the chain to thermal baths at its boundary and study the nonequilibrium steady states of the resulting Lindblad dynamics using a matrix product operator ansatz for the density matrix. We define an effective local temperature profile by comparing local reduced density matrices in the steady state with those of a uniform thermal state. We then measure the energy current for a variety of driving temperatures and extract the temperature dependence of the energy diffusion constant. For the Ising model, we are able to study temperatures well below the energy gap and find a regime of dilute excitations where rare three-body collisions control energy diffusion. A kinetic model correctly predicts the observed exponential increase of the energy diffusion constant at low temperatures. For the XZ model, we are only able to access intermediate to high temperatures relative to the energy gap, and we show that the data are well described by an expansion around the infinite temperature limit. We also discuss the limitations of the particular driving scheme and suggest that lower temperatures can be accessed using larger baths.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.115148}, author = {Zanoci, Cristian and Swingle, Brian} } @article { WOS:000680137400005, title = {Temporal shaping of single photons by engineering exciton dynamics in a single quantum dot}, journal = {APL Phontonics}, volume = {6}, number = {8}, year = {2021}, month = {AUG 1}, publisher = {AMER INST PHYSICS}, type = {Article}, abstract = {The majority of photonic quantum information technologies rely on single photons that have high purity and indistinguishability. Although solid-state quantum emitters can serve such single photons on demand, their asymmetric temporal and spatial mode profiles limit the optimal efficiency and fidelity of quantum interaction. Here, we demonstrate single-photon pulses at a telecom wavelength with a Gaussian-like temporal mode profile from a cavity-coupled single quantum dot. Engineering the exciton dynamics via multi-exciton cascade recombination and cavity detuning enables us to modify the rise and decay dynamics of single excitons. Furthermore, the cascade recombination process temporally retards the single-exciton emission from the background emission, leading to possible purification of single photons at high excitation power. In addition, coupling quantum dots into a low Q cavity mode leads to a Gaussian-like spatial mode profile, which brings a high collection efficiency. This approach paves the way for producing single photons with an optimized temporal and spatial waveform.}, issn = {2378-0967}, doi = {10.1063/5.0045241}, author = {Kim, Kyu-Young and Richardson, Christopher J. K. and Waks, Edo and Kim, Je-Hyung} } @article {ahn_theory_2021, title = {Theory of anisotropic plasmons}, journal = {Phys. Rev. B}, volume = {103}, number = {4}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {jan}, abstract = {We develop the complete theory for the collective plasmon modes of an interacting electron system in the presence of explicit mass (or velocity) anisotropy in the corresponding noninteracting situation, with the effective Fermi velocity being different along different axes. Such effective mass anisotropy is common in solid state materials (e.g., silicon or germanium), where the Fermi surface is often not spherical. We find that the plasmon dispersion itself develops significant anisotropy in such systems, and the commonly used isotropic approximation of using a density of states or optical effective mass does not work for the anisotropic system. We predict a qualitatively new phenomenon in anisotropic systems with no corresponding isotropic analog, where the plasmon mode along one direction decays into electron-hole pairs through Landau damping while the mode remains undamped and stable along a different direction.

}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.L041303}, author = {Ahn, Seongjin and Sankar Das Sarma} } @article { WOS:000681124600002, title = {Theory of Coulomb blockaded transport in realistic Majorana nanowires}, journal = {Phys. Rev. B}, volume = {104}, number = {8}, year = {2021}, month = {AUG 3}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Coulomb blockaded transport of topological superconducting nanowires provides an opportunity to probe the localization of states at both ends of the system in a two-terminal geometry. In addition, it provides a way for checking for subgap states away from the leads. At the same time, Coulomb blockade transport is difficult to analyze because of the interacting nature of the problem arising from the nonperturbative Coulomb interaction inherent in the phenomenon. Here we show that the Coulomb blockade transport can be modeled at the same level of complexity as quantum point contact tunneling that has routinely been used in mesoscopic physics to understand nanowire experiments provided we consider the regime where the tunneling rate is below the equilibration rate of the nanowire. This assumption leads us to a generalized Meir-Wingreen formula for the tunnel conductance which we use to study various features of the nanowire such as Andreev bound states, self-energy, and soft gap. We anticipate that our theory will provide a route to interpret Coulomb blockade transport in hybrid Majorana systems as resulting from features of the nanowire, such as Andreev bound states and soft gaps.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.104.085403}, author = {Lai, Yi-Hua and Das Sarma, Sankar and Sau, Jay D.} } @article {childs_theory_2021, title = {Theory of {Trotter} {Error} with {Commutator} {Scaling}}, journal = {Phys. Rev. X}, volume = {11}, number = {1}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {feb}, abstract = {The Lie-Trotter formula, together with its higher-order generalizations, provides a direct approach to decomposing the exponential of a sum of operators. Despite significant effort, the error scaling of such product formulas remains poorly understood. We develop a theory of Trotter error that overcomes the limitations of prior approaches based on truncating the Baker-Campbell-Hausdorff expansion. Our analysis directly exploits the commutativity of operator summands, producing tighter error bounds for both real- and imaginary-time evolutions. Whereas previous work achieves similar goals for systems with geometric locality or Lie-algebraic structure, our approach holds, in general. We give a host of improved algorithms for digital quantum simulation and quantum Monte Carlo methods, including simulations of second-quantized plane-wave electronic structure, k-local Hamiltonians, rapidly decaying power-law interactions, clustered Hamiltonians, the transverse field Ising model, and quantum ferromagnets, nearly matching or even outperforming the best previous results. We obtain further speedups using the fact that product formulas can preserve the locality of the simulated system. Specifically, we show that local observables can be simulated with complexity independent of the system size for power-law interacting systems, which implies a Lieb-Robinson bound as a by-product. Our analysis reproduces known tight bounds for first- and second-order formulas. Our higher-order bound overestimates the complexity of simulating a one-dimensional Heisenberg model with an even-odd ordering of terms by only a factor of 5, and it is close to tight for power-law interactions and other orderings of terms. This result suggests that our theory can accurately characterize Trotter error in terms of both asymptotic scaling and constant prefactor.

}, issn = {2160-3308}, doi = {10.1103/PhysRevX.11.011020}, author = {Childs, Andrew M. and Su, Yuan and Tran, Minh C. and Wiebe, Nathan and Zhu, Shuchen} } @article {pan_three-terminal_2021, title = {Three-terminal nonlocal conductance in {Majorana} nanowires: {Distinguishing} topological and trivial in realistic systems with disorder and inhomogeneous potential}, journal = {Phys. Rev. B}, volume = {103}, number = {1}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {jan}, abstract = {We develop a theory for the three-terminal nonlocal conductance in Majorana nanowires as existing in the superconductor-semiconductor hybrid structures in the presence of superconducting proximity, spin-orbit coupling, and Zeeman splitting. The key question addressed is whether such nonlocal conductance can decisively distinguish between trivial and topological Majorana scenarios in the presence of chemical potential inhomogeneity and random impurity disorder. We calculate the local electrical as well as nonlocal electrical and thermal conductance of the pristine nanowire (good zero-bias conductance peaks), the nanowire in the presence of quantum dots and inhomogeneous potential (bad zero-bias conductance peaks), and the nanowire in the presence of large disorder (ugly zero-bias conductance peaks). The local conductance by itself is incapable of distinguishing the trivial states from the topological states since zero-bias conductance peaks are generic in the presence of disorder and inhomogeneous potential. The nonlocal conductance, which in principle is capable of providing the bulk gap closing and reopening information at the topological quantum phase transition, is found to be far too weak in magnitude to be particularly useful in the presence of disorder and inhomogeneous potential. Therefore, we focus on the question of whether the combination of the local, nonlocal electrical, and thermal conductance can separate the good, bad, and ugly zero-bias conductance peaks in finite-length wires. Our paper aims to provide a guide to future experiments, and we conclude that a combination of all three measurements would be necessary for a decisive demonstration of topological Majorana zero modes in nanowires-positive signals corresponding to just one kind of measurements are likely to be false positives arising from disorder and inhomogeneous potential.

}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.014513}, author = {Pan, Haining and Sau, Jay D. and Sankar Das Sarma} } @article { WOS:000655930100005, title = {Topological Defect Engineering and PT Symmetry in Non-Hermitian Electrical Circuits}, journal = {Phys. Rev. Lett.}, volume = {126}, number = {21}, year = {2021}, month = {MAY 28}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We employ electric circuit networks to study topological states of matter in non-Hermitian systems enriched by parity-time symmetry PT and chiral symmetry anti-PT (APT). The topological structure manifests itself in the complex admittance bands which yields excellent measurability and signal to noise ratio. We analyze the impact of PT-symmetric gain and loss on localized edge and defect states in a non-Hermitian Su-Schrieffer-Heeger (SSH) circuit. We realize all three symmetry phases of the system, including the APT-symmetric regime that occurs at large gain and loss. We measure the admittance spectrum and eigenstates for arbitrary boundary conditions, which allows us to resolve not only topological edge states, but also a novel PT-symmetric Z(2) invariant of the bulk. We discover the distinct properties of topological edge states and defect states in the phase diagram. In the regime that is not PT symmetric, the topological defect state disappears and only reemerges when APT symmetry is reached, while the topological edge states always prevail and only experience a shift in eigenvalue. Our findings unveil a future route for topological defect engineering and tuning in non-Hermitian systems of arbitrary dimension.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.126.215302}, author = {Stegmaier, Alexander and Imhof, Stefan and Helbig, Tobias and Hoefmann, Tobias and Lee, Ching Hua and Kremer, Mark and Fritzsche, Alexander and Feichtner, Thorsten and Klembt, Sebastian and Hofling, Sven and Boettcher, Igor and Fulga, Ion Cosma and Ma, Libo and Schmidt, Oliver G. and Greiter, Martin and Kiessling, Tobias and Szameit, Alexander and Thomale, Ronny} } @article {19181, title = {Topological features without a lattice in Rashba spin-orbit coupled atoms}, journal = {Nature Communications}, volume = {12}, year = {2021}, month = {01/2021}, abstract = {Topological order can be found in a wide range of physical systems, from crystalline solids, photonic meta-materials and even atmospheric waves to optomechanic, acoustic and atomic systems. Topological systems are a robust foundation for creating quantized channels for transporting electrical current, light, and atmospheric disturbances. These topological effects are quantified in terms of integer-valued {\textquoteleft}invariants{\textquoteright}, such as the Chern number, applicable to the quantum Hall effect, or the\ Z2Z2\ invariant suitable for topological insulators. Here, we report the engineering of Rashba spin-orbit coupling for a cold atomic gas giving non-trivial topology, without the underlying crystalline structure that conventionally yields integer Chern numbers. We validated our procedure by spectroscopically measuring both branches of the Rashba dispersion relation which touch at a single Dirac point. We then measured the quantum geometry underlying the dispersion relation using matter-wave interferometry to implement a form of quantum state tomography, giving a Berry{\textquoteright}s phase with magnitude\ *Ï€*. This implies that opening a gap at the Dirac point would give two dispersions (bands) each with half-integer Chern number, potentially implying new forms of topological transport.

Recent advances in realizing optical frequency combs using nonlinear parametric processes in integrated photonic resonators have revolutionized on-chip optical clocks, spectroscopy and multichannel optical communications. At the same time, the introduction of topological physics in photonic systems has allowed the design of photonic devices with novel functionalities and inherent robustness against fabrication disorders. Here we use topological design principles to theoretically propose the generation of optical frequency combs and temporal dissipative Kerr solitons in a two-dimensional array of coupled ring resonators that creates a synthetic magnetic field for photons and exhibits topological edge states. We show that these topological edge states constitute a travelling-wave super-ring resonator that leads to the generation of coherent nested optical frequency combs, as well as the self-formation of nested temporal solitons and Turing rolls that are remarkably phase-locked over more than 40 rings. Moreover, we show that the topological nested solitons are robust against defects in the lattice, and a single nested soliton achieves a mode efficiency of over 50{\%}, an order of magnitude higher than single-ring frequency combs. Our topological frequency comb works in a parameter regime that can be readily accessed using existing low-loss integrated photonic platforms like silicon nitride.

}, isbn = {1745-2481}, doi = {10.1038/s41567-021-01302-3}, url = {https://doi.org/10.1038/s41567-021-01302-3}, author = {Mittal, Sunil and Moille, Gregory and Srinivasan, Kartik and Chembo, Yanne K. and Hafezi, Mohammad} } @article {21626, title = {Topological Order and Criticality in (2+1)D Monitored Random Quantum Circuits}, journal = {Phys. Rev. Lett.}, volume = {127}, year = {2021}, month = {Dec}, pages = {235701}, doi = {10.1103/PhysRevLett.127.235701}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.127.235701}, author = {Lavasani, Ali and Alavirad, Yahya and Barkeshli, Maissam} } @article { WOS:000646178000004, title = {Torus spectroscopy of the Gross-Neveu-Yukawa quantum field theory: Free Dirac versus chiral Ising fixed point}, journal = {Phys. Rev. B}, volume = {103}, number = {12}, year = {2021}, month = {MAR 12}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We establish the universal torus low-energy spectra at the free Dirac fixed point and at the strongly coupled chiral Ising fixed point and their subtle crossover behavior in the Gross-Neuveu-Yukawa field theory with n(D) = 4 component Dirac spinors in D = (2 + 1) dimensions. These fixed points and the field theories are directly relevant for the long-wavelength physics of certain interacting Dirac systems, such as repulsive spinless fermions on the honeycomb lattice or pi-flux square lattice. The torus energy spectrum has been shown previously to serve as a characteristic fingerprint of relativistic fixed points and is a powerful tool to discriminate quantum critical behavior in numerical simulations. Here, we use a combination of exact diagonalization and quantum Monte Carlo simulations of strongly interacting fermionic lattice models, to compute the critical torus energy spectrum on finite-size clusters with periodic boundaries and extrapolate them to the thermodynamic limit. Additionally, we compute the torus energy spectrum analytically using the perturbative expansion in epsilon = 4 - D, which is in good agreement with the numerical results, thereby validating the presence of the chiral Ising fixed point in the lattice models at hand. We show that the strong interaction between the spinor field and the scalar order-parameter field strongly influences the critical torus energy spectrum and we observe prominent multiplicity features related to an emergent symmetry predicted from the quantum field theory. Building on these results we are able to address the subtle crossover physics of the low-energy spectrum flowing from the chiral Ising fixed point to the Dirac fixed point, and analyze earlier flawed attempts to extract Fermi velocity renormalizations from the low-energy spectrum.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.125128}, author = {Schuler, Michael and Hesselmann, Stephan and Whitsitt, Seth and Lang, Thomas C. and Wessel, Stefan and Laeuchli, Andreas M.} } @article { WOS:000711950200004, title = {Toward simulating quantum field theories with controlled phonon-ion dynamics: A hybrid analog-digital approach}, journal = {Phys. Rev. Res.}, volume = {3}, number = {4}, year = {2021}, month = {OCT 26}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Quantum field theories are the cornerstones of modern physics, providing relativistic and quantum mechanical descriptions of physical systems at the most fundamental level. Simulating real-time dynamics within these theories remains elusive in classical computing. This provides a unique opportunity for quantum simulators, which hold the promise of revolutionizing our simulation capabilities. Trapped-ion systems are successful quantum-simulator platforms for quantum many-body physics and can operate in digital, or gate-based, and analog modes. Inspired by the progress in proposing and realizing quantum simulations of a number of relativistic quantum field theories using trapped-ion systems, and by the hybrid analog-digital proposals for simulating interacting boson-fermion models, we propose hybrid analog-digital quantum simulations of selected quantum field theories, taking recent developments to the next level. On one hand, the semi-digital nature of this proposal offers more flexibility in engineering generic model interactions compared with a fully-analog approach. On the other hand, encoding the bosonic fields onto the phonon degrees of freedom of the trapped-ion system allows a more efficient usage of simulator resources, and a more natural implementation of intrinsic quantum operations in such platforms. This opens up ways for simulating complex dynamics of, e.g., Abelian and non-Abelian gauge theories, by combining the benefits of digital and analog schemes.}, doi = {10.1103/PhysRevResearch.3.043072}, author = {Davoudi, Zohreh and Linke, Norbert M. and Pagano, Guido} } @article { WOS:000655094800001, title = {Towards integrated photonic interposers for processing octave-spanning microresonator frequency combs}, journal = {Light-Sci. Appl.}, volume = {10}, number = {1}, year = {2021}, month = {MAY 26}, publisher = {SPRINGERNATURE}, type = {Article}, abstract = {Microcombs-optical frequency combs generated in microresonators-have advanced tremendously in the past decade, and are advantageous for applications in frequency metrology, navigation, spectroscopy, telecommunications, and microwave photonics. Crucially, microcombs promise fully integrated miniaturized optical systems with unprecedented reductions in cost, size, weight, and power. However, the use of bulk free-space and fiber-optic components to process microcombs has restricted form factors to the table-top. Taking microcomb-based optical frequency synthesis around 1550 nm as our target application, here, we address this challenge by proposing an integrated photonics interposer architecture to replace discrete components by collecting, routing, and interfacing octave-wide microcomb-based optical signals between photonic chiplets and heterogeneously integrated devices. Experimentally, we confirm the requisite performance of the individual passive elements of the proposed interposer-octave-wide dichroics, multimode interferometers, and tunable ring filters, and implement the octave-spanning spectral filtering of a microcomb, central to the interposer, using silicon nitride photonics. Moreover, we show that the thick silicon nitride needed for bright dissipative Kerr soliton generation can be integrated with the comparatively thin silicon nitride interposer layer through octave-bandwidth adiabatic evanescent coupling, indicating a path towards future system-level consolidation. Finally, we numerically confirm the feasibility of operating the proposed interposer synthesizer as a fully assembled system. Our interposer architecture addresses the immediate need for on-chip microcomb processing to successfully miniaturize microcomb systems and can be readily adapted to other metrology-grade applications based on optical atomic clocks and high-precision navigation and spectroscopy.}, issn = {2047-7538}, doi = {10.1038/s41377-021-00549-y}, author = {Rao, Ashutosh and Moille, Gregory and Lu, Xiyuan and Westly, Daron A. and Sacchetto, Davide and Geiselmann, Michael and Zervas, Michael and Papp, Scott B. and Bowers, John and Srinivasan, Kartik} } @article { WOS:000681427700005, title = {Trapped Electrons and Ions as Particle Detectors}, journal = {Phys. Rev. Lett.}, volume = {127}, number = {6}, year = {2021}, month = {AUG 5}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Electrons and ions trapped with electromagnetic fields have long served as important high-precision metrological instruments, and more recently have also been proposed as a platform for quantum information processing. Here we point out that these systems can also be used as highly sensitive detectors of passing charged particles, due to the combination of their extreme charge-to-mass ratio and low-noise quantum readout and control. In particular, these systems can be used to detect energy depositions many orders of magnitude below typical ionization scales. As illustrations, we suggest some applications in particle physics. We outline a nondestructive time-of-flight measurement capable of sub-eV energy resolution for slowly moving, collimated particles. We also show that current devices can be used to provide competitive sensitivity to models where ambient dark matter particles carry small electric millicharges << e. Our calculations may also be useful in the characterization of noise in quantum computers coming from backgrounds of charged particles.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.127.061804}, author = {Carney, Daniel and Haffner, Hartmut and Moore, David C. and Taylor, Jacob M.} } @article {zhang_tunable_2021, title = {Tunable fragile topology in {Floquet} systems}, journal = {Phys. Rev. B}, volume = {103}, number = {12}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {mar}, abstract = {We extend the notion of fragile topology to periodically driven systems. We demonstrate driving-induced fragile topology in two different models, namely, the Floquet honeycomb model and the Floquet pi-flux square-lattice model. In both cases, we discover a rich phase diagram that includes Floquet fragile topological phases protected by crystalline rotation or mirror symmetries, Floquet Chern insulators, and trivial atomic phases, with distinct boundary features. Remarkably, the transitions between different phases can be feasibly achieved by simply tuning the driving amplitudes, which is a unique feature of driving-enabled topological phenomena. Moreover, corner-localized fractional charges are identified as a {\textquotedblleft}smoking-gun{\textquotedblright} signal of fragile topology in our systems. Our work paves the way for studying and realizing fragile topology in Floquet systems.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.103.L121115}, author = {Zhang, Rui-Xing and Yang, Zhi-Cheng} } @article {19321, title = {Tunable quantum interference using a topological source of indistinguishable photon pairs}, journal = {Nature Photonics}, year = {2021}, abstract = {Sources of quantum light, in particular correlated photon pairs that are indistinguishable for all degrees of freedom, are the fundamental resource for photonic quantum computation and simulation. Although such sources have been recently realized using integrated photonics, they offer limited ability to tune the spectral and temporal correlations between generated photons because they rely on a single component, such as a ring resonator. Here, we demonstrate a tunable source of indistinguishable photon pairs using dual-pump spontaneous four-wave mixing in a topological system comprising a two-dimensional array of resonators. We exploit the linear dispersion of the topological edge states to tune the spectral bandwidth (by about 3.5{\texttimes}), and thereby, to tune quantum interference between generated photons by tuning the two pump frequencies. We demonstrate energy-time entanglement and, using numerical simulations, confirm the topological robustness of our source. Our results could lead to tunable, frequency-multiplexed quantum light sources for photonic quantum technologies.

}, doi = {10.1038/s41566-021-00810-1}, url = {https://doi.org/10.1038/s41566-021-00810-1}, author = {Sunil Mittal and Venkata Vikram Orre and Elizabeth A. Goldschmidt and Mohammad Hafezi} } @article {19291, title = {Tunable Three-Body Loss in a Nonlinear Rydberg Medium}, journal = {Phys. Rev. Lett.}, volume = {126}, year = {2021}, month = {Apr}, pages = {173401}, abstract = {Long-range Rydberg interactions, in combination with electromagnetically induced transparency (EIT), give rise to strongly interacting photons where the strength, sign, and form of the interactions are widely tunable and controllable. Such control can be applied to both coherent and dissipative interactions, which provides the potential for generating novel few-photon states. Recently it has been shown that Rydberg-EIT is a rare system in which three-body interactions can be as strong or stronger than two-body interactions. In this work, we study three-body scattering loss for Rydberg-EIT in a wide regime of single and two-photon detunings. Our numerical simulations of the full three-body wave function and analytical estimates based on Fermi{\textquoteright}s golden rule strongly suggest that the observed features in the outgoing photonic correlations are caused by the resonant enhancement of the three-body losses.

}, doi = {10.1103/PhysRevLett.126.173401}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.126.173401}, author = {Ornelas-Huerta, D. P. and Bienias, Przemyslaw and Craddock, Alexander N. and Gullans, Michael J. and Hachtel, Andrew J. and Kalinowski, Marcin and Lyon, Mary E. and Gorshkov, Alexey V. and Rolston, S. L. and Porto, J. V.} } @article { WOS:000654369300061, title = {Two-beam coupling in the production of quantum correlated images by four-wave mixing}, journal = {Opt. Express}, volume = {29}, number = {11}, year = {2021}, month = {MAY 24}, pages = {16665-16675}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {We investigate the effect of 2-beam coupling in different imaging geometries in generating intensity-difference squeezing from four-wave mixing (4WM) in Rb atomic vapors. A recently-introduced dual-seeding technique can cancel out the classical noise in a seeded four-wave mixing process. This dual-seeding technique, however, can introduce new complications that involve 2-beam coupling between different seeded spatial modes in the atomic vapor and can ruin squeezing at frequencies on the order of the atomic linewidth and below. This complicates some forms of quantum imaging using these systems. Here we show that seeding the 4WM process with skew rays can eliminate the excess noise caused by 2-beam coupling. To avoid 2-beam coupling in bright, seeded images, it is important to re-image the object in the gain medium, instead of focussing through it. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement}, issn = {1094-4087}, doi = {10.1364/OE.424392}, author = {Wu, Meng-Chang and Brewer, Nicholas R. and Speirs, Rory W. and Jones, Kevin M. and Lett, Paul D.} } @article { WOS:000730391400013, title = {Ultra-broadband Kerr microcomb through soliton spectral translation}, journal = {Nat. Commun.}, volume = {12}, number = {1}, year = {2021}, month = {DEC 14}, publisher = {NATURE PORTFOLIO}, type = {Article}, abstract = {Broadband and low-noise microresonator frequency combs (microcombs) are critical for deployable optical frequency measurements. Here we expand the bandwidth of a microcomb far beyond its anomalous dispersion region on both sides of its spectrum through spectral translation mediated by mixing of a dissipative Kerr soliton and a secondary pump. We introduce the concept of synthetic dispersion to qualitatively capture the system{\textquoteright}s key physical behavior, in which the second pump enables spectral translation through four-wave mixing Bragg scattering. Experimentally, we pump a silicon nitride microring at 1063 nm and 1557 nm to enable soliton spectral translation, resulting in a total bandwidth of 1.6 octaves (137-407 THz). We examine the comb{\textquoteright}s low-noise characteristics, through heterodyne beat note measurements across its spectrum, measurements of the comb tooth spacing in its primary and spectrally translated portions, and their relative noise. These ultra-broadband microcombs provide new opportunities for optical frequency synthesis, optical atomic clocks, and reaching previously unattainable wavelengths. Integrated optical frequency measurements, benefit from broadband on-chip frequency combs. Here the authors present a low-noise microcomb whose span extends from telecom to near-visible wavelengths. Here the authors present a dissipative Kerr soliton formation approximated by introducing the concept of synthetic dispersion.}, doi = {10.1038/s41467-021-27469-0}, author = {Moille, Gregory and Perez, Edgar F. and Stone, Jordan R. and Rao, Ashutosh and Lu, Xiyuan and Rahman, Tahmid Sami and Chembo, Yanne K. and Srinivasan, Kartik} } @article {carney_ultralight_2021, title = {Ultralight dark matter detection with mechanical quantum sensors}, journal = {New J. Phys.}, volume = {23}, number = {2}, year = {2021}, note = {Place: TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND Publisher: IOP PUBLISHING LTD Type: Article}, month = {feb}, abstract = {We consider the use of quantum-limited mechanical force sensors to detect ultralight (sub-meV) dark matter (DM) candidates which are weakly coupled to the standard model. We show that mechanical sensors with masses around or below the milligram scale, operating around the standard quantum limit, would enable novel searches for DM with natural frequencies around the kHz scale. This would complement existing strategies based on torsion balances, atom interferometers, and atomic clock systems.}, keywords = {dark matter, Optomechanics, quantum sensing}, issn = {1367-2630}, doi = {10.1088/1367-2630/abd9e7}, author = {Carney, Daniel and Hook, Anson and Liu, Zhen and Taylor, Jacob M. and Zhao, Yue} } @article { WOS:000665117900005, title = {Universal stereodynamics of cold atom-molecule collisions in electric fields}, journal = {Phys. Rev. A}, volume = {103}, number = {6}, year = {2021}, month = {JUN 23}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We use numerically exact quantum dynamics calculations to demonstrate universal stereoselectivity of cold collisions of (2)Pi molecules with S-1-state atoms in an external electric field. We show that cold collisions of OH molecules in their low-field-seeking f-states, whose dipole moments are oriented against the field direction, are much more likely to lead to inelastic scattering than those of molecules oriented along the field direction, causing nearly perfect steric asymmetry in the inelastic collision cross sections. The universal nature of this effect is due to the threshold suppression of inelastic scattering between the degenerate +/- M Stark sublevels of the high-field-seeking e-state, where M is the projection of the total angular momentum of the molecule on the field axis. Above the Lambda-doublet threshold, the stereodynamics of inelastic atom-molecule collisions can be tuned via electric-field-induced resonances, which enable effective control of Ne + OH scattering over the range of collision energies achievable in current merged beam experiments.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.103.062810}, author = {Tscherbul, V, Timur and Klos, Jacek} } @article { WOS:000686926200001, title = {Using an Atom Interferometer to Infer Gravitational Entanglement Generation}, journal = {PRX Quantum}, volume = {2}, number = {3}, year = {2021}, month = {AUG 18}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {If gravitational perturbations are quantized into gravitons in analogy with the electromagnetic field and photons, the resulting graviton interactions should lead to an entangling interaction between massive objects. We suggest a test of this prediction. To do this, we introduce the concept of interactive quantum information sensing. This novel sensing protocol is tailored to provable verification of weak dynamical entanglement generation between a pair of systems. We show that this protocol is highly robust to typical thermal noise sources. Moreover, the sensitivity can be increased both using an initial thermal state and/or an initial phase of entangling via a nongravitational interaction. We outline a concrete implementation testing the ability of the gravitational field to generate entanglement between an atomic interferometer and a mechanical oscillator. Preliminary numerical estimates suggest that near-term devices could feasibly be used to perform the experiment.}, doi = {10.1103/PRXQuantum.2.030330}, author = {Carney, Daniel and Muller, Holger and Taylor, Jacob M.} } @article {zhang_van_2021, title = {Van der {Waals} heterostructure polaritons with moire-induced nonlinearity}, journal = {Nature}, volume = {591}, number = {7848}, year = {2021}, note = {Place: HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY Publisher: NATURE RESEARCH Type: Article}, month = {mar}, pages = {61+}, abstract = {Controlling matter-light interactions with cavities is of fundamental importance in modern science and technology(1). This is exemplified in the strong-coupling regime, where matter-light hybrid modes form, with properties that are controllable by optical-wavelength photons(2,3). By contrast, matter excitations on the nanometre scale are harder to access. In two-dimensional van der Waals heterostructures, a tunable moire lattice potential for electronic excitations may form(4), enabling the generation of correlated electron gases in the lattice potentials(5-9). Excitons confined in moire lattices have also been reported(10,11), but no cooperative effects have been observed and interactions with light have remained perturbative(12-15). Here, by integrating MoSe2-WS2 heterobilayers in a microcavity, we establish cooperative coupling between moire-lattice excitons and microcavity photons up to the temperature of liquid nitrogen, thereby integrating versatile control of both matter and light into one platform. The density dependence of the moire polaritons reveals strong nonlinearity due to exciton blockade, suppressed exciton energy shift and suppressed excitation-induced dephasing, all of which are consistent with the quantum confined nature of the moire excitons. Such a moire polariton system combines strong nonlinearity and microscopic-scale tuning of matter excitations using cavity engineering and long-range light coherence, providing a platform with which to study collective phenomena from tunable arrays of quantum emitters.}, issn = {0028-0836}, doi = {10.1038/s41586-021-03228-5}, author = {Zhang, Long and Wu, Fengcheng and Hou, Shaocong and Zhang, Zhe and Chou, Yu-Hsun and Watanabe, Kenji and Taniguchi, Takashi and Forrest, Stephen R. and Deng, Hui} } @article { WOS:000723456200001, title = {Weyl Curvature Hypothesis in Light of Quantum Backreaction at Cosmological Singularities or Bounces}, journal = {Universe}, volume = {07}, number = {11}, year = {2021}, month = {NOV}, publisher = {MDPI}, type = {Review}, abstract = {The Weyl curvature constitutes the radiative sector of the Riemann curvature tensor and gives a measure of the anisotropy and inhomogeneities of spacetime. Penrose{\textquoteright}s 1979 Weyl curvature hypothesis (WCH) assumes that the universe began at a very low gravitational entropy state, corresponding to zero Weyl curvature, namely, the Friedmann-Lemaitre-Robertson-Walker (FLRW) universe. This is a simple assumption with far-reaching implications. In classical general relativity, Belinsky, Khalatnikov and Lifshitz (BKL) showed in the 70s that the most general cosmological solutions of the Einstein equation are that of the inhomogeneous Kasner types, with intermittent alteration of the one direction of contraction (in the cosmological expansion phase), according to the mixmaster dynamics of Misner (M). How could WCH and BKL-M co-exist? An answer was provided in the 80s with the consideration of quantum field processes such as vacuum particle creation, which was copious at the Planck time ( 10 - 43 s), and their backreaction effects were shown to be so powerful as to rapidly damp away the irregularities in the geometry. It was proposed that the vaccum viscosity due to particle creation can act as an efficient transducer of gravitational entropy (large for BKL-M) to matter entropy, keeping the universe at that very early time in a state commensurate with the WCH. In this essay I expand the scope of that inquiry to a broader range, asking how the WCH would fare with various cosmological theories, from classical to semiclassical to quantum, focusing on their predictions near the cosmological singularities (past and future) or avoidance thereof, allowing the Universe to encounter different scenarios, such as undergoing a phase transition or a bounce. WCH is of special importance to cyclic cosmologies, because any slight irregularity toward the end of one cycle will generate greater anisotropy and inhomogeneities in the next cycle. We point out that regardless of what other processes may be present near the beginning and the end states of the universe, the backreaction effects of quantum field processes probably serve as the best guarantor of WCH because these vacuum processes are ubiquitous, powerful and efficient in dissipating the irregularities to effectively nudge the Universe to a near-zero Weyl curvature condition.}, keywords = {backreaction effects, cyclic universe, early universe cosmology, quantum fields, singularity and bounce, weyl curvature hypothesis}, doi = {10.3390/universe7110424}, author = {Hu, Bei-Lok} } @article { WOS:000744184400009, title = {Which Way Does Stimulated Emission Go?}, journal = {J. Phys. Chem. A}, volume = {125}, number = {50}, year = {2021}, month = {DEC 23}, pages = {10667-10676}, publisher = {AMER CHEMICAL SOC}, type = {Article}, abstract = {Is it possible to form an image using light produced by stimulated emission? Here we study light scatter off an assembly of excited chromophores. Due to the Optical Theorem, stimulated emission is necessarily accompanied by excited state Rayleigh scattering. Both processes can be used to form images, though they have different dependencies on scattering direction, wavelength and chromophore configuration. Our results suggest several new approaches to optical imaging using fluorophore excited states.}, issn = {1089-5639}, doi = {10.1021/acs.jpca.1c07713}, author = {Wong-Campos, J. David and Porto, V, J. and Cohen, Adam E.} } @article { WOS:000702389700001, title = {Wilson loop and Wilczek-Zee phase from a non-Abelian gauge field}, journal = {npj Quantum Inform.}, volume = {7}, number = {1}, year = {2021}, month = {SEP 30}, publisher = {NATURE PORTFOLIO}, type = {Article}, abstract = {Quantum states can acquire a geometric phase called the Berry phase after adiabatically traversing a closed loop, which depends on the path not the rate of motion. The Berry phase is analogous to the Aharonov-Bohm phase derived from the electromagnetic vector potential, and can be expressed in terms of an Abelian gauge potential called the Berry connection. Wilczek and Zee extended this concept to include non-Abelian phases-characterized by the gauge-independent Wilson loop-resulting from non-Abelian gauge potentials. Using an atomic Bose-Einstein condensate, we quantum-engineered a non-Abelian SU(2) gauge field, generated by a Yang monopole located at the origin of a 5-dimensional parameter space. By slowly encircling the monopole, we characterized the Wilczek-Zee phase in terms of the Wilson loop, that depended on the solid-angle subtended by the encircling path: a generalization of Stokes{\textquoteright} theorem. This observation marks the observation of the Wilson loop resulting from a non-Abelian point source.}, doi = {10.1038/s41534-021-00483-2}, author = {Sugawa, Seiji and Salces-Carcoba, Francisco and Yue, Yuchen and Putra, Andika and Spielman, I. B.} } @article { WOS:000707473300010, title = {Yang-Lee edge singularity triggered entanglement transition}, journal = {Phys. Rev. B}, volume = {104}, number = {16}, year = {2021}, month = {OCT 11}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We show that a class of PT symmetric non-Hermitian Hamiltonians realizing the Yang-Lee edge singularity exhibits an entanglement transition in the long-time steady state evolved under the Hamiltonian. Such a transition is induced by a level crossing triggered by the critical point associated with the Yang-Lee singularity and hence is first order in nature. At the transition, the entanglement entropy of the steady state jumps discontinuously from a volume-law to an area-law scaling. We exemplify this mechanism using a one-dimensional transverse field Ising model with additional imaginary fields, as well as the spin-1 Blume-Capel model and the three-state Potts model. We further make a connection to the forced-measurement induced entanglement transition in a Floquet nonunitary circuit subject to continuous measurements followed by post-selections. Our results demonstrate a new mechanism for entanglement transitions in non-Hermitian systems harboring a critical point.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.104.L161107}, author = {Jian, Shao-Kai and Yang, Zhi-Cheng and Bi, Zhen and Chen, Xiao} } @article { WOS:000688493300002, title = {Z(2) topological order and first-order quantum phase transitions in systems with combinatorial gauge symmetry}, journal = {Phys. Rev. B}, volume = {104}, number = {8}, year = {2021}, month = {AUG 24}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study a generalization of the two-dimensional transverse-field Ising model, combining both ferromagnetic and antiferromagnetic two-body interactions, that hosts exact global and local Z(2) gauge symmetries. Using exact diagonalization and stochastic series expansion quantum Monte Carlo methods, we confirm the existence of the topological phase in line with previous theoretical predictions. Our simulation results show that the transition between the confined topological phase and the deconfined paramagnetic phase is of first order, in contrast to the conventional Z(2) lattice gauge model in which the transition maps onto that of the standard Ising model and is continuous. We further generalize the model by replacing the transverse field on the gauge spins with a ferromagnetic XX interaction while keeping the local gauge symmetry intact. We find that the Z(2) topological phase remains stable, while the paramagnetic phase is replaced by a ferromagnetic phase. The topological-ferromagnetic quantum phase transition is also of first order. For both models, we discuss the low-energy spinon and vison excitations of the topological phase and their avoided level crossings associated with the first-order quantum phase transitions.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.104.085145}, author = {Wu, Kai-Hsin and Yang, Zhi-Cheng and Green, Dmitry and Sandvik, Anders W. and Chamon, Claudio} } @article { WOS:000685127300001, title = {Z(3) Quantum Double in a Superconducting Wire Array}, journal = {PRX Quantum}, volume = {2}, number = {3}, year = {2021}, month = {AUG 13}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We show that a Z(3) quantum double can be realized in an array of superconducting wires coupled via Josephson junctions. With a suitably chosen magnetic flux threading the system, the interwire Josephson couplings take the form of a complex Hadamard matrix, which possesses combinatorial gauge symmetry-a local Z(3) symmetry involving permutations and shifts by +/- 2 pi/3 of the superconducting phases. The sign of the star potential resulting from the Josephson energy is inverted in this physical realization, leading to a massive degeneracy in the nonzero flux sectors. A dimerization pattern encoded in the capacitances of the array lifts up these degeneracies, resulting in a Z(3) topologically ordered state. Moreover, this dimerization pattern leads to a larger effective vison gap as compared to the canonical case with the usual (uninverted) star term. We further show that our model maps to a quantum three-state Potts model under a duality transformation. We argue, using a combination of bosonization and mean field theory, that altering the dimerization pattern of the capacitances leads to a transition from the Z(3) topological phase into a quantum XY-ordered phase. Our work highlights that combinatorial gauge symmetry can serve as a design principle to build quantum double models using systems with realistic interactions.}, doi = {10.1103/PRXQuantum.2.030327}, author = {Yang, Zhi-Cheng and Green, Dmitry and Yu, Hongji and Chamon, Claudio} } @article { WOS:000649079900009, title = {Zeroth law in quantum thermodynamics at strong coupling: In equilibrium, not at equal temperature}, journal = {Phys. Rev. D}, volume = {103}, number = {8}, year = {2021}, month = {APR 13}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The zeroth law of thermodynamics involves a transitivity relation (pairwise between three objects) expressed either in terms of {\textquoteleft}{\textquoteleft}equal temperature{{\textquoteright}{\textquoteright}} (ET), or {\textquoteleft}{\textquoteleft}in equilibrium{{\textquoteright}{\textquoteright}} (EQ) conditions. In conventional thermodynamics conditional on vanishingly weak system-bath coupling these two conditions are commonly regarded as equivalent. In this work we show that for thermodynamics at strong coupling they are inequivalent: namely, two systems can he in equilibrium and yet have different effective temperatures. A recent result {[}J.-T. Hsiang and B. L. Hu, Phys. Rev. D 103, 065001 (2021) for Gaussian quantum systems shows that an effective temperature r can be defined at all times during a system{\textquoteright}s nonequilibrium evolution, but because of the inclusion of interaction energy, after equilibration the system{\textquoteright}s T{*} is slightly higher than the bath temperature T-B, with the deviation depending on the coupling. A second object coupled with a different strength with an identical bath at temperature T-B will not have the same equilibrated temperature as the first object. Thus ET not equal EQ for strong coupling thermodynamics. We then investigate the conditions for dynamical equilibration for two objects 1 and 2 strongly coupled with a common bath B, each with a different equilibrated effective temperature. We show this is possible, and prove the existence of a generalized fluctuation-dissipation relation under this configuration. This affirms that in equilibrium is a valid and perhaps more fundamental notion which the zeroth law for quantum thermodynamics at strong coupling should be based on. Only when the system-bath coupling becomes vanishingly weak that {\textquoteleft}{\textquoteleft}temperature{{\textquoteright}{\textquoteright}} appearing in thermodynamic relations becomes universally defined and makes better physical sense.}, issn = {2470-0010}, doi = {10.1103/PhysRevD.103.085004}, author = {Hsiang, Jen-Tsung and Hu, Bei-Lok} } @article {huang_4d_2020, title = {{4D} beyond-cohomology topological phase protected by {C}-2 symmetry and its boundary theories}, journal = {Phys. Rev. Res.}, volume = {2}, number = {3}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {aug}, abstract = {We study bosonic symmetry-protected topological (SPT) phases with C-2 rotational symmetry in four spatial dimensions which is not captured by the group cohomology classification. By using the topological crystal approach, we show that the topological crystalline state of this SPT phase is given by placing an E-8 state on the two-dimensional rotational invariant plane, which provides a simple physical picture of this phase. Based on this understanding, we show that a variant of QED in four dimensions (QED(4)) with charge-1 and charge-3 Dirac fermions is a field theoretical description of the three-dimensional boundary. We also discuss the connection to a symmetric gapped boundary with topological order and its anomalous signature.

}, doi = {10.1103/PhysRevResearch.2.033236}, author = {Huang, Sheng-Jie} } @article {bulmash_absolute_2020, title = {Absolute anomalies in (2+1){D} symmetry-enriched topological states and exact (3+1){D} constructions}, journal = {Phys. Rev. Res.}, volume = {2}, number = {4}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {oct}, abstract = {Certain patterns of symmetry fractionalization in (2+1)-dimensional [(2+1)D] topologically ordered phases of matter can be anomalous, which means that they possess an obstruction to being realized in purely (2+1)D. In this paper we demonstrate how to compute the anomaly for symmetry-enriched topological states of bosons in complete generality. We demonstrate how, given any unitary modular tensor category (UMTC) and symmetry fractionalization class for a global symmetry group G, one can define a (3+1)-dimensional [(3+1)D] topologically invariant path integral in terms of a state sum for a G-symmetry-protected topological (SPT) state. We present an exactly solvable Hamiltonian for the system and demonstrate explicitly a (2+1)D G-symmetric surface termination that hosts deconfined anyon excitations described by the given UMTC and symmetry fractionalization class. We present concrete algorithms that can be used to compute anomaly indicators in general. Our approach applies to general symmetry groups, including anyon-permuting and antiunitary symmetries. In addition to providing a general way to compute the anomaly, our result also shows, by explicit construction, that every symmetry fractionalization class for any UMTC can be realized at the surface of a (3+1)D SPT state. As a by-product, this construction also provides a way of explicitly seeing how the algebraic data that defines symmetry fractionalization in general arises in the context of exactly solvable models. In the case of unitary orientation-preserving symmetries, our results can also be viewed as providing a method to compute the H-4(G, U(1)) obstruction that arises in the theory of G-crossed braided tensor categories, for which no general method has been presented to date.}, doi = {10.1103/PhysRevResearch.2.043033}, author = {Bulmash, Daniel and Barkeshli, Maissam} } @article { ISI:000513256600002, title = {Accessing ratios of quantized resistances in graphene p-n junction devices using multiple terminals}, journal = {AIP Adv.}, volume = {10}, number = {2}, year = {2020}, month = {FEB 1}, pages = {025112}, publisher = {AMER INST PHYSICS}, type = {Article}, abstract = {The utilization of multiple current terminals on millimeter-scale graphene p-n junction devices has enabled the measurement of many atypical, fractional multiples of the quantized Hall resistance at the v = 2 plateau (R-H approximate to 12 906 Omega). These fractions take the form a/bR(H) and can be determined both analytically and by simulations. These experiments validate the use of either the LTspice circuit simulator or the analytical framework recently presented in similar work. Furthermore, the production of several devices with large-scale junctions substantiates the approach of using simple ultraviolet lithography to obtain junctions of sufficient sharpness. (C) 2020 Author(s).}, doi = {10.1063/1.5138901}, author = {Patel, Dinesh and Marzano, Martina and Liu, I, Chieh- and Hill, Heather M. and Kruskopf, Mattias and Jin, Hanbyul and Hu, Jiuning and Newell, David B. and Liang, Chi-Te and Elmquist, Randolph and Rigosi, Albert F.} } @article { ISI:000528518000008, title = {Accurate Prediction of Clock Transitions in a Highly Charged Ion with Complex Electronic Structure}, journal = {Phys. Rev. Lett.}, volume = {124}, number = {16}, year = {2020}, month = {APR 24}, pages = {163001}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We develop a broadly applicable approach that drastically increases the ability to predict the properties of complex atoms accurately. We apply it to the case of Ir-17(+), which is of particular interest for the development of novel atomic clocks with a high sensitivity to the variation of the fine-structure constant and to dark matter searches. In general, clock transitions are weak and very difficult to identify without accurate theoretical predictions. In the case of Ir-17(+), even stronger electric-dipole (El) transitions have eluded observation despite years of effort, raising the possibility that the theoretical predictions are grossly wrong. In this work, we provide accurate predictions of the transition wavelengths and E1 transition rates for Ir-17(+). Our results explain the lack of observations of the E1 transitions and provide a pathway toward the detection of clock transitions. The computational advances we demonstrate in this work are widely applicable to most elements in the periodic table and will allow us to solve numerous problems in atomic physics, astrophysics, and plasma physics.

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.124.163001}, author = {Cheung, C. and Safronova, M. S. and Porsev, S. G. and Kozlov, M. G. and Tupitsyn, I. I. and Bondarev, I. A.} } @article { ISI:000533306300001, title = {Analysing quantized resistance behaviour in graphene Corbino p-n junction devices}, journal = {J. Phys. D-Appl. Phys.}, volume = {53}, number = {27}, year = {2020}, month = {JUL 1}, pages = {275301}, publisher = {IOP PUBLISHING LTD}, type = {Article}, abstract = {Just a few of the promising applications of graphene Corbino pnJ devices include two-dimensional Dirac fermion microscopes, custom programmable quantized resistors, and mesoscopic valley filters. In some cases, device scalability is crucial, as seen in fields like resistance metrology, where graphene devices are required to accommodate currents of the order 100 mu A to be compatible with existing infrastructure. However, fabrication of these devices still poses many difficulties. In this work, unusual quantized resistances are observed in epitaxial graphene Corbino p-n junction devices held at the nu=2We present a theoretical study of single-particle and many-body properties of twisted bilayer WSe2. For single-particle physics, we calculate the band topological phase diagram and electron local density of states (LDOS), which are found to be correlated. By comparing our theoretical LDOS with those measured by scanning tunneling microscopy, we comment on the possible topological nature of the first moire valence band. For many-body physics, we construct a generalized Hubbard model on a triangular lattice based on the calculated single-particle moire bands. We show that a layer potential difference, arising, for example, from an applied electric field, can drastically change the noninteracting moire bands, tune the spin-orbit coupling in the Hubbard model, control the charge excitation gap of the Mott insulator at half-filling, and generate an effective Dzyaloshinskii-Moriya interaction in the effective Heisenberg model for the Mott insulator. Our theoretical results agree with transport experiments on the same system in several key aspects, and establish twisted bilayer WSe2 as a highly tunable system for studying and simulating strongly correlated phenomena in the Hubbard model.

}, doi = {10.1103/PhysRevResearch.2.033087}, author = {Pan, Haining and Wu, Fengcheng and Das Sarma, Sankar} } @article { ISI:000570300500002, title = {Beyond spontaneous emission: Giant atom bounded in the continuum}, journal = {Phys. Rev. A}, volume = {102}, number = {3}, year = {2020}, month = {SEP 8}, pages = {033706}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The quantum coupling of individual superconducting qubits to microwave photons leads to remarkable experimental opportunities. Here we consider the phononic case where the qubit is coupled to an electromagnetic surface acoustic wave antenna that enables supersonic (electromagnetic) propagation of the qubit oscillations. This can be considered as a giant atom that is many phonon wavelengths long. We study an exactly solvable toy model that captures these effects, and find that this non-Markovian giant atom has a suppressed relaxation, so long as an effective vacuum coupling exists between a qubit excitation and a localized wave packet of sound, even in the absence of a cavity for the sound waves. Finally, we consider practical implementations of these ideas in current surface acoustic wave devices.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.102.033706}, author = {Guo, Shangjie and Wang, Yidan and Purdy, Thomas and Taylor, Jacob} } @article { ISI:000565826800008, title = {Braiding photonic topological zero modes}, journal = {Nat. Phys.}, volume = {16}, number = {9}, year = {2020}, month = {SEP}, pages = {989+}, publisher = {NATURE PUBLISHING GROUP}, type = {Article}, abstract = {A remarkable property of quantum mechanics in two-dimensional space is its ability to support {\textquoteleft}anyons{\textquoteright}, particles that are neither fermions nor bosons. Theory predicts that these exotic excitations can exist as bound states confined near topological defects, such as Majorana zero modes trapped in vortices in topological superconductors. Intriguingly, in the simplest cases the non-trivial phase that arises when such defects are {\textquoteleft}braided{\textquoteright} around one another is not intrinsically quantum mechanical; instead, it can be viewed as a manifestation of the geometric (Pancharatnam-Berry) phase in wave mechanics, which makes possible the simulation of such phenomena in classical systems. Here, we report the experimental measurement of the geometric phase owing to such a braiding process. These measurements are obtained with an interferometer constructed from highly tunable two-dimensional arrays of photonic waveguides. Our results introduce photonic lattices as a versatile platform for the experimental study of topological defects and their braiding, and complement ongoing efforts in the study of solid-state systems and cold atomic gases. The non-zero geometric phase acquired by the braiding of vortex modes in photonic waveguide lattices demonstrates their potential to serve as a platform for the study of both Abelian and non-Abelian braiding in bosonic systems.}, issn = {1745-2473}, doi = {10.1038/s41567-020-1007-5},}, author = {Noh, Jiho and Schuster, Thomas and Iadecola, Thomas and Huang, Sheng and Wang, Mohan and Chen, Kevin P. and Chamon, Claudio and Rechtsman, Mikael C.} } @article {zhang_branching_2020, title = {Branching fractions for {P}-3/2 decays in {Ba}+}, journal = {Phys. Rev. A}, volume = {101}, number = {6}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {jun}, abstract = {Branching fractions for decays from the P-3/2 level in B-138 at have been measured with a single laser-cooled ion. Decay probabilities to S-1/2, D-3/2, and D-5/2 are determined to be 0.741716(71), 0.028031(23), and 0.230253(61), respectively, which are an order-of-magnitude improvement over previous results. Our methodology only involves optical pumping and state detection, and is hence relatively free of systematic effects. Measurements are carried out in two different ways to check for consistency. Our analysis also includes a measurement of the D-5/2 lifetime, for which we obtain 30.14(40) s.}, issn = {1050-2947}, doi = {10.1103/PhysRevA.101.062515}, author = {Zhang, Zhiqiang and Arnold, K. J. and Chanu, S. R. and Kaewuam, R. and Safronova, M. S. and Barrett, M. D.} } @article { ISI:000548140000001, title = {Branching fractions for P-3/2 decays in Ba+}, journal = {Phys. Rev. A}, volume = {101}, number = {6}, year = {2020}, month = {JUN 24}, pages = {062515}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Branching fractions for decays from the P-3/2 level in B-138 at have been measured with a single laser-cooled ion. Decay probabilities to S-1/2, D-3/2, and D-5/2 are determined to be 0.741716(71), 0.028031(23), and 0.230253(61), respectively, which are an order-of-magnitude improvement over previous results. Our methodology only involves optical pumping and state detection, and is hence relatively free of systematic effects. Measurements are carried out in two different ways to check for consistency. Our analysis also includes a measurement of the D-5/2 lifetime, for which we obtain 30.14(40) s.}, issn = {1050-2947}, doi = {10.1103/PhysRevA.101.062515}, author = {Zhang, Zhiqiang and Arnold, K. J. and Chanu, S. R. and Kaewuam, R. and Safronova, M. S. and Barrett, M. D.} } @article {moille_broadband_2020, title = {Broadband resonator-waveguide coupling for efficient extraction of octave-spanning microcombs}, journal = {Opt. Lett.}, volume = {45}, number = {17}, year = {2020}, note = {Place: 2010 MASSACHUSETTS AVE NW, WASHINGTON, DC 20036 USA Publisher: OPTICAL SOC AMER Type: Correction}, month = {sep}, pages = {4939}, issn = {0146-9592}, doi = {10.1364/OL.405775}, author = {Moille, Gregory and Li, Qing and Briles, Travis C. and Yu, Su-Peng and Drake, Tara and Lu, Xiyuan and Rao, Ashutosh and Westly, Daron and Papp, Scott B. and Srinivasan, Kartik} } @article { ISI:000550674500006, title = {Calculation of higher-order corrections to the light shift of the 5s(2) S-1(0)-5s5p P-3(0)o clock transition in Cd}, journal = {Phys. Rev. A}, volume = {102}, number = {1}, year = {2020}, month = {JUL 20}, pages = {012811}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {In the recent work by Yamaguchi et al. {[}Phys. Rev. Lett. 123, 113201 (2019)] Cd was identified as an excellent candidate for a lattice clock. Here, we carried out computations needed for further clock development and made an assessment of the higher-order corrections to the light shift of the 5s(2) S-1(0) -5s5p P-3(0)o clock transition. We carried out calculations of the magnetic dipole and electric quadrupole polarizabilities and linear and circular hyperpolarizabilities of the 5s(2) S-1(0) and 5s5p P-3(0)o clock states at the magic wavelength and estimated uncertainties of these quantities. We also evaluated the second-order Zeeman clock transition frequency shift.}, issn = {1050-2947}, doi = {10.1103/PhysRevA.102.012811}, author = {Porsev, S. G. and Safronova, M. S.} } @article {raines_cavity_2020, title = {Cavity {Higgs} polaritons}, journal = {Phys. Rev. Res.}, volume = {2}, number = {1}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {feb}, abstract = {Motivated by the dramatic success of realizing cavity exciton-polariton condensation in experiment we consider the formation of polaritons from cavity photons and the amplitude or Higgs mode of a superconductor. Enabled by the recently predicted and observed supercurrent-induced linear coupling between these excitations and light, we find that hybridization between Higgs excitations in a disordered quasi-2D superconductor and resonant cavity photons can occur, forming Higgs-polariton states. This provides the potential for a new means to manipulate the superconducting state as well as the potential for novel photonic cavity circuit elements.}, doi = {10.1103/PhysRevResearch.2.013143}, author = {Raines, Zachary M. and Allocca, Andrew A. and Hafezi, Mohammad and Galitski, Victor M.} } @conference {barik_chiral_2020-1, title = {Chiral coupling of a quantum emitter in a topological photonic resonator}, booktitle = {2020 Conference on Lasers and Electro-Optics (CLEO)}, series = {Conference on {Lasers} and {Electro}-{Optics}}, year = {2020}, note = {Backup Publisher: IEEE ISSN: 2160-9020 Type: Proceedings Paper}, publisher = {IEEE}, organization = {IEEE}, address = {345 E 47TH ST, NEW YORK, NY 10017 USA}, abstract = {Here we demonstrate chiral light-matter interactions in a topological photonic crystal resonator. We achieve this by employing valley-Hall topological edge states to create a helical resonator at the interface of two topologically distinct regions. (C) 2020 The Author(s)

}, isbn = {978-1-943580-76-7}, author = {Barik, Sabyasachi and Karasahin, Aziz and Mittal, Sunil and Hafezi, Mohammad and Waks, Edo} } @article { ISI:000531732200005, title = {Chiral quantum optics using a topological resonator}, journal = {Phys. Rev. B}, volume = {101}, number = {20}, year = {2020}, month = {MAY 12}, pages = {205303}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Chiral nanophotonic components, such as waveguides and resonators coupled to quantum emitters, provide a fundamentally new approach to manipulate light-matter interactions. The recent emergence of topological photonics has provided a new paradigm to realize helical/chiral nanophotonic structures that are flexible in design and, at the same time, robust against sharp bends and disorder. Here we demonstrate such a topologically protected chiral nanophotonic resonator that is strongly coupled to a solid-state quantum emitter. Specifically, we employ the valley-Hall effect in a photonic crystal to achieve topological edge states at an interface between two topologically distinct regions. Our helical resonator supports two counterpropagating edge modes with opposite polarizations. We first show chiral coupling between the topological resonator and the quantum emitter such that the emitter emits preferably into one of the counterpropagating edge modes depending upon its spin. Subsequently, we demonstrate strong coupling between the resonator and the quantum emitter using resonant Purcell enhancement in the emission intensity by a factor of 3.4. Such chiral resonators could enable designing complex nanophotonic circuits for quantum information processing and studying novel quantum many-body dynamics.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.101.205303}, author = {Barik, Sabyasachi and Karasahin, Aziz and Mittal, Sunil and Waks, Edo and Hafezi, Mohammad} } @article {liu_circuit_2020, title = {Circuit complexity across a topological phase transition}, journal = {Phys. Rev. Res.}, volume = {2}, number = {1}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {mar}, abstract = {We use Nielsen{\textquoteright}s geometric approach to quantify the circuit complexity in a one-dimensional Kitaev chain across a topological phase transition. We find that the circuit complexities of both the ground states and nonequilibrium steady states of the Kitaev model exhibit nonanalytical behaviors at the critical points, and thus can be used to detect both equilibrium and dynamical topological phase transitions. Moreover, we show that the locality property of the real-space optimal Hamiltonian connecting two different ground states depends crucially on whether the two states belong to the same or different phases. This provides a concrete example of classifying different gapped phases using Nielsen{\textquoteright}s circuit complexity. We further generalize our results to a Kitaev chain with long-range pairing, and we discuss generalizations to higher dimensions. Our result opens up an avenue for using circuit complexity as a tool to understand quantum many-body systems.}, doi = {10.1103/PhysRevResearch.2.013323}, author = {Liu, Fangli and Whitsitt, Seth and Curtis, Jonathan B. and Lundgren, Rex and Titum, Paraj and Yang, Zhi-Cheng and Garrison, James R. and Gorshkov, V, Alexey} } @article { ISI:000564912400007, title = {Coherent optical nanotweezers for ultracold atoms}, journal = {Phys. Rev. A}, volume = {102}, number = {1}, year = {2020}, month = {JUL 7}, pages = {013306}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {There has been a recent surge of interest and progress in creating subwavelength free-space optical potentials for ultracold atoms. A key open question is whether geometric potentials, which are repulsive and ubiquitous in the creation of subwavelength free-space potentials, forbid the creation of narrow traps with long lifetimes. Here, we show that it is possible to create such traps. We propose two schemes for realizing subwavelength traps and demonstrate their superiority over existing proposals. We analyze the lifetime of atoms in such traps and show that long-lived bound states are possible. This work allows for subwavelength control and manipulation of ultracold matter, with applications in quantum chemistry and quantum simulation.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.102.013306}, author = {Bienias, P. and Subhankar, S. and Wang, Y. and Tsui, T-C and Jendrzejewski, F. and Tiecke, T. and Juzeliunas, G. and Jiang, L. and Rolston, S. L. and Porto, V, J. and Gorshkov, V, A.} } @article { ISI:000510176900007, title = {Collective Excitations of Quantum Anomalous Hall Ferromagnets in Twisted Bilayer Graphene}, journal = {Phys. Rev. Lett.}, volume = {124}, number = {4}, year = {2020}, month = {JAN 30}, pages = {046403}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We present a microscopic theory for collective excitations of quantum anomalous Hall ferromagnets (QAHF) in twisted bilayer graphene. We calculate the spin magnon and valley magnon spectra by solving Bethe-Salpeter equations and verify the stability of QAHF. We extract the spin stiffness from the gapless spin wave dispersion and estimate the energy cost of a skyrmion-antiskyrmion pair, which is found to be comparable in energy with the Hartree-Fock gap. The valley wave mode is gapped, implying that the valley polarized state is more favorable compared to the valley coherent state. Using a nonlinear sigma model, we estimate the valley ordering temperature, which is considerably reduced from the mean-field transition temperature due to thermal excitations of valley waves.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.124.046403}, author = {Wu, Fengcheng and Das Sarma, Sankar} } @article {vu_collective_2020, title = {Collective ground states in small lattices of coupled quantum dots}, journal = {Phys. Rev. Res.}, volume = {2}, number = {2}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {apr}, abstract = {Motivated by recent developments on the fabrication and control of semiconductor-based quantum dots, we theoretically study a finite system of tunnel-coupled quantum dots with the electrons interacting through the long-range Coulomb interaction. When the interelectron separation is large and the quantum dot confinement potential is weak, the system behaves as an effective Wigner crystal with a period determined by the electron average density with considerable electron hopping throughout the system. For stronger periodic confinement potentials, however, the system makes a crossover to a Mott-type ground state where the electrons are completely localized at the individual dots with little interdot tunneling. In between these two phases, the system is essentially a strongly correlated electron liquid with intersite electron hopping constrained by strong Coulomb interaction. We characterize this Wigner-Mott-liquid quantum crossover with detailed numerical finite-size diagonalization calculations of the coupled interacting quantum dot system, showing that these phases can be smoothly connected by tuning the system parameters. Experimental feasibility of observing such a hopping-tuned Wigner-Mott-liquid crossover in currently available semiconductor quantum dots is discussed. In particular, we connect our theoretical results to recent quantum-dot-based quantum emulation experiments where a collective Coulomb blockade was demonstrated. We discuss realistic disorder effects on our theoretical findings. One conclusion of our work is that experiments must explore lower density quantum dot arrays in order to clearly observe the Wigner phase although the Mott-liquid crossover phenomenon should already manifest itself in the currently available quantum dot arrays. We also suggest a direct experimental electron density probe, such as atomic force microscopy or scanning tunneling microscopy, for a clear observation of the effective Wigner crystal phase.

}, doi = {10.1103/PhysRevResearch.2.023060}, author = {Vu, DinhDuy and Das Sarma, Sankar} } @article { ISI:000505979700006, title = {Collisions of room-temperature helium with ultracold lithium and the van der Waals bound state of HeLi}, journal = {Phys. Rev. A}, volume = {101}, number = {1}, year = {2020}, month = {JAN 6}, pages = {012702}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We have computed the thermally averaged total, elastic rate coefficient for the collision of a room-temperature helium atom with an ultracold lithium atom. This rate coefficient has been computed as part of the characterization of a cold-atom vacuum sensor based on laser-cooled Li-6 or Li-7 atoms that will operate in the ultrahigh-vacuum (p < 10(-6) Pa) and extreme-high-vacuum (p < 10(-10) Pa) regimes. The analysis involves computing the X (2) Sigma(+) HeLi Born-Oppenheimer potential followed by the numerical solution of the relevant radial Schrodinger equation. The potential is computed using a single-reference-coupled-cluster electronic-structure method with basis sets of different completeness in order to characterize our uncertainty budget. We predict that the rate coefficient for a 300 K helium gas and a 1 mu K Li gas is 1.467(13) x 10(-9) cm(3)/s for He-4 + Li-6 and 1.471(13) x 10(-9) cm(3)/s for He-4 + Li-7, where the numbers in parentheses are the one-standard-deviation uncertainties in the last two significant digits. We quantify the temperature dependence as well. Finally, we evaluate the s-wave scattering length and binding of the single van der Waals bound state of HeLi. We predict that this weakly bound level has a binding energy of -0.0064(43) x hc cm(-1) and -0.0122(67) x hc cm(-1) for He-4 + Li-6 and He-4 + Li-7, respectively. The calculated binding energy of He-4 + Li-7 is consistent with the sole experimental determination.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.101.012702}, author = {Makrides, Constantinos and Barker, Daniel S. and Fedchak, James A. and Scherschligt, Julia and Eckel, Stephen and Tiesinga, Eite} } @article { ISI:000507490800005, title = {Combining experiments and relativistic theory for establishing accurate radiative quantities in atoms: The lifetime of the P-2(3/2) state in Ca-40(+)}, journal = {Phys. Rev. A}, volume = {101}, number = {1}, year = {2020}, month = {JAN 14}, pages = {012509}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We report a precise determination of the lifetime of the (4p) P-2(3/2) state of Ca-40(+), tau(p3/2) = 6.639(42) ns, using a combination of measurements of the induced light shift and scattering rate on a single trapped ion. Good agreement with the result of a recent high-level theoretical calculation, 6.69(6) ns {[}M. S. Safronova et al., Phys. A 83, 012503 (2011)], but a 6-sigma discrepancy with the most precise previous experimental value, 6.924(19) ns {[}J. Jin et al., Phys. Rev. Lett. 70, 3213 (1993)], is found. To corroborate the consistency and accuracy of the new measurements, relativistically corrected ratios of reduced-dipole-matrix elements are used to directly compare our result with a recent result for the P-1/2 state, yielding a good agreement. The application of the present method to precise determinations of radiative quantities of molecular systems is discussed.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.101.012509}, author = {Meir, Ziv and Sinhal, Mudit and Safronova, Marianna S. and Willitsch, Stefan} } @article {oe_comparison_2020, title = {Comparison {Between} {NIST} {Graphene} and {AIST} {GaAs} {Quantized} {Hall} {Devices}}, journal = {IEEE Trans. Instrum. Meas.}, volume = {69}, number = {6, 1}, year = {2020}, note = {Place: 445 HOES LANE, PISCATAWAY, NJ 08855-4141 USA Publisher: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC Type: Article}, month = {jun}, pages = {3103{\textendash}3108}, abstract = {Several graphene quantized Hall resistance (QHR) devices manufactured at the National Institute of Standards and Technology (NIST) were compared with GaAs QHR devices and a 100-Omega standard resistor at the National Institute for Advanced Industrial Science and Technology (AIST). Measurements of a 100-Omega resistor with graphene QHR devices agreed within 5 n Omega/Omega of the values for a 100-Omega resistor obtained through GaAs measurements. The electron density of the graphene devices was adjusted at AIST to restore device properties such that operation was possible at low magnetic flux densities of 4-6 T. This adjustment was accomplished by a functionalization method utilized at NIST, allowing for consistent tunability of the graphene QHR devices with simple annealing. Such a method replaces older and less predictable methods for adjusting graphene for metrological suitability. The milestone results demonstrate the ease with which graphene can be used to make resistance comparison measurements among many National Metrology Institutes (NMIs).

}, keywords = {cryogenic current comparator, electron density, Epitaxial graphene (EG), quantized Hall resistance (QHR), standard resistor}, issn = {0018-9456}, doi = {10.1109/TIM.2019.2930436}, author = {Oe, Takehiko and Rigosi, Albert F. and Kruskopf, Mattias and Wu, Bi-Yi and Lee, Hsin-Yen and Yang, Yanfei and Elmquist, Randolph E. and Kaneko, Nobu-hisa and Jarrett, Dean G.} } @article { ISI:000571724100001, title = {A comparison of g((1)) (tau), g((3/2))(tau), and g((2))(tau) for radiation from harmonic oscillators in Brownian motion with a coherent background}, journal = {Phys. Scr.}, volume = {95}, number = {10}, year = {2020}, month = {OCT}, pages = {104001}, publisher = {IOP PUBLISHING LTD}, type = {Article}, abstract = {We compare the field-fieldg((1))(tau), intensity-fieldg((3/2))(tau), and intensity-intensityg((2))(tau) correlation functions for models that are of relevance in astrophysics. We obtain expressions for the general case of a chaotic radiation, where the amplitude is Rician based on a model with an ensemble of harmonic oscillators in Brownian motion. We obtain the signal to noise ratios for two methods of measurement. The intensity-field correlation function signal to noise ratio scales with the first power of vertical bar g((1))(tau). This is in contrast with the well-established result of g((2))(t)((2))(tau) which goes as the square of vertical bar g((1))(tau)vertical bar.}, keywords = {astrophysics, field correlation, intensity correlation, intensity-field correlation, Statistical Physics}, issn = {0031-8949}, doi = {10.1088/1402-4896/abac37}, author = {Siciak, A. and Hugbart, M. and Guerin, W. and Kaiser, R. and Orozco, L. A.} } @article {wu_competing_2020, title = {Competing quantum phases of hard-core bosons with tilted dipole-dipole interaction}, journal = {Phys. Rev. A}, volume = {102}, number = {5}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {nov}, abstract = {Different quantum phases of a hard-core boson induced by dipole-dipole interaction with varying angles of polarization are discussed in this work. We consider the two most influential leading terms with anisotropy due to the tilted polarization of the on-site boson in the square lattice. To ensure the concreteness of this truncation, we compare our phase diagrams, obtained numerically from the cluster mean-field theory (CMFT) and infinite projected entangled-pair state (iPEPS), with that of the long-range interacting model from quantum Monte Carlo. Next, we focus on the case where the azimuthal angle is fixed to phi = pi/4. Using the mean-field analysis where the quantum spin operators are replaced by c numbers, we aim to search for the underlying phases, especially the supersolid. Our results show a competing scenario mainly between two ordered phases with different sizes of unit cell, where a first-order transition takes place in between them. With the help of the CMFT and variational iPEPS, the phase boundaries predicted by the mean-field theory are determined more precisely. Our discoveries elucidate the possible underlying supersolid phases which might be seen in the ultracold experiments with strongly dipolar atoms. Moreover, our results indicate that an effective triangular optical lattice can be realized by fine tuning the polarization of dipoles in a square lattice.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.102.053306}, author = {Wu, Huan-Kuang and Tu, Wei-Lin} } @article { ISI:000530754200007, title = {Competition between factors determining bright versus dark atomic states within a laser mode}, journal = {Phys. Rev. A}, volume = {101}, number = {5}, year = {2020}, month = {MAY 7}, pages = {053410}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We observe bimodal fluorescence patterns from atoms in a fast atomic beam when the laser excitation occurs in the presence of a magnetic field and the atoms sample only a portion of the laser profile. The behavior is well explained by competition between the local intensity of the laser, which tends to generate a coherent-population-trapping (CPT) dark state in the J =1 to J{\textquoteright} = 0 system, and the strength of an applied magnetic field that can frustrate the CPT process. This work is relevant for understanding and optimizing the detection process for clocks or other coherent systems utilizing these transitions and could be applicable to in situ calibration of the laser-atom interaction, such as the strength of the magnetic field or laser intensity at a specific location.

}, issn = {2469-9926}, doi = {10.1103/PhysRevA.101.053410}, author = {Hemingway, Bryan and Akin, T. G. and Peil, Steven and Porto, J V} } @article { ISI:000581926500001, title = {Confinement of an alkaline-earth element in a grating magneto-optical trap}, journal = {Rev. Sci. Instrum.}, volume = {91}, number = {10}, year = {2020}, month = {OCT 1}, pages = {103202}, publisher = {AMER INST PHYSICS}, type = {Article}, abstract = {We demonstrate a compact magneto-optical trap (MOT) of alkaline-earth atoms using a nanofabricated diffraction grating chip. A single input laser beam, resonant with the broad S-1(0) -> P-1(1) transition of strontium, forms the MOT in combination with three diffracted beams from the grating chip and a magnetic field produced by permanent magnets. A differential pumping tube limits the effect of the heated, effusive source on the background pressure in the trapping region. The system has a total volume of around 2.4 l. With our setup, we have trapped up to 5 x 10(6) Sr-88 atoms at a temperature of similar to 6 mK, and with a trap lifetime of similar to 1 s. Our results will aid the effort to miniaturize quantum technologies based on alkaline-earth atoms.}, issn = {0034-6748}, doi = {10.1063/5.0019551}, author = {Sitaram, A. and Elgee, P. K. and Campbell, G. K. and Klimov, N. N. and Eckel, S. and Barker, D. S.} } @article { ISI:000506811300021, title = {Counting on Majorana modes}, journal = {Science}, volume = {367}, number = {6474}, year = {2020}, month = {JAN 10}, pages = {145}, publisher = {AMER ASSOC ADVANCEMENT SCIENCE}, type = {Article}, issn = {0036-8075}, doi = {10.1126/science.aaz9589}, author = {Sau, Jay} } @article { ISI:000532064500001, title = {Counting statistics of microwave photons in circuit QED}, journal = {Phys. Rev. A}, volume = {101}, number = {5}, year = {2020}, month = {MAY 13}, pages = {052321}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {In superconducting circuit architectures for quantum computing, microwave resonators are often used both to isolate qubits from the electromagnetic environment and to facilitate qubit state readout. We analyze the full counting statistics of photons emitted from such driven readout resonators both in and beyond the dispersive approximation. We calculate the overlap between emitted-photon distributions for the two qubit states and explore strategies for its minimization with the purpose of increasing fidelity of intensity-sensitive readout techniques. In the dispersive approximation and at negligible qubit relaxation, both distributions are Poissonian, and the overlap between them can be easily made arbitrarily small. Nondispersive terms of the Hamiltonian generate squeezing and the Purcell decay with the latter effect giving the dominant contribution to the overlap between two distributions.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.101.052321}, author = {Nesterov, Konstantin N. and Pechenezhskiy, V, Ivan and Vavilov, Maxim G.} } @article { ISI:000534162700004, title = {Creating solitons with controllable and near-zero velocity in Bose-Einstein condensates}, journal = {Phys. Rev. A}, volume = {101}, number = {5}, year = {2020}, month = {MAY 20}, pages = {053629}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Established techniques for deterministically creating dark solitons in repulsively interacting atomic Bose-Einstein condensates (BECs) can only access a narrow range of soliton velocities. Because velocity affects the stability of individual solitons and the properties of soliton-soliton interactions, this technical limitation has hindered experimental progress. Here we create dark solitons in highly anisotropic cigar-shaped BECs with arbitrary position and velocity by simultaneously engineering the amplitude and phase of the condensate wave function, improving upon previous techniques which explicitly manipulated only the condensate phase. The single dark soliton solution present in true one-dimensional (1D) systems corresponds to the kink soliton in anisotropic three-dimensional systems and is joined by a host of additional dark solitons, including vortex ring and solitonic vortex solutions. We readily create dark solitons with speeds from zero to half the sound speed. The observed soliton oscillation frequency suggests that we imprinted solitonic vortices, which for our cigar-shaped system are the only stable solitons expected for these velocities. Our numerical simulations of 1D BECs show this technique to be equally effective for creating kink solitons when they are stable. We demonstrate the utility of this technique by deterministically colliding dark solitons with domain walls in two-component spinor BECs.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.101.053629}, author = {Fritsch, A. R. and Lu, Mingwu and Reid, G. H. and Pineiro, A. M. and Spielman, I. B.} } @article { ISI:000510386300003, title = {Critical local moment fluctuations and enhanced pairing correlations in a cluster Anderson model}, journal = {Phys. Rev. B}, volume = {101}, number = {1}, year = {2020}, month = {JAN 31}, pages = {014452}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The appearance of unconventional superconductivity near heavy-fermion quantum critical points (QCPs) motivates investigation of pairing correlations close to a {\textquoteleft}{\textquoteleft}beyond Landau{{\textquoteright}{\textquoteright}} Kondo-destruction QCP. We focus on a two-Anderson-impurity cluster in which Kondo destruction is induced by a pseudogap in the conduction-electron density of states. Analysis via continuous-time quantum Monte Carlo and the numerical renormalization group reveals a previously unstudied QCP that both displays the critical-local moment fluctuations characteristic of Kondo destruction and leads to a strongly enhanced singlet-pairing susceptibility. Our results provide insights into the mechanism for superconductivity in quantum critical metals.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.101.014452}, author = {Cai, Ang and Pixley, J. H. and Ingersent, Kevin and Si, Qimiao} } @article {liang_cryspnet_2020, title = {{CRYSPNet}: {Crystal} structure predictions via neural networks}, journal = {Phys. Rev. Mater.}, volume = {4}, number = {12}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {dec}, abstract = {Structure is the most basic and important property of crystalline solids; it determines directly or indirectly most materials characteristics. However, predicting crystal structure of solids remains a formidable and not fully solved problem. Standard theoretical tools for this task are computationally expensive and at times inaccurate. Here we present an alternative approach utilizing machine learning for crystal structure prediction. We developed a tool called Crystal Structure Prediction Network (CRYSPNet) that can predict the Bravais lattice, space group, and lattice parameters of an inorganic material based only on its chemical composition. CRYSPNet consists of a series of neural network models, using as inputs predictors aggregating the properties of the elements constituting the compound. It was trained and validated on more than 100 000 entries from the Inorganic Crystal Structure Database. The tool demonstrates robust predictive capability and outperforms alternative strategies by a large margin. It can be used both as an independent prediction engine and as a method to generate candidate structures for further computational and/or experimental validation.

}, issn = {2475-9953}, doi = {10.1103/PhysRevMaterials.4.123802}, author = {Liang, Haotong and Stanev, Valentin and Kusne, A. Gilad and Takeuchi, Ichiro} } @article {colussi_cumulant_2020, title = {Cumulant theory of the unitary {Bose} gas: {Prethermal} and {Efimovian} dynamics}, journal = {Phys. Rev. A}, volume = {102}, number = {6}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {dec}, abstract = {We study the quench of a degenerate ultracold Bose gas to the unitary regime, where interactions are as strong as allowed by quantum mechanics. We lay the foundation of a cumulant theory able to simultaneously capture the three-body Efimov effect and ergodic evolution. After an initial period of rapid quantum depletion, a universal prethermal stage is established, characterized by a kinetic temperature and an emergent Bogoliubov dispersion law, while the microscopic degrees of freedom remain far from equilibrium. Integrability is then broken by higher-order interaction terms in the many-body Hamiltonian, leading to a momentum-dependent departure from power law to decaying exponential behavior of the occupation numbers at large momentum. We also find signatures of the Efimov effect in the many-body dynamics and make a precise identification between the observed beating phenomenon and the binding energy of an Efimov trimer. Throughout the paper, our predictions for a uniform gas are quantitatively compared with experimental results for quenched unitary Bose gases in uniform potentials.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.102.063314}, author = {Colussi, V. E. and Kurkjian, H. and Van Regemortel, M. and Musolino, S. and van de Kraats, J. and Wouters, M. and Kokkelmans, S. J. J. M. F.} } @article {tran_destructive_2020, title = {Destructive {Error} {Interference} in {Product}-{Formula} {Lattice} {Simulation}, journal = {Phys. Rev. Lett.}, volume = {124}, number = {22}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {jun}, abstract = {Quantum computers can efficiently simulate the dynamics of quantum systems. In this Letter, we study the cost of digitally simulating the dynamics of several physically relevant systems using the first-order product-formula algorithm. We show that the errors from different Trotterization steps in the algorithm can interfere destructively, yielding a much smaller error than previously estimated. In particular, we prove that the total error in simulating a nearest-neighbor interacting system of n sites for time t using the first-order product formula with r time slices is O(nt/r + nt(3)/r(2)) when nt(2)/r is less than a small constant. Given an error tolerance epsilon, the error bound yields an estimate of max\{O(n(2)t/epsilon), O(n(2)t(3/2)/epsilon(1/2))\} for the total gate count of the simulation. The estimate is tighter than previous bounds and matches the empirical performance observed in Childs et al. [Proc. Natl. Acad. Sci. U.S.A. 115, 9456 (2018)]. We also provide numerical evidence for potential improvements and conjecture an even tighter estimate for the gate count.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.124.220502}, author = {Tran, Minh C. and Chu, Su-Kuan and Su, Yuan and Childs, Andrew M. and Gorshkov, V, Alexey} } @article { ISI:000569266900003, title = {Detecting Acoustic Blackbody Radiation with an Optomechanical Antenna}, journal = {Phys. Rev. Lett.}, volume = {125}, number = {12}, year = {2020}, month = {SEP 15}, pages = {120603}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Nanomechanical systems are generally embedded in a macroscopic environment where the sources of thermal noise are difficult to pinpoint. We engineer a silicon nitride membrane optomechanical resonator such that its thermal noise is acoustically driven by a spatially well-defined remote macroscopic bath. This bath acts as an acoustic blackbody emitting and absorbing acoustic radiation through the silicon substrate. Our optomechanical system acts as a sensitive detector for the blackbody temperature and for photoacoustic imaging. We demonstrate that the nanomechanical mode temperature is governed by the blackbody temperature and not by the local material temperature of the resonator. Our work presents a route to mitigate self-heating effects in optomechanical thermometry and other quantum optomechanics experiments, as well as acoustic communication in quantum information.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.125.120603}, author = {Singh, Robinjeet and Purdy, Thomas P.} } @article { ISI:000557736300003, title = {Detection of the Lowest-Lying Odd-Parity Atomic Levels in Actinium}, journal = {Phys. Rev. Lett.}, volume = {125}, number = {7}, year = {2020}, month = {AUG 10}, pages = {073001}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Two lowest-energy odd-parity atomic levels of actinium, 7s(2)7p(2)P(1/2)(0), 7s(2)7p(2)P(3/)(2)(0), were observed via two-step resonant laser-ionization spectroscopy and their respective energies were measured to be 7477.36(4) and 12 276.59(2) cm(-1). The lifetimes of these states were determined as 668(11) and 255(7) ns, respectively. In addition, we observed the effect of the hyperfine structure on the line for the transition to P-2(3)/2(0). These properties were calculated using a hybrid approach that combines configuration interaction and coupled-cluster methods, in good agreement with the experiment. The data are of relevance for understanding the complex atomic spectra of actinides and for developing efficient laser cooling and ionization schemes for actinium, with possible applications for high-purity medical-isotope production and future fundamental physics experiments.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.125.073001}, author = {Zhang, Ke and Studer, Dominik and Weber, Felix and Gadelshin, Vadim M. and Kneip, Nina and Raeder, Sebastian and Budker, Dmitry and Wendt, Klaus and Kieck, Tom and Porsev, Sergey G. and Cheung, Charles and Safronova, Marianna S. and Kozlov, Mikhail G.} } @article { ISI:000541833200001, title = {Development of gateless quantum Hall checkerboardp-njunction devices}, journal = {J. Phys. D-Appl. Phys.}, volume = {53}, number = {34}, year = {2020}, month = {AUG 19}, pages = {345302}, publisher = {IOP PUBLISHING LTD}, type = {Article}, abstract = {Measurements of fractional multiples of the nu=2 plateau quantized Hall resistance (R-H approximate to 12 906 omega) were enabled by the utilization of multiple current terminals on millimetre-scale graphenep-njunction (pnJ) devices fabricated with interfaces along both lateral directions. These quantum Hall resistance checkerboard devices have been demonstrated to match quantized resistance outputs numerically calculated with the LTspice circuit simulator. From the devices{\textquoteright} functionality, more complex embodiments of the quantum Hall resistance checkerboard were simulated to highlight the parameter space within which these devices could operate. Moreover, these measurements suggest that the scalability ofpnJ fabrication on millimetre or centimetre scales is feasible with regards to graphene device manufacturing by using the far more efficient process of standard ultraviolet lithography.}, keywords = {epitaxial graphene, LTspice circuit simulator, p-njunctions, quantum Hall effect}, issn = {0022-3727}, doi = {10.1088/1361-6463/ab8d6f}, author = {Patel, Dinesh K. and Marzano, Martina and Liu, I, Chieh- and Kruskopf, Mattias and Elmquist, Randolph E. and Liang, Chi-Te and Rigosi, Albert F.} } @inbook {else_discrete_2020, title = {Discrete {Time} {Crystals}}, booktitle = {Annual Review of Condensed Matter Physics}, series = {Annual {Review} of {Condensed} {Matter} {Physics}}, volume = {11}, year = {2020}, note = {ISSN: 1947-5454 Journal Abbreviation: Annu. Rev. Condens. Matter Phys. Type: Review; Book Chapter}, pages = {467{\textendash}499}, publisher = {ANNUAL REVIEWS}, organization = {ANNUAL REVIEWS}, abstract = {Experimental advances have allowed for the exploration of nearly isolated quantum many-body systems whose coupling to an external bath is very weak. A particularly interesting class of such systems is those that do not thermalize under their own isolated quantum dynamics. In this review, we highlight the possibility for such systems to exhibit new nonequilibrium phases of matter. In particular, we focus on discrete time crystals, which are many-body phases of matter characterized by a spontaneously broken discrete time-translation symmetry. We give a definition of discrete time crystals from several points of view, emphasizing that they are a nonequilibrium phenomenon that is stabilized by many-body interactions, with no analog in noninteracting systems. We explain the theory behind several proposed models of discrete time crystals, and compare several recent realizations, in different experimental contexts.

}, keywords = {Floquet systems, isolated quantum many-body systems, many-body localization, spontaneous symmetry breaking, time-translation symmetry}, doi = {10.1146/annurev-conmatphys-031119-050658}, author = {Else, Dominic V. and Monroe, Christopher and Nayak, Chetan and Yao, Norman Y.}, editor = {Marchetti, MC and Mackenzie, AP} } @article {wilson_disorder_2020, title = {Disorder in twisted bilayer graphene}, journal = {Phys. Rev. Res.}, volume = {2}, number = {2}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {jun}, abstract = {We develop a theory for a type of disorder in condensed matter systems arising from local twist-angle fluctuations in two strongly coupled van der Waals monolayers twisted with respect to each other to create a flat-band moire superlattice. The paradigm of {\textquotedblleft}twist-angle disorder{\textquotedblright} arises from the currently ongoing intense research activity in the physics of twisted bilayer graphene. In experimental samples of pristine twisted bilayer graphene, which are nominally free of impurities and defects, the main source of disorder is believed to arise from the unavoidable and uncontrollable nonuniformity of the twist angle across the sample. To address this physics of twist-angle disorder, we develop a real-space, microscopic model of twisted bilayer graphene where the angle enters as a free parameter. In particular, we focus on the size of single-particle energy gaps separating the miniband from the rest of the spectrum, the Van Hove peaks, the renormalized Dirac cone velocity near charge neutrality, and the minibandwidth. We find that the energy gaps and minibandwidth are strongly affected by disorder while the renormalized velocity remains virtually unchanged. We discuss the implications of our results for the ongoing experiments on twisted bilayer graphene. Our theory is readily generalized to future studies of twist-angle disorder effects on all electronic properties of moire superlattices created by twisting two coupled van der Waals materials with respect to each other.}, doi = {10.1103/PhysRevResearch.2.023325}, author = {Wilson, Justin H. and Fu, Yixing and Das Sarma, S. and Pixley, J. H.} } @article { ISI:000541476900001, title = {Dissipative Kerr Solitons in a III-V Microresonator}, journal = {Laser Photon. Rev.}, volume = {14}, number = {8}, year = {2020}, month = {AUG}, pages = {2000022}, publisher = {WILEY-V C H VERLAG GMBH}, type = {Article}, abstract = {Stable microresonator Kerr soliton frequency combs in a III-V platform (AlGaAs on SiO2) are demonstrated through quenching of thermorefractive effects by cryogenic cooling to temperatures between 4 and 20 K. This cooling reduces the resonator{\textquoteright}s thermorefractive coefficient, whose room-temperature value is an order of magnitude larger than that of other microcomb platforms like Si3N4, SiO2, and AlN, by more than two orders of magnitude, and makes soliton states adiabatically accessible. Realizing such phase-stable soliton operation is critical for applications that fully exploit the ultra-high effective nonlinearity and high optical quality factors exhibited by this platform.}, keywords = {frequency combs, GaAs, microcombs, nanophotonics, Nonlinear optics, soliton}, issn = {1863-8880}, doi = {10.1002/lpor.202000022},}, author = {Moille, Gregory and Chang, Lin and Xie, Weiqiang and Rao, Ashutosh and Lu, Xiyuan and Davanco, Marcelo and Bowers, John E. and Srinivasan, Kartik} } @article { ISI:000530026700003, title = {Drag viscosity of metals and its connection to Coulomb drag}, journal = {Phys. Rev. B}, volume = {101}, number = {19}, year = {2020}, month = {MAY 4}, pages = {195106}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Recent years have seen a surge of interest in studies of hydrodynamic transport in electronic systems. We investigate the electron viscosity of metals and find a component that is closely related to Coulomb drag. By using linear-response theory, viscosity, which is a transport coefficient for momentum, can be extracted from the retarded correlation function of the momentum flux, i.e., the stress tensor. There exists a previously overlooked contribution to the shear viscosity from the interacting part of the stress tensor which accounts for the momentum flow induced by interactions. This contribution, which we dub drag viscosity, is caused by the frictional drag force due to long-range interactions. It is therefore linked to Coulomb drag which also originates from the interaction-induced drag force. Starting from the Kubo formula and using the Keldysh technique, we compute the drag viscosity of two- and three-dimensional metals along with the drag resistivity of double-layer two-dimensional electronic systems. Both the drag resistivity and drag viscosity exhibit a crossover from quadraticin-T behavior at low temperatures to a linear behavior at higher temperatures. Although the drag viscosity appears relatively small compared with the normal Drude component for the clean metals, it may dominate hydrodynamic transport in some systems, which are discussed in the conclusion.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.101.195106}, author = {Liao, Yunxiang and Galitski, Victor} } @article { ISI:000530023600007, title = {d-wave superconductivity and Bogoliubov-Fermi surfaces in Rarita-Schwinger-Weyl semimetals}, journal = {Phys. Rev. B}, volume = {101}, number = {18}, year = {2020}, month = {MAY 4}, pages = {184503}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We uncover the properties of complex tensor (d-wave) superconducting order in three-dimensional Rarita-Schwinger-Weyl semimetals that host pseudospin-3/2 fermions at a fourfold linear band-crossing point. Although the general theory of d-wave order was originally developed for materials displaying quadratic band touching, it directly applies to the case of semimetals with linear dispersion, several candidate compounds of which have been discovered experimentally very recently. The spin-3/2 nature of the fermions allows for the formation of spin-2 Cooper pairs which may be described by a complex second-rank tensor order parameter. In the case of linear dispersion, for the chemical potential at the Fermi point and at strong coupling, the energetically preferred superconducting state is the uniaxial nematic state, which preserves time-reversal symmetry and provides a full (anisotropic) gap for quasiparticle excitations. In contrast, at a finite chemical potential, we find that the usual weak-coupling instability is toward the {\textquoteleft}{\textquoteleft}cyclic state,{{\textquoteright}{\textquoteright}} well known from the studies of multicomponent Bose-Einstein condensates, which breaks time-reversal symmetry maximally, has vanishing average value of angular momentum, and features 16 small Bogoliubov-Fermi surfaces. The Rarita-Schwinger-Weyl semimetals provide therefore the first example of weakly coupled, three-dimensional, isotropic d-wave superconductors where the d-wave superconducting phase is uniquely selected by the quartic expansion of the mean-field free energy, and is not afflicted by the accidental degeneracy first noticed by Mermin over 40 years ago. We discuss the appearance and stability of the Bogoliubov-Fermi surfaces in absence of inversion symmetry in the electronic Hamiltonian, as in the case at hand.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.101.184503}, author = {Link, Julia M. and Boettcher, Igor and Herbut, Igor F.} } @article {tran_dynamical_2020, title = {Dynamical {Josephson} effects in {NbSe2}, journal = {Phys. Rev. Res.}, volume = {2}, number = {4}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {nov}, abstract = {The study of superconducting materials that also possess nontrivial correlations or interactions remains an active frontier of condensed matter physics. NbSe2 belongs to this class of superconductors and recent research has focused on the two-dimensional properties of this layered, superconducting material. Often, electronic transport measurements are used to investigate the superconducting properties of these materials, hence it is key to obtain a thorough understanding of transport in these systems. We investigate the transition between the superconducting and resistive state using radio-frequency AC excitation. Despite being a single piece of superconductor, the devices show novel dynamical Josephson effects behavior reminiscent of the AC Josephson effect observed in Josephson junctions. Detailed analysis uncovers the origin of this effect, identifying two types of vortex motion that categorize the transition to the normal state. Our results shed light on the nature of superconductivity in this material, unearthing exotic phenomena by exploiting nonequilibrium superconducting effects in atomically thin materials.}, doi = {10.1103/PhysRevResearch.2.043204}, author = {Tran, S. and Sell, J. and Williams, J. R.} } @article { ISI:000544526900013, title = {Early-Time Exponential Instabilities in Nonchaotic Quantum Systems}, journal = {Phys. Rev. Lett.}, volume = {125}, number = {1}, year = {2020}, month = {JUL 1}, pages = {014101}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The majority of classical dynamical systems are chaotic and exhibit the butterfly effect: a minute change in initial conditions has exponentially large effects later on. But this phenomenon is difficult to reconcile with quantum mechanics. One of the main goals in the field of quantum chaos is to establish a correspondence between the dynamics of classical chaotic systems and their quantum counterparts. In isolated systems in the absence of decoherence, there is such a correspondence in dynamics, but it usually persists only over a short time window, after which quantum interference washes out classical chaos. We demonstrate that quantum mechanics can also play the opposite role and generate exponential instabilities in classically nonchaotic systems within this early-time window. Our calculations employ the out-of-time-ordered correlator (OTOC)-a diagnostic that reduces to the Lyapunov exponent in the classical limit but is well defined for general quantum systems. We show that certain classically nonchaotic models, such as polygonal billiards, demonstrate a Lyapunov-like exponential growth of the OTOC at early times with Planck{\textquoteright}s-constant-dependent rates. This behavior is sharply contrasted with the slow early-time growth of the analog of the OTOC in the systems{\textquoteright} classical counterparts. These results suggest that classical-to-quantum correspondence in dynamics is violated in the OTOC even before quantum interference develops.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.125.014101}, author = {Rozenbaume, Efim B. and Bunimovich, Leonid A. and Galitski, Victor} } @article { ISI:000509352500053, title = {Effect of imperfect homodyne visibility on multi-spatial-mode two-mode squeezing measurements}, journal = {Opt. Express}, volume = {28}, number = {1}, year = {2020}, month = {JAN 6}, pages = {652-664}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {We study the effect of homodyne detector visibility on the measurement of quadrature squeezing for a spatially multi-mode source of two-mode squeezed light. Sources like optical parametric oscillators (OPO) typically produce squeezing in a single spatial mode because the nonlinear medium is within a mode-selective optical cavity. For such a source, imperfect interference visibility in the homodyne detector couples in additional vacuum noise, which can be accounted for by introducing an equivalent loss term. In a free-space multi-spatial-mode system imperfect homodyne detector visibility can couple in uncorrelated squeezed modes, and hence can cause faster degradation of the measured squeezing. We show experimentally the dependence of the measured squeezing level on the visibility of homodyne detectors used to probe two-mode squeezed states produced by a free space tour-wave mixing process in Rb-85 vapor, and also demonstrate that a simple theoretical model agrees closely with the experimental data. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement}, issn = {1094-4087}, doi = {10.1364/OE.379033}, author = {Gupta, Prasoon and Speirs, Rory W. and Jones, Kevin M. and Lett, Paul D.} } @article { ISI:000552791500001, title = {The effect of strain on tunnel barrier height in silicon quantum devices}, journal = {J. Appl. Phys.}, volume = {128}, number = {2}, year = {2020}, month = {JUL 14}, pages = {024303}, publisher = {AMER INST PHYSICS}, type = {Article}, abstract = {Semiconductor quantum dot (QD) devices experience a modulation of the band structure at the edge of lithographically defined gates due to mechanical strain. This modulation can play a prominent role in the device behavior at low temperatures, where QD devices operate. Here, we develop an electrical measurement of strain based on I ( V ) characteristics of tunnel junctions defined by aluminum and titanium gates. We measure relative differences in the tunnel barrier height due to strain consistent with experimentally measured coefficients of thermal expansion ( alpha) that differ from the bulk values. Our results show that the bulk parameters commonly used for simulating strain in QD devices incorrectly capture the impact of strain. The method presented here provides a path forward toward exploring different gate materials and fabrication processes in silicon QDs in order to optimize strain.}, issn = {0021-8979}, doi = {10.1063/5.0010253}, author = {Stein, Ryan M. and Stewart, Jr., M. D.} } @article {bringewatt_effective_2020, title = {Effective {Gaps} {Are} {Not} {Effective}: {Quasipolynomial} {Classical} {Simulation} of {Obstructed} {Stoquastic} {Hamiltonians}}, journal = {Phys. Rev. Lett.}, volume = {125}, number = {17}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {oct}, abstract = {All known examples suggesting an exponential separation between classical simulation algorithms and stoquastic adiabatic quantum computing (StoqAQC) exploit symmetries that constrain adiabatic dynamics to effective, symmetric subspaces. The symmetries produce large effective eigenvalue gaps, which in turn make adiabatic computation efficient. We present a classical algorithm to subexponentially sample from an effective subspace of any k-local stoquastic Hamiltonian H, without a priori knowledge of its symmetries (or near symmetries). Our algorithm maps any k-local Hamiltonian to a graph G = (V, E) with vertical bar V vertical bar = O(poly(n)), where n is the number of qubits. Given the well-known result of Babai [Graph isomorphism in quasipolynomial time, in Proceedings of the Forty-Eighth Annual ACM Symposium on Theory of Computing (2016), pp. 684-697], we exploit graph isomorphism to study the automorphisms of G and arrive at an algorithm quasipolynomial in vertical bar V vertical bar for producing samples from effective subspace eigenstates of H. Our results rule out exponential separations between StoqAQC and classical computation that arise from hidden symmetries in k-local Hamiltonians. Our graph representation of H is not limited to stoquastic Hamiltonians and may rule out corresponding obstructions in nonstoquastic cases, or be useful in studying additional properties of k-local Hamiltonians.

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.125.170504}, author = {Bringewatt, Jacob and Jarret, Michael} } @article { ISI:000568842200012, title = {Effects of conical intersections on hyperfine quenching of hydroxyl OH in collision with an ultracold Sr atom}, journal = {Sci Rep}, volume = {10}, number = {1}, year = {2020}, month = {AUG 24}, pages = {14130}, publisher = {NATURE PUBLISHING GROUP}, type = {Article}, abstract = {The effect of conical intersections (CIs) on electronic relaxation, transitions from excited states to ground states, is well studied, but their influence on hyperfine quenching in a reactant molecule is not known. Here, we report on ultracold collision dynamics of the hydroxyl free-radical OH with Sr atoms leading to quenching of OH hyperfine states. Our quantum-mechanical calculations of this process reveal that quenching is efficient due to anomalous molecular dynamics in the vicinity of the conical intersection at collinear geometry. We observe wide scattering resonance features in both elastic and inelastic rate coefficients at collision energies below k(B) x 10mK. They are identified as either p- or d-wave shape resonances. We also describe the electronic potentials relevant for these non-reactive collisions, their diabatization procedure, as well as the non-adiabatic coupling between the diabatic potentials near the CIs.}, issn = {2045-2322}, doi = {10.1038/s41598-020-71068-w}, author = {Li, Ming and Klos, Jacek and Petrov, Alexander and Li, Hui and Kotochigova, Svetlana} } @article { ISI:000553250400007, title = {Efficient Ground-State Cooling of Large Trapped-Ion Chains with an Electromagnetically-Induced-Transparency Tripod Scheme}, journal = {Phys. Rev. Lett.}, volume = {125}, number = {5}, year = {2020}, month = {JUL 29}, pages = {053001}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We report the electromagnetically-induced-transparency (EIT) cooling of a large trapped Yb-171(+) ion chain to the quantum ground state. Unlike conventional EIT cooling, we engage a four-level tripod structure and achieve fast sub-Doppler cooling over all motional modes. We observe simultaneous groundstate cooling across the complete transverse mode spectrum of up to 40 ions, occupying a bandwidth of over 3 MHz. The cooling time is observed to be less than 300 mu s, independent of the number of ions. Such efficient cooling across the entire spectrum is essential for high-fidelity quantum operations using trapped ion crystals for quantum simulators or quantum computers.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.125.053001}, author = {Feng, L. and Tan, W. L. and De, A. and Menon, A. and Chu, A. and Pagano, G. and Monroe, C.} } @article {19016, title = {Efficient photoinduced second-harmonic generation in silicon nitride photonics}, journal = {Nature Photonics}, year = {2020}, month = {11/2020}, abstract = {Silicon photonics lacks a second-order nonlinear optical (Ï‡(2)) response in general, because the typical constituent materials are centrosymmetric and lack inversion symmetry, which prohibits Ï‡(2) nonlinear processes such as second-harmonic generation (SHG). Here, we realize high SHG efficiency in silicon photonics by combining a photoinduced effective Ï‡(2) nonlinearity with resonant enhancement and perfect phase matching. We show a conversion efficiency of (2,500\ {\textpm}\ 100)\%\ W-1 that is two to four orders of magnitude larger than previous field-induced SHG works. In particular, our devices realize milliwatt-level SHG output powers with up to (22\ {\textpm}\ 1)\% power conversion efficiency. This demonstration is a breakthrough in realizing efficient Ï‡(2) processes in silicon photonics, and paves the way for further integration of self-referenced frequency combs and optical frequency references.

}, issn = {1749-4893}, doi = {10.1038/s41566-020-00708-4}, url = {https://doi.org/10.1038/s41566-020-00708-4}, author = {Lu, Xiyuan and Moille, Gregory and Rao, Ashutosh and Westly, Daron A. and Srinivasan, Kartik} } @conference {lu_efficient_2020, title = {Efficient second harmonic generation in a {Si3N4} microring}, booktitle = {Conference on Lasers and Electro-Optics (CLEO)}, series = {Conference on {Lasers} and {Electro}-{Optics}}, year = {2020}, note = {Backup Publisher: IEEE ISSN: 2160-9020 Type: Proceedings Paper}, publisher = {IEEE}, organization = {IEEE}, abstract = {We demonstrate efficient second harmonic generation in a silicon nitride microring, through perfect phase matching of a photogalvanic DC-field-induced chi((2)) process. The efficiency of 2,500 \%/W is {\textgreater} 100 x larger than the previous record in silicon photonics. (c) 2020 The Author(s)

}, isbn = {978-1-943580-76-7}, author = {Lu, Xiyuan and Moille, Gregory and Rao, Ashutosh and Westly, Daron and Li, Qing and Srinivasan, Kartik} } @conference {lu_efficient_2020-1, title = {Efficient widely-separated optical parametric oscillation}, booktitle = {Conference on Lasers and Electro-Optics (CLEO)}, series = {Conference on {Lasers} and {Electro}-{Optics}}, year = {2020}, note = {Backup Publisher: IEEE ISSN: 2160-9020 Type: Proceedings Paper}, publisher = {IEEE}, organization = {IEEE}, abstract = {We demonstrate the first widely-separated optical parametric oscillation in silicon nanophotonics, with milliwatt-level threshold power that is {\textgreater} 50 times smaller than other widely-separated OPOs. This demonstration is promising for on-chip visible light generation. (C) 2020 The Author(s)

}, isbn = {978-1-943580-76-7}, author = {Lu, Xiyuan and Moille, Gregory and Singh, Anshuman and Li, Qing and Westly, Daron and Rao, Ashutosh and Yu, Su-Peng and Briles, Travis C. and Drake, Tara and Papp, Scott B. and Srinivasan, Kartik} } @article { ISI:000510841200002, title = {Electron-induced massive dynamics of magnetic domain walls}, journal = {Phys. Rev. B}, volume = {101}, number = {5}, year = {2020}, month = {FEB 4}, pages = {054407}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study the dynamics of domain walls (DWs) in a metallic, ferromagnetic nanowire, focusing on inertial effects on the DW due to interaction with a conduction electron bath. We develop a Keldysh collective coordinate technique to describe the effect of conduction electrons on rigid magnetic structures. The effective Lagrangian and Langevin equations of motion for a DW are derived microscopically, including the full response kernel which is nonlocal in time. The DW dynamics is described by two collective degrees of freedom: position and tilt angle. The coupled Langevin equations therefore involve two correlated noise sources, leading to a generalized fluctuation-dissipation theorem (FDT). The DW response kernel due to electrons contains two parts: one related to dissipation via FDT and another reactive part. We prove that the latter term leads to a mass for both degrees of freedom, even though the intrinsic bare mass is zero. The electron-induced mass is present even in a clean system without pinning or specifically engineered potentials. The resulting equations of motion contain rich dynamical solutions and point toward a way to control domain wall motion in metals via the electronic system properties. We discuss two observable consequences of the mass, hysteresis in the DW dynamics, and resonant response to ac current.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.101.054407}, author = {Hurst, Hilary M. and Galitski, Victor and Heikkila, Tero T.} } @article {das_sarma_electron-phonon_2020, title = {Electron-phonon and electron-electron interaction effects in twisted bilayer graphene}, journal = {Ann. Phys.}, volume = {417}, year = {2020}, note = {Place: 525 B ST, STE 1900, SAN DIEGO, CA 92101-4495 USA Publisher: ACADEMIC PRESS INC ELSEVIER SCIENCE Type: Article}, month = {jun}, abstract = {By comparing with recently available experimental data from several groups, we critically discuss the manifestation of continuum many body interaction effects in twisted bilayer graphene (tBLG) with small twist angles and low carrier densities, which arise naturally within the Dirac cone approximation for the non-interacting band structure. We provide two specific examples of such continuum many body theories: one involving electron-phonon interaction and one involving electron-electron interaction. In both cases, the experimental findings are only partially quantitatively consistent with rather clear-cut leading-order theoretical predictions based on well-established continuum many body theories. We provide a critical discussion, based mainly on the currently available tBLG experimental data, on possible future directions for understanding many body renormalization involving electron-phonon and electron-electron interactions in the system. One definitive conclusion based on the comparison between theory and experiment is that the leading order 1-loop perturbative renormalization group theory completely fails to account for the electron-electron interaction effects in the strong-coupling limit of flatband moire tBLG system near the magic twist angle even at low doping where the Dirac cone approximation should apply. By contrast, approximate nonperturbative theoretical results based on Borel-Pade resummation or 1/N expansion seem to work well compared with experiments, indicating rather small interaction corrections to Fermi velocity or carrier effective mass. For electron-phonon interactions, however, the leading-order continuum theory works well except when van Hove singularities in the density of states come into play. (C) 2020 Elsevier Inc. All rights reserved.}, issn = {0003-4916}, doi = {10.1016/j.aop.2020.168193}, author = {Das Sarma, Sankar and Wu, Fengcheng} } @article {mueller_energy-based_2020, title = {Energy-{Based} {Plasmonicity} {Index} to {Characterize} {Optical} {Resonances} in {Nanostructures}}, journal = {J. Phys. Chem. C}, volume = {124}, number = {44, SI}, year = {2020}, note = {Place: 1155 16TH ST, NW, WASHINGTON, DC 20036 USA Publisher: AMER CHEMICAL SOC Type: Article}, month = {nov}, pages = {24331{\textendash}24343}, abstract = {Resonances sustained by plasmonic nanoparticles provide extreme electric field confinement and enhancement into the deep subwavelength domain for a plethora of applications. Recent progress in nanofabrication made it even possible to tailor the properties of nanoparticles consisting of only a few hundred atoms. These nanoparticles support both single-particle-like resonances and collective plasmonic charge density oscillations. Prototypical systems sustaining both features are graphene nanoantennas. In pushing the frontier of nanoscience, traditional identification, and classification of such resonances is at stake again. We show that in such nanostructures, the concerted electron cloud oscillation in real space does not necessarily come along with collective dynamics of conduction band electrons in energy space. This unveils an urgent need for a discussion of how a plasmon in nanostructures should be defined. Here, we propose to define it relying on energy space dynamics. The unambiguous identification of the plasmonic nature of a resonance is crucial to find out whether desirable plasmon-assisted features, such as frequency conversion processes, can be expected from a resonance. We elaborate an energy-based figure of merit that classifies the nature of resonances in nanostructures, motivated by tight binding simulations with a toy model consisting of a linear chain of atoms. We apply afterward the proposed figure of merit to a doped hexagonal graphene nanoantenna, which is known to support plasmons in the near infrared and single-particle-like transitions in the visible.

}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.0c07964}, author = {Mueller, Marvin M. and Kosik, Miriam and Pelc, Marta and Bryant, Garnett W. and Ayuela, Andres and Rockstuhl, Carsten and Slowik, Karolina} } @article { ISI:000562629600008, title = {Engineering quantum Hall phases in a synthetic bilayer graphene system}, journal = {Phys. Rev. B}, volume = {102}, number = {8}, year = {2020}, month = {AUG 26}, pages = {085430}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Synthetic quantum Hall bilayer (SQHB), realized by optically driven monolayer graphene in the quantum Hall regime, provides a flexible platform for engineering quantum Hall phases as discussed in Ghazaryan et al. {[}Phys. Rev. Lett. 119, 247403 (2017)]. The coherent driving which couples two Landau levels mimics an effective tunneling between synthetic layers. The tunneling strength, the effective Zeeman coupling, and two-body interaction matrix elements are tunable by varying the driving frequency and the driving strength. Using infinite density matrix renormalization group techniques combined with exact diagonalization, we show that the system exhibits a non-Abelian bilayer Fibonacci phase at filling fraction nu = 2/3. Moreover, at integer filling nu = 1, the SQHB exhibits quantum Hall ferromagnetism. Using Hartree-Fock theory and exact diagonalization, we show that excitations of the quantum Hall ferromagnet are topological textures known as skyrmions.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.085430}, author = {Cian, Ze-Pei and Grass, Tobias and Vaezi, Abolhassan and Liu, Zhao and Hafezi, Mohammad} } @article { ISI:000573650200006, title = {Enhanced transport of spin-orbit-coupled Bose gases in disordered potentials}, journal = {Phys. Rev. A}, volume = {102}, number = {3}, year = {2020}, month = {SEP 17}, pages = {033325}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Anderson localization is a single-particle localization phenomena in disordered media that is accompanied by an absence of diffusion. Spin-orbit coupling (SOC) describes an interaction between a particle{\textquoteright}s spin and its momentum that directly affects its energy dispersion, for example, creating dispersion relations with gaps and multiple local minima We show theoretically that combining one-dimensional spin-orbit coupling with a transverse Zeeman field suppresses the effects of disorder, thereby increasing the localization length and conductivity. This increase results from a suppression of backscattering between states in the gap of the SOC dispersion relation. Here, we focus specifically on the interplay of disorder from an optical speckle potential and SOC generated by two-photon Raman processes in quasi-one-dimensional Bose-Einstein condensates. We first describe backscattering by using a Fermi golden rule approach, and then numerically confirm this picture by solving the time-dependent one-dimensional Gross-Pitaevskii equation for a weakly interacting Bose-Einstein condensate with SOC and disorder. We find that on the tens of millisecond timescale of typical cold atom experiments moving in harmonic traps, initial states with momentum in the zero-momentum SOC gap evolve with negligible backscattering, while without SOC these same states rapidly localize.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.102.033325}, author = {Yue, Y. and de Melo, C. A. R. Sa and Spielman, I. B.} } @article {eldredge_entanglement_2020, title = {Entanglement bounds on the performance of quantum computing architectures}, journal = {Phys. Rev. Res.}, volume = {2}, number = {3}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {aug}, abstract = {There are many possible architectures of qubit connectivity that designers of future quantum computers will need to choose between. However, the process of evaluating a particular connectivity graph{\textquoteright}s performance as a quantum architecture can be difficult. In this paper, we show that a quantity known as the isoperimetric number establishes a lower bound on the time required to create highly entangled states. This metric we propose counts resources based on the use of two-qubit unitary operations, while allowing for arbitrarily fast measurements and classical feedback. We use this metric to evaluate the hierarchical architecture proposed by A. Bapat et al. [Phys. Rev. A 98, 062328 (2018)] and find it to be a promising alternative to the conventional grid architecture. We also show that the lower bound that this metric places on the creation time of highly entangled states can be saturated with a constructive protocol, up to a factor logarithmic in the number of qubits.}, doi = {10.1103/PhysRevResearch.2.033316}, author = {Eldredge, Zachary and Zhou, Leo and Bapat, Aniruddha and Garrison, James R. and Deshpande, Abhinav and Chong, Frederic T. and Gorshkov, V, Alexey} } @article { ISI:000515058400001, title = {Exact boundary modes in an interacting quantum wire}, journal = {Phys. Rev. B}, volume = {101}, number = {8}, year = {2020}, month = {FEB 21}, pages = {085133}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The boundary modes of one-dimensional quantum systems can play host to a variety of remarkable phenomena. They can be used to describe the physics of impurities in higher-dimensional systems, such as the ubiquitous Kondo effect, or can support Majorana bound states, which play a crucial role in the realm of quantum computation. In this work we examine the boundary modes in an interacting quantum wire with a proximity-induced pairing term. We solve the system exactly using the Bethe ansatz and show that for certain boundary conditions the spectrum contains bound states localized about either edge. The model is shown to exhibit a first-order phase transition as a function of the interaction strength such that for attractive interactions the ground state has bound states at both ends of the wire, while for repulsive interactions they are absent. In addition we see that the bound-state energy lies within the gap for all values of the interaction strength but undergoes a sharp avoided level crossing for sufficiently strong interaction, thereby preventing its decay. This avoided crossing is shown to occur as a consequence of an exact self-duality which is present in the model.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.101.085133}, author = {Rylands, Colin} } @article { ISI:000562633900003, title = {Exotic Photonic Molecules via Lennard-Jones-like Potentials}, journal = {Phys. Rev. Lett.}, volume = {125}, number = {9}, year = {2020}, month = {AUG 26}, pages = {093601}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Ultracold systems offer an unprecedented level of control of interactions between atoms. An important challenge is to achieve a similar level of control of the interactions between photons. Towards this goal, we propose a realization of a novel Lennard-Jones-like potential between photons coupled to the Rydberg states via electromagnetically induced transparency (EIT). This potential is achieved by tuning Rydberg states to a Forster resonance with other Rydberg states. We consider few-body problems in 1D and 2D geometries and show the existence of self-bound clusters ({{\textquoteright}{\textquoteright}}molecules{{\textquoteright}{\textquoteright}}) of photons. We demonstrate that for a few-body problem, the multibody interactions have a significant impact on the geometry of the molecular ground state. This leads to phenomena without counterparts in conventional systems: For example, three photons in two dimensions preferentially arrange themselves in a line configuration rather than in an equilateral-triangle configuration. Our result opens a new avenue for studies of many-body phenomena with strongly interacting photons.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.125.093601}, author = {Bienias, Przemyslaw and Gullans, Michael J. and Kalinowski, Marcin and Craddock, Alexander N. and Ornelas-Huerta, Dalia P. and Rolston, S. L. and Porto, V, J. and Gorshkov, V, Alexey} } @article {jabir_experimental_2020, title = {Experimental demonstration of the near-quantum optimal receiver}, journal = {OSA Continuum}, volume = {3}, number = {12}, year = {2020}, note = {Place: 2010 MASSACHUSETTS AVE NW, WASHINGTON, DC 20036 USA Publisher: OPTICAL SOC AMER Type: Article}, month = {dec}, pages = {3324+}, abstract = {We implement the cyclic quantum receiver based on the theoretical proposal of Roy Bondurant and demonstrate experimentally below the shot-noise limit (SNL) discrimination of quadrature phase-shift keying signals (PSK). We also experimentally test the receiver generalized for longer communication alphabet lengths and coherent frequency shift keying (CFSK) encoding. Using off-the-shelf components, we obtain state discrimination error rates that are 3 dB and 4.6 dB below the SNLs of ideal classical receivers for quadrature PSK and CFSK encodings, respectively. The receiver unconditionally surpasses the SNL for M=8 PSK and CFSK. This receiver can be used for the simple and robust practical implementation of quantum-enhanced optical communication. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement}, issn = {2578-7519}, doi = {10.1364/OSAC.409200}, author = {Jabir, V, M. and Burenkov, I. A. and Annafianto, N. Fajar R. and Battou, A. and Polyakov, V, S.} } @article {winer_exponential_2020, title = {Exponential {Ramp} in the {Quadratic} {Sachdev}-{Ye}-{Kitaev} {Model}}, journal = {Phys. Rev. Lett.}, volume = {125}, number = {25}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {dec}, abstract = {A long period of linear growth in the spectral form factor provides a universal diagnostic of quantum chaos at intermediate times. By contrast, the behavior of the spectral form factor in disordered integrable many-body models is not well understood. Here we study the two-body Sachdev-Ye-Kitaev model and show that the spectral form factor features an exponential ramp, in sharp contrast to the linear ramp in chaotic models. We find a novel mechanism for this exponential ramp in terms of a high-dimensional manifold of saddle points in the path integral formulation of the spectral form factor. This manifold arises because the theory enjoys a large symmetry group. With finite nonintegrable interaction strength, these delicate symmetries reduce to a relative time translation, causing the exponential ramp to give way to a linear ramp.

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.125.250602}, author = {Winer, Michael and Jian, Shao-Kai and Swingle, Brian} } @article {yang_extended_2020, title = {Extended nonergodic regime and spin subdiffusion in disordered {SU}(2)-symmetric {Floquet} systems}, journal = {Phys. Rev. B}, volume = {102}, number = {21}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {dec}, abstract = {We explore thermalization and quantum dynamics in a one-dimensional disordered SU(2)-symmetric Floquet model, where a many-body localized phase is prohibited by the non-Abelian symmetry. Despite the absence of localization, we find an extended nonergodic regime at strong disorder where the system exhibits nonthermal behaviors. In the strong disorder regime, the level spacing statistics exhibit neither a Wigner-Dyson nor a Poisson distribution, and the spectral form factor does not show a linear-in-time growth at early times characteristic of random matrix theory. The average entanglement entropy of the Floquet eigenstates is subthermal, although violating an area-law scaling with system sizes. We further compute the expectation value of local observables and find strong deviations from the eigenstate thermalization hypothesis. The infinite-temperature spin autocorrelation function decays at long times as t(-beta) with beta {\textless} 0.5, indicating subdiffusive transport at strong disorders.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.214205}, author = {Yang, Zhi-Cheng and Nicholls, Stuart and Cheng, Meng} } @article { ISI:000526522000042, title = {Extreme ultraviolet photon conversion efficiency of tetraphenyl butadiene}, journal = {Appl. Optics}, volume = {59}, number = {4}, year = {2020}, month = {FEB 1}, pages = {1217-1224}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {Extreme ultraviolet (EUV) radiation can be converted to visible light using tetraphenyl butadiene (TPB) as a phosphor. 1 mu m films of TPB were prepared using thermal vapor deposition of the pure material and by spin coating suspensions of TPB in high-molecular-weight polystyrene/toluene solutions. Calibrated sources and detectors were used to determine the effective photon conversion efficiency of the films for incident EUV radiation in the wavelength range of 125 nm <= lambda <= 200 nm. After exposure to atmosphere, the efficiency of the vapor-deposited films decreased significantly, while the efficiency of the spin-coated films remained unchanged. The production of TPB films by spin coating offers the advantages of simplicity and long-term stability. (C) 2020 Optical Society of America}, issn = {1559-128X}, doi = {10.1364/AO.380185}, author = {Graybill, Joshua R. and Shahi, Chandra B. and Coplan, Michael A. and Thompson, Alan K. and Vest, Robert E. and Clark, Charles W.} } @article {hurst_feedback_2020, title = {Feedback induced magnetic phases in binary {Bose}-{Einstein} condensates}, journal = {Phys. Rev. Res.}, volume = {2}, number = {4}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {dec}, abstract = {Weak measurement in tandem with real-time feedback control is a new route toward engineering novel nonequilibrium quantum matter. Here we develop a theoretical toolbox for quantum feedback control of multicomponent Bose-Einstein condensates (BECs) using backaction-limited weak measurements in conjunction with spatially resolved feedback. Feedback in the form of a single-particle potential can introduce effective interactions that enter into the stochastic equation governing system dynamics. The effective interactions are tunable and can be made analogous to Feshbach resonances-spin independent and spin dependent-but without changing atomic scattering parameters. Feedback cooling prevents runaway heating due to measurement backaction and we present an analytical model to explain its effectiveness. We showcase our toolbox by studying a two-component BEC using a stochastic mean-field theory, where feedback induces a phase transition between easy-axis ferromagnet and spin-disordered paramagnet phases. We present the steady-state phase diagram as a function of intrinsic and effective spin-dependent interaction strengths. Our result demonstrates that closed-loop quantum control of Bose-Einstein condensates is a powerful tool for quantum engineering in cold-atom systems.}, doi = {10.1103/PhysRevResearch.2.043325}, author = {Hurst, Hilary M. and Guo, Shangjie and Spielman, I. B.} } @article { ISI:000571392500002, title = {Fermion parity gap and exponential ground state degeneracy of the one-dimensional Fermi gas with intrinsic attractive interaction}, journal = {Phys. Rev. B}, volume = {102}, number = {12}, year = {2020}, month = {SEP 21}, pages = {125135}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We examine the properties of a one-dimensional (1D) Fermi gas with attractive intrinsic (Hubbard) interactions in the presence of spin-orbit coupling and Zeeman field by numerically computing the pair binding energy, excitation gap, and susceptibility to local perturbations using the density matrix renormalization group. Such a system can, in principle, be realized in a system of ultracold atoms confined in a 1D optical lattice. We note that, in the presence of spatial interfaces introduced by a smooth parabolic potential, the pair binding and excitation energy of the system decays exponentially with the system size, pointing to the existence of an exponential ground state degeneracy, and is consistent with recent works. However, the susceptibility of the ground state degeneracy of this number-conserving system to local impurities indicates that the energy gap vanishes as a power law with the system size in the presence of local perturbations. We compare this system with the more familiar system of an Ising antiferromagnet in the presence of a transverse field realized with Rydberg atoms and argue that the exponential splitting in the clean number-conserving 1D Fermi system is similar to a phase with only conventional order.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.125135}, author = {Roy, Monalisa Singh and Kumar, Manoranjan and Sau, Jay D. and Tewari, Sumanta} } @article { ISI:000579337200002, title = {Fermi-surface topology and renormalization of bare ellipticity in an interacting anisotropic electron gas}, journal = {Phys. Rev. B}, volume = {102}, number = {16}, year = {2020}, month = {OCT 19}, pages = {161114}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We investigate effects of electron-electron interactions on the shape of the Fermi surface in an anisotropic two-dimensional electron gas using the {\textquoteleft}{\textquoteleft}RPA-GW{{\textquoteright}{\textquoteright}} self-energy approximation. We find that the interacting Fermi surface deviates from an ellipse but not in an arbitrary way. The interacting Fermi surface has only two qualitatively distinct shapes for most values of r(s). The Fermi surface undergoes two distinct transitions between these two shapes as r(s) increases. For larger r(s), the degree of the deviation from an ellipse rapidly increases, but, in general, our theory provides a justification for the widely used elliptical Fermi-surface approximation, even for the interacting system, since the nonelliptic corrections are quantitatively rather small except for very large r(s).}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.161114}, author = {Ahn, Seongjin and Das Sarma, S.} } @article {alavirad_ferromagnetism_2020, title = {Ferromagnetism and its stability from the one-magnon spectrum in twisted bilayer graphene}, journal = {Phys. Rev. B}, volume = {102}, number = {23}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {dec}, abstract = {We study ferromagnetism and its stability in twisted bilayer graphene. We work with a Hubbard-like interaction that corresponds to the screened Coulomb interaction in a well-defined limit where the Thomas-Fermi screening length l(TF) is much larger than monolayer graphene{\textquoteright}s lattice spacing l(g) {\textless}{\textless} l(TF) and much smaller than the moire superlattice{\textquoteright}s spacing l(TF) {\textless}{\textless} l(moire). We show that in the perfectly flat band {\textquotedblleft}chiral{\textquotedblright} limit and at filling fractions +/- 3/4, the saturated ferromagnetic (spin- and valley-polarized) states are ideal ground-state candidates in the large band-gap limit. By assuming a large enough substrate (hBN) induced sublattice potential, the same argument can be applied to filling fractions +/- 1/4. We estimate the regime of stability of the ferromagnetic phase around the chiral limit by studying the exactly calculated spectrum of one-magnon excitations. The instability of the ferromagnetic state is signaled by a negative magnon excitation energy. This approach allows us to deform the results of the idealized chiral model (by increasing the bandwidth and/or modified interactions) toward more realistic systems. Furthermore, we use the low-energy part of the exact one-magnon spectrum to calculate the spin-stiffness of the Goldstone modes throughout the ferromagnetic phase. The calculated value of spin-stiffness can determine the excitation energy of charged skyrmions.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.235123}, author = {Alavirad, Yahya and Sau, Jay} } @article { ISI:000529804100001, title = {Ferromagnetism and superconductivity in twisted double bilayer graphene}, journal = {Phys. Rev. B}, volume = {101}, number = {15}, year = {2020}, month = {APR 30}, pages = {155149}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We present a theory of competing ferromagnetic and superconducting orders in twisted double bilayer graphene. In our theory, ferromagnetism is induced by Coulomb repulsion, while superconductivity with intervalley equal-spin pairing can be mediated by electron-acoustic phonon interactions. We calculate the transition temperatures for ferromagnetism and superconductivity as a function of moire band filling factor, and find that superconducting domes can appear on both the electron and hole sides of the ferromagnetic insulator at half filling. We show that the ferromagnetic insulating gap has a dome shape dependence on the layer potential difference, which provides an explanation to the experimental observation that the ferromagnetic insulator only develops over a finite range of external displacement field. We also verify the stability of the half filled ferromagnetic insulator against two types of collective excitations, i.e., spin magnons and valley magnons.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.101.155149}, author = {Wu, Fengcheng and Das Sarma, Sankar} } @article { ISI:000559739800002, title = {Feshbach Resonances in p-Wave Three-Body Recombination within Fermi-Fermi Mixtures of Open-Shell Li-6 and Closed-Shell Yb-173 Atoms}, journal = {Phys. Rev. X}, volume = {10}, number = {3}, year = {2020}, month = {AUG 14}, pages = {031037}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We report on the observation of magnetic Feshbach resonances in a Fermi-Fermi mixture of ultracold atoms with extreme mass imbalance and on their unique p-wave dominated three-body recombination processes. Our systemconsists of open-shell alkali-metal Li-6 and closed-shell Yb-173 atoms, both spin polarized and held at various temperatures between 1 and 20 mu K. We confirmthat Feshbach resonances in this systemare solely the result of a weak separation-dependent hyperfine coupling between the electronic spin of Li-6 and the nuclear spin of Yb-173. Our analysis also shows that three-body recombination rates are controlled by the identical fermion nature of the mixture, even in the presence of s-wave collisions between the two species and with recombination rate coefficients outside the Wigner threshold regime at our lowest temperature. Specifically, a comparison of experimental and theoretical line shapes of the recombination process indicates that the characteristic asymmetric line shape as a function of applied magnetic field and a maximum recombination rate coefficient that is independent of temperature can only be explained by triatomic collisions with nonzero, p-wave total orbital angular momentum. The resonances can be used to form ultracold doublet ground-state molecules and to simulate quantum superfluidity in mass-imbalanced mixtures.}, issn = {2160-3308}, doi = {10.1103/PhysRevX.10.031037}, author = {Green, Alaina and Li, Hui and Toh, Jun Hui See and Tang, Xinxin and McCormick, Katherine C. and Li, Ming and Tiesinga, Eite and Kotochigova, Svetlana and Gupta, Subhadeep} } @article { ISI:000552576600008, title = {Fidelity of a sequence of SWAP operations on a spin chain}, journal = {Phys. Rev. B}, volume = {102}, number = {3}, year = {2020}, month = {JUL 27}, pages = {035439}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We consider the {\textquoteleft}{\textquoteleft}transport{{\textquoteright}{\textquoteright}} of the state of a spin across a Heisenberg-coupled spin chain via the use of repeated SWAP gates, starting with one of two states-one in which the leftmost spin is down and the others up, and one in which the leftmost two spins are in a singlet state (i.e., they are entangled), and the others are again all up. More specifically, we transport the state of the leftmost spin in the first case and the next-to-leftmost spin in the second to the other end of the chain, and then back again. We accomplish our SWAP operations here by increasing the exchange coupling between the two spins that we operate on from a base value J to a larger value J(SWAP) for a time t = pi(h) over bar /4J(SWAP). We determine the fidelity of this sequence of operations in a number of situations-one in which only nearest-neighbor coupling exists between spins and there is no magnetic dipole-dipole coupling or noise (the most ideal case), one in which we introduce next-nearest-neighbor coupling, but none of the other effects, and one in which all of these effects are present. In the last case, the noise is assumed to be quasistatic, i.e., the exchange couplings are each drawn from a Gaussian distribution, truncated to only nonnegative values. We plot the fidelity as a function of JSWAP to illustrate various effects, namely crosstalk due to coupling to other spins, as well as noise, that are detrimental to our ability to perform a SWAP operation. Our theory should be useful to the ongoing experimental efforts in building semiconductor-based spin quantum computer architectures.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.035439}, author = {Throckmorton, Robert E. and Das Sarma, S.} } @article { ISI:000536153200001, title = {Figures of merit for quantum transducers}, journal = {Quantum Sci. Technol.}, volume = {5}, number = {3}, year = {2020}, month = {JUL}, pages = {034009}, publisher = {IOP PUBLISHING LTD}, type = {Article}, abstract = {Recent technical advances have sparked renewed interest in physical systems that couple simultaneously to different parts of the electromagnetic spectrum, thus enabling transduction of signals between vastly different frequencies at the level of single quanta. Such hybrid systems have demonstrated frequency conversion of classical signals and have the potential of enabling quantum state transfer, e.g., between superconducting circuits and traveling optical signals. This article describes a simple approach for the theoretical characterization of the performance of quantum transducers. Given that, in practice, one cannot attain ideal one-to-one quantum conversion, we explore how imperfections impact the performance of the transducer in various scenarios. We quantify how knowledge of the well-established transducer parameters signal transfer efficiency eta and added noise N suffices to assess its performance in a variety of transduction schemes ranging from classical signal detection to applications for quantum information processing.}, keywords = {quantum sensing, quantum transduction, transduction}, issn = {2058-9565}, doi = {10.1088/2058-9565/ab8962}, author = {Zeuthen, Emil and Schliesser, Albert and Sorensen, Anders S. and Taylor, Jacob M.} } @article { ISI:000535764500002, title = {Filter-free single-photon quantum dot resonance fluorescence in an integrated cavity-waveguide device}, journal = {Optica}, volume = {7}, number = {5}, year = {2020}, month = {MAY 20}, pages = {380-385}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {Semiconductor quantum dots embedded in micropillar cavities are excellent emitters of single photons when pumped resonantly. Often, the same spatial mode is used to both resonantly excite a quantum-dot state and to collect the emitted single photons, requiring cross polarization to reduce the uncoupled scattered laser light. This inherently reduces the source brightness to 50\%. Critically, for some quantum applications the total efficiency from generation to detection must be over 50\%. Here, we demonstrate a resonant-excitation approach to creating single photons that is free of any cross polarization, and in fact any filtering whatsoever. It potentially increases single-photon rates and collection efficiencies, and simplifies operation. This integrated device allows us to resonantly excite single quantum-dot states in several cavities in the plane of the device using connected waveguides, while the cavity-enhanced single-photon fluorescence is directed vertically (off-chip) in a Gaussian mode. We expect this design to be a prototype for larger chip-scale quantum photonics. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement}, issn = {2334-2536}, doi = {10.1364/OPTICA.382273}, author = {Huber, Tobias and Davanco, Marcelo and Muller, Markus and Shuai, Yichen and Gazzano, Olivier and Solomon, Glenn S.} } @article { ISI:000562933100003, title = {Finite-temperature spectroscopy of dirty helical Luttinger liquids}, journal = {Phys. Rev. B}, volume = {102}, number = {8}, year = {2020}, month = {AUG 27}, pages = {085152}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We develop a theory of finite-temperature momentum-resolved tunneling spectroscopy (MRTS) for disordered, interacting, two-dimensional, topological-insulator edges. The MRTS complements conventional electrical transport measurement in characterizing the properties of the helical Luttinger liquid edges. Using the standard bosonization technique, we study low-energy spectral function and the MRTS tunneling current, providing a detailed description controlled by disorder, interaction, and temperature, taking into account Rashba spin-orbit coupling, interedge interaction, and distinct edge velocities. Our theory provides a systematic description of the spectroscopic signals in the MRTS measurement we hope will stimulate future experimental studies on the two-dimensional time-reversal invariant topological insulator.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.085152}, author = {Hsieh, Tzu-Chi and Chou, Yang-Zhi and Radzihovsky, Leo} } @article {hsiang_fluctuation-dissipation_2020, title = {Fluctuation-dissipation relation for open quantum systems in a nonequilibrium steady state}, journal = {Phys. Rev. D}, volume = {102}, number = {10}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {nov}, abstract = {Continuing our work on the nature and existence of fluctuation-dissipation relations (FDR) in linear and nonlinear open quantum systems [J.-T. Hsiang, B. L. Hu, and S.-Y. Lin, Phys. Rev. D 100, 025019 (2019); J.-T. Hsiang, B. L. Hu, S.-Y. Lin, and K. Yamamoto, Phys. Lett. B 795, 694 (2019); J.-T. Hsiang and B. L. Hu, Physics (Utrecht) 1, 430 (2019); J.-T. Hsiang and B. L. Hu, Phys. Rev. D 101, 125003 (2020)], here we consider such relations when a linear system is in a nonequilibrium steady state (NESS). With the model of two-oscillators (considered as a short harmonic chain with the two ends) each connected to a thermal bath of different temperatures we find that when the chain is fully relaxed due to interaction with the baths, the relation that connects the noise kernel and the imaginary part of the dissipation kernel of the chain in one bath does not assume the conventional form for the FDR in equilibrium cases. There exists an additional term we call the {\textquotedblleft}bias current{\textquotedblright} that depends on the difference of the bath{\textquoteright}s initial temperatures and the interoscillator coupling strength. We further show that this term is related to the steady heat flow between the two baths when the system is in an NESS. The ability to know the real-time development of the interheat exchange (between the baths and the end-oscillators) and the intraheat transfer (within the chain) and their dependence on the parameters in the system offers possibilities for quantifiable control, and in the design of quantum heat engines, or thermal devices.}, issn = {2470-0010}, doi = {10.1103/PhysRevD.102.105006}, author = {Hsiang, Jen-Tsung and Hu, Bei-Lok} } @article {hsiang_fluctuation-dissipation_2020-1, title = {Fluctuation-dissipation relation from the nonequilibrium dynamics of a nonlinear open quantum system}, journal = {Phys. Rev. D}, volume = {101}, number = {12}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {jun}, abstract = {Continuing our inquiry into the conditions when fluctuation-dissipation relations (FDR) may appear in the context of nonequilibrium dynamics of open quantum systems (over and beyond the conventional FDR from linear response theory) we turn to non-Gaussian systems and consider this issue for an anharmonic quantum oscillator interacting with a scalar quantum field bath. We present the general nonperturbative expressions for the rate of energy (power) exchange between the anharmonic oscillator and its thermal bath. For the cases that a stable final equilibrium state exists, and the nonstationary components of the two-point functions of the anharmonic oscillator have negligible contributions to the power balance, we can show nonperturbatively that equilibration implies an FDR for the anharmonic oscillator. We then use a weakly anharmonic oscillator as an example to illustrate the validity of those two assumptions and show that in the weak anhamonicity limit, they are satisfied according to our first-order perturbative results..}, issn = {1550-7998}, doi = {10.1103/PhysRevD.101.125003}, author = {Hsiang, Jen-Tsung and Hu, Bei-Lok} } @article { ISI:000551007800002, title = {Fluctuations in Extractable Work Bound the Charging Power of Quantum Batteries}, journal = {Phys. Rev. Lett.}, volume = {125}, number = {4}, year = {2020}, month = {JUL 22}, pages = {040601}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study the connection between the charging power of quantum batteries and the fluctuations of the extractable work. We prove that in order to have a nonzero rate of change of the extractable work, the state rho(W) of the battery cannot be an eigenstatc of a {\textquoteleft}{\textquoteleft}free energy operator,{{\textquoteright}{\textquoteright}} defined by F H-W + beta(-1) log(rho(W)), where H-W is the Hamiltonian of the battery and beta is the inverse temperature of a reference thermal bath with respect to which the extractable work is calculated. We do so by proving that fluctuations in the free energy operator upper bound the charging power of a quantum battery. Our findings also suggest that quantum coherence in the battery enhances the charging process, which we illustrate on a toy model of a heat engine.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.125.040601}, author = {Pedro Garcia-Pintos, Luis and Hamma, Alioscia and del Campo, Adolfo} } @article {sau_anyons_2020, title = {From anyons to {Majoranas}}, journal = {Nat. Rev. Phys.}, volume = {2}, number = {12}, year = {2020}, note = {Place: CAMPUS, 4 CRINAN ST, LONDON, N1 9XW, ENGLAND Publisher: SPRINGERNATURE Type: Editorial Material}, month = {dec}, pages = {667{\textendash}668}, abstract = {Key advances Beam-splitter and interferometric measurements in the quantum Hall regime provide the strongest experimental proof to date of exotic anyonic particles. Individual states inside superconducting vortices, called Caroli-de Gennes-Matricon states, have been experimentally observed in low-density topological superconductors. Access to the Caroli-de Gennes-Matricon states provides a new platform in which anyonic particles may be braided and detected in three dimensional topological superconductors. Anyons, particles that are neither bosons nor fermions, were predicted in the 1980s, but strong experimental evidence for the existence of the simplest type of anyons has only emerged this year. Further theoretical and experimental advances promise to nail the existence of more exotic types of anyons, such as Majorana fermions, which would make topological quantum computation possible. Strong experimental evidence for the existence of the simplest type of anyons (particles that are neither bosons nor fermions) has emerged this year. The next step is to uncover more exotic types of anyons, such as Majorana fermions.

}, doi = {10.1038/s42254-020-00251-9}, author = {Sau, Jay and Simon, Steven and Vishveshwara, Smitha and Williams, James R.} } @article { ISI:000562277400001, title = {Frustration-induced supersolid phases of extended Bose-Hubbard model in the hard-core limit}, journal = {J. Phys.-Condes. Matter}, volume = {32}, number = {45}, year = {2020}, month = {OCT 28}, pages = {455401}, publisher = {IOP PUBLISHING LTD}, type = {Article}, abstract = {We investigate exotic supersolid phases in the extended Bose-Hubbard model with infinite projected entangled-pair state, numerical exact diagonalization, and mean-field theory. We demonstrate that many different supersolid phases can be generated by changing signs of hopping terms, and the interactions along with the frustration of hopping terms are important to stabilize those supersolid states. We argue the effect of frustration introduced by the competition of hopping terms in the supersolid phases from the mean-field point of view. This helps to give a clearer picture of the background mechanism for underlying superfluid/supersolid states to be formed. With this knowledge, we predict and realize thed-wave superfluid, which shares the same pairing symmetry with high-T(c)materials, and its extended phases. We believe that our results contribute to preliminary understanding for desired target phases in the real-world experimental systems.}, keywords = {Bose-Hubbard model, exact diagonalization, phase diagrams, projected entangled pair states, superfluids, supersolids}, issn = {0953-8984}, doi = {10.1088/1361-648X/aba383}, author = {Tu, Wei-Lin and Wu, Huan-Kuang and Suzuki, Takafumi} } @article {morita_full-dimensional_2020, title = {Full-dimensional quantum scattering calculations on ultracold atom-molecule collisions in magnetic fields: {The} role of molecular vibrations}, journal = {Phys. Rev. Res.}, volume = {2}, number = {4}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, abstract = {{Rigorous quantum scattering calculations on ultracold molecular collisions in external fields present an outstanding computational problem due to strongly anisotropic atom-molecule interactions that depend on the relative orientation of the collision partners, as well as on their vibrational degrees of freedom. Here, we present the first numerically exact three-dimensional quantum scattering calculations on strongly anisotropic atom-molecule (Li + CaH) collisions in an external magnetic field based on the parity-adapted total angular momentum representation and a new three-dimensional potential energy surface for the triplet Li-CaH collision complex developed using the unrestricted coupled-cluster method with single, double, and perturbative triple excitations and a large quadruple-zeta-type basis set. We find that while the full three-dimensional treatment is necessary for the accurate description of cold Li(M-S = 1/2) + CaH(v = 0}, doi = {10.1103/PhysRevResearch.2.043294}, author = {Morita, Masato and Klos, Jacek and Tscherbul, V, Timur} } @article {zhu_generation_2020, title = {Generation of thermofield double states and critical ground states with a quantum computer}, journal = {Proc. Natl. Acad. Sci. U. S. A.}, volume = {117}, number = {41}, year = {2020}, note = {Place: 2101 CONSTITUTION AVE NW, WASHINGTON, DC 20418 USA Publisher: NATL ACAD SCIENCES Type: Article}, month = {oct}, pages = {25402{\textendash}25406}, abstract = {Finite-temperature phases of many-body quantum systems are fundamental to phenomena ranging from condensed-matter physics to cosmology, yet they are generally difficult to simulate. Using an ion trap quantum computer and protocols motivated by the quantum approximate optimization algorithm (QAOA), we generate nontrivial thermal quantum states of the transversefield Ising model (TFIM) by preparing thermofield double states at a variety of temperatures. We also prepare the critical state of the TFIM at zero temperature using quantum?classical hybrid optimization. The entanglement structure of thermofield double and critical states plays a key role in the study of black holes, and our work simulates such nontrivial structures on a quantum computer. Moreover, we find that the variational quantum circuits exhibit noise thresholds above which the lowest-depth QAOA circuits provide the best results.}, keywords = {Ising model, quantum computing, quantum simulation, thermofield double state, trapped ions}, issn = {0027-8424}, doi = {10.1073/pnas.2006337117}, author = {Zhu, D. and Johri, S. and Linke, N. M. and Landsman, K. A. and Alderete, C. Huerta and Nguyen, N. H. and Matsuura, A. Y. and Hsieh, T. H. and Monroe, C.} } @article { ISI:000506582800005, title = {Generic quantized zero-bias conductance peaks in superconductor-semiconductor hybrid structures}, journal = {Phys. Rev. B}, volume = {101}, number = {2}, year = {2020}, month = {JAN 8}, pages = {024506}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We show theoretically that quantized zero-bias conductance peaks should be ubiquitous in superconductor-semiconductor hybrids by employing a zero-dimensional random matrix model with continuous tuning parameters. We demonstrate that a normal metal-superconductor (NS) junction conductance spectra can be generically obtained in this model replicating all features seen in recent experimental results. The theoretical quantized conductance peaks, which explicitly do not arise from spatially isolated Majorana zero modes, are easily found by preparing a contour plot of conductance over several independent tuning parameters, mimicking the effect of Zeeman splitting and voltages on gates near the junction. This suggests that, even stable apparently quantized conductance peaks need not correspond to isolated Majorana modes; rather, the a priori expectation should be that such quantized peaks generically occupy a significant fraction of the high-dimensional tuning parameter space that characterizes the NS tunneling experiments.

}, issn = {2469-9950}, doi = {10.1103/PhysRevB.101.024506}, author = {Pan, Haining and Cole, William S. and Sau, Jay D. and Das Sarma, Sankar} } @article {tenasini_giant_2020, title = {Giant anomalous {Hall} effect in quasi-two-dimensional layered antiferromagnet {Co1}/{3NbS2}}, journal = {Phys. Rev. Res.}, volume = {2}, number = {2}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {apr}, abstract = {The discovery of the anomalous Hall effect (AHE) in bulk metallic antiferromagnets (AFMs) motivates the search of the same phenomenon in two-dimensional (2D) systems, where a quantized anomalous Hall conductance can, in principle, be observed. Here we present experiments on microfabricated devices based on Co1/3NbS2, a layered AFM that was recently found to exhibit AHE in bulk crystals below the Neel temperature T-N = 29 K. Transport measurements reveal a pronounced resistivity anisotropy, indicating that upon lowering temperature the electronic coupling between individual atomic layers is increasingly suppressed. The experiments also show an extremely large anomalous Hall conductivity of approximately 400 S/cm, more than one order of magnitude larger than in the bulk, which demonstrates the importance of studying the AHE in small exfoliated crystals, less affected by crystalline defects. Interestingly, the corresponding anomalous Hall conductance, when normalized to the number of contributing atomic planes, is similar to 0.6 e(2)/h per layer, approaching the value expected for the quantized anomalous Hall effect. The observed strong anisotropy of transport and the very large anomalous Hall conductance per layer make the properties of Co1/3NbS2 compatible with the presence of partially filled topologically nontrivial 2D bands originating from the magnetic superstructure of the antiferromagnetic state. Isolating atomically thin layers of this material and controlling their charge density may therefore provide a viable route to reveal the occurrence of the quantized AHE in a 2D AFM.

}, doi = {10.1103/PhysRevResearch.2.023051}, author = {Tenasini, Giulia and Martino, Edoardo and Ubrig, Nicolas and Ghimire, Nirmal J. and Berger, Helmuth and Zaharko, Oksana and Wu, Fengcheng and Mitchell, J. F. and Martin, Ivar and Forro, Laszlo and Morpurgo, Alberto F.} } @article { ISI:000524530000001, title = {Ground-state energy estimation of the water molecule on a trapped-ion quantum computer}, journal = {npj Quantum Inform.}, volume = {6}, number = {1}, year = {2020}, month = {APR 3}, pages = {33}, publisher = {NATURE PUBLISHING GROUP}, type = {Article}, abstract = {Quantum computing leverages the quantum resources of superposition and entanglement to efficiently solve computational problems considered intractable for classical computers. Examples include calculating molecular and nuclear structure, simulating strongly interacting electron systems, and modeling aspects of material function. While substantial theoretical advances have been made in mapping these problems to quantum algorithms, there remains a large gap between the resource requirements for solving such problems and the capabilities of currently available quantum hardware. Bridging this gap will require a co-design approach, where the expression of algorithms is developed in conjunction with the hardware itself to optimize execution. Here we describe an extensible co-design framework for solving chemistry problems on a trapped-ion quantum computer and apply it to estimating the ground-state energy of the water molecule using the variational quantum eigensolver (VQE) method. The controllability of the trapped-ion quantum computer enables robust energy estimates using the prepared VQE ansatz states. The systematic and statistical errors are comparable to the chemical accuracy, which is the target threshold necessary for predicting the rates of chemical reaction dynamics, without resorting to any error mitigation techniques based on Richardson extrapolation.}, doi = {10.1038/s41534-020-0259-3}, author = {Nam, Yunseong and Chen, Jwo-Sy and Pisenti, Neal C. and Wright, Kenneth and Delaney, Conor and Maslov, Dmitri and Brown, Kenneth R. and Allen, Stewart and Amini, Jason M. and Apisdorf, Joel and Beck, Kristin M. and Blinov, Aleksey and Chaplin, Vandiver and Chmielewski, Mika and Collins, Coleman and Debnath, Shantanu and Hudek, Kai M. and Ducore, Andrew M. and Keesan, Matthew and Kreikemeier, Sarah M. and Mizrahi, Jonathan and Solomon, Phil and Williams, Mike and Wong-Campos, Jaime David and Moehring, David and Monroe, Christopher and Kim, Jungsang} } @article { ISI:000535764500019, title = {Guiding and confining of light in a two-dimensional synthetic space using electric fields}, journal = {Optica}, volume = {7}, number = {5}, year = {2020}, month = {MAY 20}, pages = {506-513}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {Synthetic dimensions provide a promising platform for photonic quantum simulations. Manipulating the flow of photons in these dimensions requires an electric field. However, photons do not have charge and do not directly interact with electric fields. Therefore, alternative approaches are needed to realize electric fields in photonics. One approach is to use engineered gauge fields that can mimic the effect of electric fields and produce the same dynamical behavior. Here, we demonstrate such an electric field for photons propagating in a two-dimensional synthetic space. Generation of electric fields in a two-dimensional synthetic lattice provides the possibility to guide photons and to trap them through the creation of quantum confined structures. We achieve this using a linearly time-varying gauge field generated by direction-dependent phase modulations. We show that the generated electric field leads to Bloch oscillations and the revival of the state after a certain number of steps dependent on the field strength. We measure the probability of the revival and demonstrate a good agreement between the observed values and the theoretically predicted results. Furthermore, by applying a nonuniform electric field, we show the possibility of waveguiding photons. Ultimately, our results open up new opportunities for manipulating the propagation of photons with potential applications in photonic quantum simulations. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement}, issn = {2334-2536}, doi = {10.1364/OPTICA.386347}, author = {Chalabi, Hamidreza and Barik, Sabyasachi and Mittal, Sunil and Murphy, Thomas E. and Hafezi, Mohammad and Waks, Edo} } @article {16891, title = {Hierarchy of Linear Light Cones with Long-Range Interactions}, journal = {Phys. Rev. X}, volume = {10}, year = {2020}, month = {Jul}, pages = {031009}, doi = {10.1103/PhysRevX.10.031009}, url = {https://link.aps.org/doi/10.1103/PhysRevX.10.031009}, author = {Tran, Minh C. and Chen, Chi-Fang and Ehrenberg, Adam and Guo, Andrew Y. and Deshpande, Abhinav and Hong, Yifan and Gong, Zhe-Xuan and Gorshkov, Alexey V. and Lucas, Andrew} } @article { ISI:000562320800002, title = {Higgs-like modes in two-dimensional spatially indirect exciton condensates}, journal = {Phys. Rev. B}, volume = {102}, number = {7}, year = {2020}, month = {AUG 25}, pages = {075136}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Higgs-like modes in condensed-matter physics have drawn attention because of analogies to the Higgs bosons of particle physics. Here we use a microscopic time-dependent mean-field theory to study the collective mode spectra of two-dimensional spatially indirect exciton (electron-hole pair) condensates, focusing on the Higgs-like modes, i.e., those that have a large weight in electron-hole pair amplitude response functions. We find that in the low exciton density (Bose-Einstein condensate) limit, the dominant Higgs-like modes of spatially indirect exciton condensates correspond to adding electron-hole pairs that are orthogonal to the condensed pair state. We comment on the previously studied Higgs-like collective excitations of superconductors in light of this finding.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.075136}, author = {Xue, Fei and Wu, Fengcheng and MacDonald, A. H.} } @conference {singh_high-q_2020, title = {High-{Q} {Nanomechanical} {Resonators} for {Optomechanical} {Sensing} {Beyond} the {Standard} {Quantum} {Limit}}, booktitle = {Conference on Lasers and Electro-Optics (CLEO)}, series = {Conference on {Lasers} and {Electro}-{Optics}}, year = {2020}, note = {Backup Publisher: IEEE ISSN: 2160-9020 Type: Proceedings Paper}, publisher = {IEEE}, organization = {IEEE}, abstract = {We fabricate high-stress silicon and silicon-nitride based nanomechanical string resonators to study quantum optomechanical interactions. We use phononic band-gap engineering techniques to minimize mechanical energy dissipation in the out-of-plane defect mode of the resonator. (C) 2020 The Author(s)

}, isbn = {978-1-943580-76-7}, author = {Singh, Robinjeet and Purdy, Thomas P.} } @article {kuehn_high_2020, title = {High {Resolution} {Photoexcitation} {Measurements} {Exacerbate} the {Long}-{Standing} {Fe} {XVII} {Oscillator} {Strength} {Problem}, journal = {Phys. Rev. Lett.}, volume = {124}, number = {22}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {jun}, abstract = {For more than 40 years, most astrophysical observations and laboratory studies of two key soft x-ray diagnostic 2p - 3d transitions, 3C and 3D, in Fe XVII ions found oscillator strength ratios f(3C)/f(3D) disagreeing with theory, but uncertainties had precluded definitive statements on this much studied conundrum. Here, we resonantly excite these lines using synchrotron radiation at PETRA III, and reach, at a millionfold lower photon intensities, a 10 times higher spectral resolution, and 3 times smaller uncertainty than earlier work. Our final result of f(3C)/f(3D) = 3.09(8)(6) supports many of the earlier clean astrophysical and laboratory observations, while departing by five sigmas from our own newest large-scale ab initio calculations, and excluding all proposed explanations, including those invoking nonlinear effects and population transfers.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.124.225001}, author = {Kuehn, Steffen and Shah, Chintan and Lopez-Urrutia, Jose R. Crespo and Fujii, Keisuke and Steinbruegge, Rene and Stierhof, Jakob and Togawa, Moto and Harman, Zoltan and Oreshkina, Natalia S. and Cheung, Charles and Kozlov, Mikhail G. and Porsev, Sergey G. and Safronova, Marianna S. and Berengut, Julian C. and Rosner, Michael and Bissinger, Matthias and Ballhausen, Ralf and Hell, Natalie and Park, SungNam and Chung, Moses and Hoesch, Moritz and Seltmann, Joern and Surzhykov, Andrey S. and Yerokhin, Vladimir A. and Wilms, Joern and Porter, F. Scott and Stoehlker, Thomas and Keitel, Christoph H. and Pfeifer, Thomas and Brown, V, Gregory and Leutenegger, Maurice A. and Bernitt, Sven} } @article { ISI:000565455100005, title = {Higher-order topological Dirac superconductors}, journal = {Phys. Rev. B}, volume = {102}, number = {9}, year = {2020}, month = {SEP 3}, pages = {094503}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We introduce higher-order topological Dirac superconductor (HOTDSC) as a gapless topological phase of matter in three dimensions, which extends the notion of Dirac phase to a higher-order topological version. Topologically distinct from the traditional topological superconductors and known Dirac superconductors, a HOTDSC features Majorana hinge modes between adjacent surfaces, which are direct consequences of the symmetry-protected higher-order band topology manifesting in the system. Specifically, we show that rotational, spatial inversion, and time-reversal symmetries together protect the coexistence of bulk Dirac nodes and hinge Majorana modes in a seamless way. We define a set of topological indices that fully characterizes the HOTDSC. We further show that a practical way to realize the HOTDSC phase is to introduce unconventional odd-parity pairing to a three-dimensional Dirac semimetal while preserving the necessary symmetries. As a concrete demonstration of our idea, we construct a corresponding minimal lattice model for HOTDSC obeying the symmetry constraints. Our model exhibits the expected topological invariants in the bulk and the defining spectroscopic features on an open geometry, as we explicitly verify both analytically and numerically. Remarkably, the HOTDSC phase offers an example of a {\textquoteleft}{\textquoteleft}higher-order topological quantum critical point, which enables realizations of various higher-order topological phases under different symmetry-breaking patterns. In particular, by breaking the inversion symmetry of a HOTDSC, we arrive at a higher-order Weyl superconductor, which is yet another gapless topological state that exhibits hybrid higher-order topology.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.094503}, author = {Zhang, Rui-Xing and Hsu, Yi-Ting and Das Sarma, S.} } @article { ISI:000535205600016, title = {Hilbert-Space Fragmentation from Strict Confinement}, journal = {Phys. Rev. Lett.}, volume = {124}, number = {20}, year = {2020}, month = {MAY 22}, pages = {207602}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study one-dimensional spin-1/2 models in which strict confinement of Ising domain walls leads to the fragmentation of Hilbert space into exponentially many disconnected subspaces. Whereas most previous works emphasize dipole moment conservation as an essential ingredient for such fragmentation, we instead require two commuting U(1) conserved quantities associated with the total domain-wall number and the total magnetization. The latter arises naturally from the confinement of domain walls. Remarkably, while some connected components of the Hilbert space thermalize, others are integrable by Bethe ansatz. We further demonstrate how this Hilbert-space fragmentation pattern arises perturbatively in the confining limit of Z(2) gauge theory coupled to fermionic matter, leading to a hierarchy of timescales for motion of the fermions. This model can be realized experimentally in two complementary settings.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.124.207602}, author = {Yang, Zhi-Cheng and Liu, Fangli and Gorshkov, V, Alexey and Iadecola, Thomas} } @article {chou_hofstadter_2020, title = {Hofstadter butterfly and {Floquet} topological insulators in minimally twisted bilayer graphene}, journal = {Phys. Rev. Res.}, volume = {2}, number = {3}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {aug}, abstract = {We theoretically study the Hofstadter butterfly of a triangular network model in minimally twisted bilayer graphene. The band structure manifests periodicity in energy, mimicking that of Floquet systems. The butterfly diagrams provide fingerprints of the model parameters and reveal the hidden band topology. In a strong magnetic field, we establish that minimally twisted bilayer graphene realizes low-energy Floquet topological insulators (FTIs) carrying zero Chern number, while hosting chiral edge states in bulk gaps. We identify the FTIs by analyzing the nontrivial spectral flow in the Hofstadter butterfly, and by explicitly computing the chiral edge states. Our theory paves the way for an effective practical realization of FTIs in equilibrium solid-state systems.}, doi = {10.1103/PhysRevResearch.2.033271}, author = {Chou, Yang-Zhi and Wu, Fengcheng and Das Sarma, Sankar} } @article {elshaari_hybrid_2020, title = {Hybrid integrated quantum photonic circuits}, journal = {Nat. Photonics}, volume = {14}, number = {5}, year = {2020}, note = {Place: MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND Publisher: NATURE PUBLISHING GROUP Type: Review}, month = {may}, pages = {285{\textendash}298}, abstract = {The Review summarizes the progress of hybrid quantum photonics integration in terms of its important design considerations and fabrication approaches, and highlights some successful realizations of key physical resources for building integrated quantum devices, such as quantum teleporters, quantum repeaters and quantum simulators. Recent developments in chip-based photonic quantum circuits have radically impacted quantum information processing. However, it is challenging for monolithic photonic platforms to meet the stringent demands of most quantum applications. Hybrid platforms combining different photonic technologies in a single functional unit have great potential to overcome the limitations of monolithic photonic circuits. Our Review summarizes the progress of hybrid quantum photonics integration, discusses important design considerations, including optical connectivity and operation conditions, and highlights several successful realizations of key physical resources for building a quantum teleporter. We conclude by discussing the roadmap for realizing future advanced large-scale hybrid devices, beyond the solid-state platform, which hold great potential for quantum information applications.}, issn = {1749-4885}, doi = {10.1038/s41566-020-0609-x}, author = {Elshaari, Ali W. and Pernice, Wolfram and Srinivasan, Kartik and Benson, Oliver and Zwiller, Val} } @article { ISI:000528219500006, title = {Hybrid integration methods for on-chip quantum photonics}, journal = {Optica}, volume = {7}, number = {4}, year = {2020}, month = {APR 20}, pages = {291-308}, publisher = {OPTICAL SOC AMER}, type = {Review}, abstract = {The goal of integrated quantum photonics is to combine components for the generation, manipulation, and detection of nonclassical light in a phase-stable and efficient platform. Solid-state quantum emitters have recently reached outstanding performance as single-photon sources. In parallel, photonic integrated circuits have been advanced to the point that thousands of components can be controlled on a chip with high efficiency and phase stability. Consequently, researchers are now beginning to combine these leading quantum emitters and photonic integrated circuit platforms to realize the best properties of each technology. In this paper, we review recent advances in integrated quantum photonics based on such hybrid systems. Although hybrid integration solves many limitations of individual platforms, it also introduces new challenges that arise from interfacing different materials. We review various issues in solid-state quantum emitters and photonic integrated circuits, the hybrid integration techniques that bridge these two systems, and methods for chip-based manipulation of photons and emitters. Finally, we discuss the remaining challenges and future prospects of on-chip quantum photonics with integrated quantum emitters. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement}, issn = {2334-2536}, doi = {10.1364/OPTICA.384118}, author = {Kim, Je-Hyung and Aghaeimeibodi, Shahriar and Carolan, Jacques and Englund, Dirk and Waks, Edo} } @article {zhiqiang_hyperfine-mediated_2020, title = {Hyperfine-mediated effects in a {Lu}+ optical clock}, journal = {Phys. Rev. A}, volume = {102}, number = {5}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {nov}, abstract = {We consider hyperfine-mediated effects for clock transitions in Lu-176(+). Mixing of fine-structure levels due to the hyperfine interaction brings about modifications to the Lande g-factors and the quadrupole moment for a given state. Explicit expressions are derived for both the g-factor and quadrupole corrections, for which leading-order terms arise from the nuclear magnetic dipole coupling. High accuracy measurements of the g-factors for the S-1(0) and D-3(1) hyperfine levels are carried out, and they provide an experimental determination of the leading-order correction terms.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.102.052834}, author = {Zhiqiang, Zhang and Arnold, K. J. and Kaewuam, R. and Safronova, M. S. and Barrett, M. D.} } @article {16901, title = {Imaging viscous flow of the Dirac fluid in graphene}, journal = {Nature}, volume = {583}, year = {2020}, month = {Jul}, pages = {537-541}, abstract = {The electron{\textendash}hole plasma in charge-neutral graphene is predicted to realize a quantum critical system in which electrical transport features a universal hydrodynamic description, even at room temperature1,2. This quantum critical {\textquoteleft}Dirac fluid{\textquoteright} is expected to have a shear viscosity close to a minimum bound3,4, with an interparticle scattering rate saturating1 at the Planckian time, the shortest possible timescale for particles to relax. Although electrical transport measurements at finite carrier density are consistent with hydrodynamic electron flow in graphene5{\textendash}8, a clear demonstration of viscous flow at the charge-neutrality point remains elusive. Here we directly image viscous Dirac fluid flow in graphene at room temperature by measuring the associated stray magnetic field. Nanoscale magnetic imaging is performed using quantum spin magnetometers realized with nitrogen vacancy centres in diamond. Scanning single-spin and wide-field magnetometry reveal a parabolic Poiseuille profile for electron flow in a high-mobility graphene channel near the charge-neutrality point, establishing the viscous transport of the Dirac fluid. This measurement is in contrast to the conventional uniform flow profile imaged in a metallic conductor and also in a low-mobility graphene channel. Via combined imaging and transport measurements, we obtain viscosity and scattering rates, and observe that these quantities are comparable to the universal values expected at quantum criticality. This finding establishes a nearly ideal electron fluid in charge-neutral, high-mobility graphene at room temperature4. Our results will enable the study of hydrodynamic transport in quantum critical fluids relevant to strongly correlated electrons in high-temperature superconductors9. This work also highlights the capability of quantum spin magnetometers to probe correlated electronic phenomena at the nanoscale.

}, issn = {1476-4687}, doi = {10.1038/s41586-020-2507-2}, url = {https://doi.org/10.1038/s41586-020-2507-2}, author = {Ku, Mark J. H. and Zhou, Tony X. and Li, Qing and Shin, Young J. and Shi, Jing K. and Burch, Claire and Anderson, Laurel E. and Pierce, Andrew T. and Xie, Yonglong and Hamo, Assaf and Vool, Uri and Zhang, Huiliang and Casola, Francesco and Taniguchi, Takashi and Watanabe, Kenji and Fogler, Michael M. and Kim, Philip and Yacoby, Amir and Walsworth, Ronald L.} } @article {li_improved_2020, title = {Improved coupled-mode theory for high-index-contrast photonic platforms}, journal = {Phys. Rev. A}, volume = {102}, number = {6}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {dec}, abstract = {Coupled-mode theory (CMT) has been widely used in optics and photonics design. Despite its popularity, several different formulations of CMT exist in the literature, and their applicable range is not entirely clear, in particular when it comes to high-index-contrast photonics platforms. Here we propose an improved formulation of CMT and demonstrate its superior performance through numerical simulations that compare CMT-derived quantities with supermode calculations and full wave propagation simulations. In particular, application of the improved CMT to asymmetric waveguides reveals a necessary correction in the conventional phase matching condition for high-index-contrast systems, which could lead to more accurate photonic circuit designs involving asymmetric elements.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.102.063506}, author = {Li, Qing and Moille, Gregory and Taheri, Hossein and Adibi, Ali and Srinivasan, Kartik} } @article {hwang_impurity-scattering-induced_2020, title = {Impurity-scattering-induced carrier transport in twisted bilayer graphene}, journal = {Phys. Rev. Res.}, volume = {2}, number = {1}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {mar}, abstract = {We theoretically calculate the impurity-scattering-induced resistivity of twisted bilayer graphene at low twist angles where the graphene Fermi velocity is strongly suppressed. We consider, as a function of carrier density, twist angle, and temperature, both long-ranged Coulomb scattering and short-ranged defect scattering within a Boltzmann theory relaxation time approach. For experimentally relevant disorder, impurity scattering contributes a resistivity comparable to (much larger than) the phonon scattering contribution at high (low) temperatures. Decreasing twist angle leads to larger resistivity, and in general, the resistivity increases (decreases) with increasing temperature (carrier density). Inclusion of the van Hove singularity in the theory leads to a strong increase in the resistivity at higher densities, where the chemical potential is close to a van Hove singularity, leading to an apparent density-dependent plateau-type structure in the resistivity, which has been observed in recent transport experiments. We also show that the Matthiessen{\textquoteright}s rule is strongly violated in twisted bilayer graphene at low twist angles.}, doi = {10.1103/PhysRevResearch.2.013342}, author = {Hwang, E. H. and Das Sarma, S.} } @article { ISI:000522116800007, title = {Incorporating the Stern-Gerlach delayed-choice quantum eraser into the undergraduate quantum mechanics curriculum}, journal = {Am. J. Phys.}, volume = {88}, number = {4}, year = {2020}, month = {APR}, pages = {298-307}, publisher = {AMER INST PHYSICS}, type = {Article}, abstract = {As {\textquoteleft}{\textquoteleft}Stern-Gerlach first{{\textquoteright}{\textquoteright}} becomes increasingly popular in the undergraduate quantum mechanics curriculum, we show how one can extend the treatment found in conventional textbooks to cover some exciting new quantum phenomena. Namely, we illustrate how one can describe a delayed choice variant of the quantum eraser which is realized within the Stern-Gerlach framework. Covering this material allows the instructor to reinforce notions of changes in basis functions, quantum superpositions, quantum measurements, and the complementarity principle as expressed in whether we know {\textquoteleft}{\textquoteleft}which-way{{\textquoteright}{\textquoteright}} information or not. It also allows the instructor to dispel common misconceptions of when a measurement occurs and when a system is in a superposition of states.}, issn = {0002-9505}, doi = {10.1119/10.0000519}, author = {Courtney, William F. and Vieira, Lucas B. and Julienne, Paul S. and Freericks, James K.} } @article { ISI:000575024200001, title = {Infrared fixed points of higher-spin fermions in topological semimetals}, journal = {Phys. Rev. B}, volume = {102}, number = {15}, year = {2020}, month = {OCT 5}, pages = {155104}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We determine the fate of interacting fermions described by the Hamiltonian H = p . J in three-dimensional topological semimetals with linear band crossing, where p is momentum and J are the spin- j matrices for half-integer pseudospin j >= 3/2. While weak short-range interactions are irrelevant at the crossing point due to the vanishing density of states, weak long-range Coulomb interactions lead to a renormalization of the band structure. Using a self-consistent perturbative renormalization group approach, we show that band crossings of the type p . J are unstable for j >= 7/2. Instead, through an intriguing interplay between cubic crystal symmetry, band topology, and interaction effects, the system is attracted to a variety of infrared fixed points. We also unravel several other properties of higher-spin fermions for general j, such as the relation between fermion self-energy and free energy, or the vanishing of the renormalized charge. An O(3) symmetric fixed point composed of equal chirality Weyl fermions is stable for j <= 7/2 and very likely so for all j. We then explore the rich fixed point structure for j = 5/2 in detail. We find additional attractive fixed points with enhanced 0(3) symmetry that host both emergent Weyl or massless Dirac fermions, and identify a puzzling, infrared stable, anisotropic fixed point without enhanced symmetry in close analogy to the known case of j = 3/2.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.155104}, author = {Boettcher, Igor} } @article {16956, title = {Instantaneous braids and Dehn twists in topologically ordered states}, journal = {Phys. Rev. B}, volume = {102}, year = {2020}, month = {Aug}, pages = {075105}, doi = {10.1103/PhysRevB.102.075105}, url = {https://link.aps.org/doi/10.1103/PhysRevB.102.075105}, author = {Zhu, Guanyu and Lavasani, Ali and Barkeshli, Maissam} } @conference {rao_integrated_2020, title = {Integrated {Photonic} {Interposers} for {Processing} {Octave}-{Spanning} {Microresonator} {Frequency} {Combs}}, booktitle = {Conference on Lasers and Electro-Optics (CLEO)}, series = {Conference on {Lasers} and {Electro}-{Optics}}, year = {2020}, note = {Backup Publisher: IEEE ISSN: 2160-9020 Type: Proceedings Paper}, publisher = {IEEE}, organization = {IEEE}, abstract = {We demonstrate multiple silicon-nitride nanophotonic elements for on-chip processing of octave-spanning microresonator frequency combs. Dichroic filters, multimode interferometers, and tunable add-drop microring filters are shown along with soliton microcombs generated on a bilayer photonic chip. (C) 2020 The Author(s)

}, isbn = {978-1-943580-76-7}, author = {Rao, Ashutosh and Moille, Gregory and Lu, Xiyuan and Sacchetto, Davide and Geiselmann, Michael and Zervas, Michael and Papp, Scott and Bowers, John and Srinivasan, Kartik} } @conference {dutta_integrated_2020, title = {An {Integrated} {Photonic} {Platform} for {Rare}-{Earth} {Ions} in {Thin} {Film} {Lithium} {Niobate}}, booktitle = {Conference on Lasers and Electro-Optics (CLEO)}, series = {Conference on {Lasers} and {Electro}-{Optics}}, year = {2020}, note = {Backup Publisher: IEEE ISSN: 2160-9020 Type: Proceedings Paper}, publisher = {IEEE}, organization = {IEEE}, abstract = {We demonstrate an integrated photonic platform for rare earth ions in thin film lithium niobate. The ions in the thin film retain bulk like optical properties. This paves way for a new generation of highly scalable, active optoelectronic devices with applications to both classical and quantum optics. (C) 2020 The Author(s)

}, isbn = {978-1-943580-76-7}, author = {Dutta, Subhojit and Goldschmidt, Elizabeth A. and Barik, Sabyasachi and Saha, Uday and Waks, Edo} } @article { ISI:000507151600097, title = {Integrated Photonic Platform for Rare-Earth Ions in Thin Film Lithium Niobate}, journal = {Nano Lett.}, volume = {20}, number = {1}, year = {2020}, month = {JAN}, pages = {741-747}, publisher = {AMER CHEMICAL SOC}, type = {Article}, abstract = {Rare-earth ion ensembles doped in single crystals are a promising materials system with widespread applications in optical signal processing, lasing, and quantum information processing. Incorporating rare-earth ions into integrated photonic devices could enable compact lasers and modulators, as well as on-chip optical quantum memories for classical and quantum optical applications. To this end, a thin film single crystalline wafer structure that is compatible with planar fabrication of integrated photonic devices would be highly desirable. However, incorporating rare-earth ions into a thin film form-factor while preserving their optical properties has proven challenging. We demonstrate an integrated photonic platform for rare-earth ions doped in a single crystalline thin film lithium niobate on insulator. The thin film is composed of lithium niobate doped with Tm3+. The ions in the thin film exhibit optical lifetimes identical to those measured in bulk crystals. We show narrow spectral holes in a thin film waveguide that require up to 2 orders of magnitude lower power to generate than previously reported bulk waveguides. Our results pave the way for scalable on-chip lasers, optical signal processing devices, and integrated optical quantum memories.}, keywords = {integrated photonics, optical signal processing, Rare-earth ions, spectral hole burning quantum information processing, thin film lithium niobate}, issn = {1530-6984}, doi = {10.1021/acs.nanolett.9b04679}, author = {Dutta, Subhojit and Goldschmidt, Elizabeth A. and Barik, Sabyasachi and Saha, Uday and Waks, Edo} } @article {hu_interacting_2020, title = {Interacting topological mirror excitonic insulator in one dimension}, journal = {Phys. Rev. B}, volume = {102}, number = {23}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {dec}, abstract = {We introduce the topological mirror excitonic insulator as a new type of interacting topological crystalline phase in one dimension. Its mirror-symmetry-protected topological properties are driven by exciton physics, and it manifests in the quantized bulk polarization and half-charge modes on the boundary. And the bosonization analysis is performed to demonstrate its robustness against strong correlation effects in one dimension. Besides, we also show that Rashba nanowires and Dirac semimetal nanowires could provide ideal experimental platforms to realize this new topological mirror excitonic insulating state. Its experimental consequences, such as quantized tunneling conductance in the tunneling measurement, are also discussed.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.235115}, author = {Hu, Lun-Hui and Zhang, Rui-Xing and Zhang, Fu-Chun and Wu, Congjun} } @article {16681, title = {Interplay of Topology and Electron-Electron Interactions in Rarita-Schwinger-Weyl semimetals}, journal = {Phys. Rev. Lett.}, volume = {124}, year = {2020}, month = {Mar}, pages = {127602}, abstract = {We study, for the first time, the effects of strong short-range electron-electron interactions in generic Rarita-Schwinger-Weyl semimetals hosting spin-3/2\ electrons with linear dispersion at a fourfold band crossing point. The emergence of this novel quasiparticle, which is absent in high-energy physics, has recently been confirmed experimentally in the solid state. We combine symmetry considerations and a perturbative renormalization group analysis to discern three interacting phases that are prone to emerge in the strongly correlated regime: The chiral topological semimetal breaks a\ Z2\ symmetry and features four Weyl nodes of monopole charge\ +1\ located at vertices of a tetrahedron in momentum space. The\ s-wave superconducting state opens a Majorana mass gap for the fermions and is the leading superconducting instability. The Weyl semimetal phase removes the fourfold degeneracy and creates two Weyl nodes with either equal or opposite chirality depending on the anisotropy of the band structure. We find that symmetry breaking occurs at weaker coupling if the total monopole charge remains constant across the transition.

}, doi = {10.1103/PhysRevLett.124.127602}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.124.127602}, author = {Boettcher, Igor} } @article { ISI:000562003800006, title = {Inversion-protected Higher-order Topological Superconductivity in Monolayer WTe2}, journal = {Phys. Rev. Lett.}, volume = {125}, number = {9}, year = {2020}, month = {AUG 24}, pages = {097001}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Monolayer WTe2, a centrosymmetric transition metal dichacogenide, has recently been established as a quantum spin Hall insulator and found superconducting upon gating. Here we study the pairing symmetry and topological nature of superconducting WTe2 with a microscopic model at mean-field level. Surprisingly, we find that the spin-triplet phases in our phase diagram all host Majorana modes localized on two opposite corners. Even when the conventional pairing is favored, we find that an intermediate inplane magnetic field exceeding the Pauli limit stabilizes an unconventional equal-spin pairing aligning with the field, which also hosts Majorana corner modes. Motivated by our findings, we obtain a recipe for two-dimensional superconductors featuring {\textquoteleft}{\textquoteleft}higher-order topology{{\textquoteright}{\textquoteright}} from the boundary perspective. Generally, a superconducting inversion-symmetric quantum spin Hall material whose normal-state Fermi surface is away from high-symmetry points, such as gated monolayer WTe2, hosts Majorana corner modes if the superconductivity is parity-odd. We further point out that this higher-order phase is an inversion-protected topological crystalline superconductor and study the bulk-boundary correspondence. Finally, we discuss possible experiments for probing the Majorana corner modes. Our findings suggest superconducting monolayer WTe, is a playground for higher-order topological superconductivity and possibly the first material realization for inversion-protected Majorana corner modes without utilizing proximity effect.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.125.097001}, author = {Hsu, Yi-Ting and Cole, William S. and Zhang, Rui-Xing and Sau, Jay D.} } @conference {sabines-chesterking_klyshko_2020, title = {Klyshko efficiency optimization using a genetic algorithm}, booktitle = {Conference on Lasers and Electro-Optics (CLEO)}, series = {Conference on {Lasers} and {Electro}-{Optics}}, year = {2020}, note = {Backup Publisher: IEEE ISSN: 2160-9020 Type: Proceedings Paper}, publisher = {IEEE}, organization = {IEEE}, address = {Conference on Lasers and Electro-Optics (CLEO)}, abstract = {We use a spatial light modulator and a genetic algorithm to manipulate the spatial profile of the pump beam of a down-conversion source in order to improve its Klyshko efficiency. (c) 2020 The Author(s)

}, isbn = {978-1-943580-76-7}, author = {Sabines-Chesterking, Javier and Moreau, Paul-Antoine and McMillan, Alex and Fickler, Robert and Rarity, John and Matthews, Jonathan} } @article {pasnoori_kondo_2020, title = {Kondo impurity at the edge of a superconducting wire}, journal = {Phys. Rev. Res.}, volume = {2}, number = {1}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {jan}, abstract = {Quantum impurity models are prevalent throughout many body physics, providing some prime examples of strongly correlated systems. Aside from being of great interest in themselves, they can provide deep insight into the effects of strong correlations in general. The classic example is the Kondo model wherein a magnetic impurity is screened at low energies by a noninteracting metallic bath. Here we consider a magnetic impurity coupled to a quantum wire with pairing interaction which dynamically generates a mass gap. Using Bethe ansatz, we solve the system exactly finding that it exhibits both screened and unscreened phases for an antiferromagnetic impurity. We determine the ground-state density of states and magnetization in both phases as well as the excitations. In contrast to the well studied case of magnetic impurities in superconductors, we find that there are no intragap bound states in the spectrum. The phase transition is not associated to a level crossing but with quantum fluctuations.}, doi = {10.1103/PhysRevResearch.2.013006}, author = {Pasnoori, Parameshwar R. and Rylands, Colin and Andrei, Natan} } @article {jian_landau_2020, title = {Landau poles in condensed matter systems}, journal = {Phys. Rev. Res.}, volume = {2}, number = {2}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {jun}, abstract = {The existence or not of Landau poles is one of the oldest open questions in nonasymptotic quantum field theories. We investigate the Landau pole issue in two condensed matter systems whose long-wavelength physics is described by appropriate quantum field theories: the critical quantum magnet and Dirac fermions in graphene with long-range Coulomb interactions. The critical quantum magnet provides a classic example of a quantum phase transition, and it is well described by the phi(4) theory. We find that the irrelevant but symmetry-allowed couplings, such as the phi(6) potential, can significantly change the fate of the Landau pole in the emergent phi(4) theory. We obtain the coupled beta functions of a phi(4) + phi(6) potential at both small and large orders. Already from the one-loop calculation, the Landau pole is replaced by an ultraviolet fixed point. A Lipatov analysis at large orders reveals that the inclusion of a phi(6) term also has important repercussions for the high-order expansion of the beta functions. We also investigate the role of the Landau pole in a very different system: Dirac fermions in 2 + 1 dimensions with long-range Coulomb interactions, e.g., graphene. Both the weak-coupling perturbation theory up to two loops and a low-order large-N calculation show the absence of a Landau pole. Furthermore, we calculate the asymptotic expansion coefficients of the beta function. We find that the asymptotic coefficient is bounded by that of a pure bosonic phi(4) theory, and consequently graphene is free from Landau poles if the pure (4) theory does not manifest a Landau pole. We briefly discuss possible experiments that could potentially probe the existence of a Landau pole in these systems. Studying Landau poles in suitable condensed matter systems is of considerable fundamental importance since the relevant Landau pole energy scales in particle physics, whether it is quantum electrodynamics or Higgs physics, are completely unattainable.}, doi = {10.1103/PhysRevResearch.2.023310}, author = {Jian, Shao-Kai and Barnes, Edwin and Das Sarma, Sankar} } @article {tsai_learning_2020, title = {Learning molecular dynamics with simple language model built upon long short-term memory neural network}, journal = {Nat. Commun.}, volume = {11}, number = {1}, year = {2020}, note = {Place: HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY Publisher: NATURE RESEARCH Type: Article}, month = {oct}, abstract = {Recurrent neural networks have led to breakthroughs in natural language processing and speech recognition. Here we show that recurrent networks, specifically long short-term memory networks can also capture the temporal evolution of chemical/biophysical trajectories. Our character-level language model learns a probabilistic model of 1-dimensional stochastic trajectories generated from higher-dimensional dynamics. The model captures Boltzmann statistics and also reproduces kinetics across a spectrum of timescales. We demonstrate how training the long short-term memory network is equivalent to learning a path entropy, and that its embedding layer, instead of representing contextual meaning of characters, here exhibits a nontrivial connectivity between different metastable states in the underlying physical system. We demonstrate our model{\textquoteright}s reliability through different benchmark systems and a force spectroscopy trajectory for multi-state riboswitch. We anticipate that our work represents a stepping stone in the understanding and use of recurrent neural networks for understanding the dynamics of complex stochastic molecular systems. Artificial neural networks have been successfully used for language recognition. Tsai et al. use the same techniques to link between language processing and prediction of molecular trajectories and show capability to predict complex thermodynamics and kinetics arising in chemical or biological physics.}, issn = {2041-1723}, doi = {10.1038/s41467-020-18959-8}, author = {Tsai, Sun-Ting and Kuo, En-Jui and Tiwary, Pratyush} } @article {kollar_line-graph_2020, title = {Line-{Graph} {Lattices}: {Euclidean} and {Non}-{Euclidean} {Flat} {Bands}, and {Implementations} in {Circuit} {Quantum} {Electrodynamics}}, journal = {Commun. Math. Phys.}, volume = {376}, number = {3}, year = {2020}, note = {Place: ONE NEW YORK PLAZA, SUITE 4600, NEW YORK, NY, UNITED STATES Publisher: SPRINGER Type: Article}, month = {jun}, pages = {1909{\textendash}1956}, abstract = {Materials science and the study of the electronic properties of solids are a major field of interest in both physics and engineering. The starting point for all such calculations is single-electron, or non-interacting, band structure calculations, and in the limit of strong on-site confinement this can be reduced to graph-like tight-binding models. In this context, both mathematicians and physicists have developed largely independent methods for solving these models. In this paper we will combine and present results from both fields. In particular, we will discuss a class of lattices which can be realized as line graphs of other lattices, both in Euclidean and hyperbolic space. These lattices display highly unusual features including flat bands and localized eigenstates of compact support. We will use the methods of both fields to show how these properties arise and systems for classifying the phenomenology of these lattices, as well as criteria for maximizing the gaps. Furthermore, we will present a particular hardware implementation using superconducting coplanar waveguide resonators that can realize a wide variety of these lattices in both non-interacting and interacting form.

}, issn = {0010-3616}, doi = {10.1007/s00220-019-03645-8}, author = {Kollar, Alicia J. and Fitzpatrick, Mattias and Sarnak, Peter and Houck, Andrew A.} } @conference {mazurek_loophole-free_2020, title = {Loophole-{Free} {Test} of {Einstein}-{Podolsky}-{Rosen} {Steering} with {One} {Bit} of {Faster}-than-{Light} {Communication}}, booktitle = {Conference on Lasers and Electro-Optics (CLEO)}, series = {Conference on {Lasers} and {Electro}-{Optics}}, year = {2020}, note = {Backup Publisher: IEEE ISSN: 2160-9020 Type: Proceedings Paper}, publisher = {IEEE}, organization = {IEEE}, abstract = {The communication cost for classically simulating Einstein-Podolsky-Rosen (EPR) steering correlations quantifies their strength. We report a loophole-free demonstration of EPR steering correlations requiring more than one faster-than-light bit to simulate. (C) 2020 The Author(s)

}, isbn = {978-1-943580-76-7}, author = {Mazurek, M. D. and Xiang, Y. and Stevens, M. J. and Bienfang, J. C. and Wayne, M. A. and Abellan, C. and Amaya, W. and Mitchell, M. W. and Mirin, R. P. and Nam, S. W. and He, Q. and Shalm, L. K. and Wiseman, H. M.} } @article { ISI:000527491100005, title = {Magic wavelength of the Ba-138(+) 6s S-2(1/2)-5d D-2(5/2) clock transition}, journal = {Phys. Rev. A}, volume = {101}, number = {4}, year = {2020}, month = {APR 22}, pages = {042507}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The zero crossing of the dynamic differential scalar polarizability of the S-1/2 - D-5/2 clock transition in Ba-138(+) has been determined to be 459.1614(28) THz. Together with previously determined matrix elements and branching ratios, this tightly constrains the dynamic differential scalar polarizability of the clock transition over a large wavelength range (greater than or similar to 700 nm). In particular, it allows an estimate of the blackbody radiation shift of the clock transition at room temperature.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.101.042507}, author = {Chanu, S. R. and Koh, V. P. W. and Arnold, K. J. and Kaewuam, R. and Tan, T. R. and Zhang, Zhiqiang and Safronova, M. S. and Barrett, M. D.} } @article {zheng_magic_2020, title = {Magic wavelengths of the {Yb} (6s(2) {S}-1(0)-6s6p {P}-3(1)) intercombination transition}, journal = {Phys. Rev. A}, volume = {102}, number = {6}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {dec}, abstract = {We calculate and measure the magic wavelengths for the 6s(2) S-1(0)-6s6p P-3(1) intercombination transition of the neutral ytterbium atom. The calculation is performed with the ab initio configuration interaction + all-order method. The measurement is done with laser spectroscopy on cold atoms in an optical dipole trap. The magic wavelengths are determined to be 1035.68(4) nm for the pi transition (Delta m = 0) and 1036.12(3) nm for the sigma transitions (vertical bar Delta m vertical bar = 1) in agreement with the calculated values. Laser cooling on the narrow intercombination transition could achieve better results for atoms in an optical dipole trap when the trap wavelength is tuned to near the magic wavelength.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.102.062805}, author = {Zheng, T. A. and Yang, Y. A. and Safronova, M. S. and Safronova, I, U. and Xiong, Zhuan-Xian and Xia, T. and Lu, Z-T} } @article { ISI:000575114800001, title = {Magic-angle semimetals}, journal = {npj Quantum Mater.}, volume = {5}, number = {1}, year = {2020}, month = {OCT 6}, pages = {71}, publisher = {NATURE RESEARCH}, type = {Article}, abstract = {Breakthroughs in two-dimensional van der Waals heterostructures have revealed that twisting creates a moire pattern that quenches the kinetic energy of electrons, allowing for exotic many-body states. We show that cold atomic, trapped ion, and metamaterial systems can emulate the effects of a twist in many models from one to three dimensions. Further, we demonstrate at larger angles (and argue at smaller angles) that by considering incommensurate effects, the magic-angle effect becomes a single-particle quantum phase transition (including in a model for twisted bilayer graphene in the chiral limit). We call these models {\textquoteleft}{\textquoteleft}magic-angle semimetals{{\textquoteright}{\textquoteright}}. Each contains nodes in the band structure and an incommensurate modulation. At magic-angle criticality, we report a nonanalytic density of states, flat bands, multifractal wave functions that Anderson delocalize in momentum space, and an essentially divergent effective interaction scale. As a particular example, we discuss how to observe this effect in an ultracold Fermi gas.}, doi = {10.1038/s41535-020-00271-9}, author = {Fu, Yixing and Konig, Elio J. and Wilson, Justin H. and Chou, Yang-Zhi and Pixley, Jedediah H.} } @article {chou_magic-angle_2020, title = {Magic-angle semimetals with chiral symmetry}, journal = {Phys. Rev. B}, volume = {101}, number = {23}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {jun}, abstract = {We construct and solve a two-dimensional, chirally symmetric model of Dirac cones subjected to a quasiperiodic modulation. In real space, this is realized with a quasiperiodic hopping term. This hopping model, as we show, at the Dirac node energy has a rich phase diagram with a semimetal-to-metal phase transition at intermediate amplitude of the quasiperiodic modulation, and a transition to a phase with a diverging density of states (DOS) and subdiffusive transport when the quasiperiodic hopping is strongest. We further demonstrate that the semimetal-to-metal phase transition can be characterized by the multifractal structure of eigenstates in momentum space and can be considered as a unique {\textquotedblleft}unfreezing{\textquotedblright} transition. This unfreezing transition in momentum space generates flat bands with a dramatically renormalized bandwidth in the metallic phase similar to the phenomena of the band structure of twisted bilayer graphene at the magic angle. We characterize the nature of this transition numerically as well as analytically in terms of the formation of a band of topological zero modes. For pure quasiperiodic hopping, we provide strong numerical evidence that the low-energy DOS develops a divergence and the eigenstates exhibit Chalker (quantum-critical) scaling despite the model not being random. At particular commensurate limits the model realizes higher-order topological insulating phases. We discuss how these systems can be realized in experiments on ultracold atoms and metamaterials.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.101.235121}, author = {Chou, Yang-Zhi and Fu, Yixing and Wilson, Justin H. and Konig, E. J. and Pixley, J. H.} } @article { ISI:000544124500044, title = {Magnet System for the Quantum Electromechanical Metrology Suite}, journal = {IEEE Trans. Instrum. Meas.}, volume = {69}, number = {8}, year = {2020}, month = {AUG.}, pages = {5736-5744}, publisher = {IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC}, type = {Article}, abstract = {The design of the permanent magnet system for the new quantum electromechanical metrology suite (QEMMS) is described. The QEMMS, developed at the National Institute of Standards and Technology (NIST), consists of a Kibble balance, a programmable Josephson voltage standard, and a quantum Hall resistance standard. It will be used to measure masses up to 100 g with relative uncertainties below 2 x 10(-8). The magnet system is based on the design of the NIST-4 magnet system with significant changes to adopt to a smaller Kibble balance and to overcome known practical limitations. Analytical models are provided to describe the coil-current effect and model the forces required to split the magnet into two parts to install the coil. Both models are compared to simulation results obtained with finite-element analysis and measurement results. Other aspects such as the coil design and flatness of Bl profile are considered.}, keywords = {Air gaps, Force, Kibble balance, magnet circuit, magnet system, Magnetic circuits, Magnetic noise, Magnetic shielding, mass measurement, Permanent magnets, Superconducting magnets}, issn = {0018-9456}, doi = {10.1109/TIM.2019.2959852}, author = {Marangoni, Rafael R. and Haddad, Darine and Seifert, Frank and Chao, Leon S. and Newell, David B. and Schlamminger, Stephan} } @article {masson_many-body_2020, title = {Many-{Body} {Signatures} of {Collective} {Decay} in {Atomic} {Chains}}, journal = {Phys. Rev. Lett.}, volume = {125}, number = {26}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, abstract = {Fully inverted atoms placed at exactly the same location synchronize as they deexcite, and light is emitted in a burst (known as {\textquotedblleft}Dicke{\textquoteright}s superradiance{\textquotedblright}). We investigate the role of (mite interatomic separation on correlated decay in mesoscopic chains and provide an understanding in terms of collective jump operators. We show that the superradiant burst survives at small distances, despite Hamiltonian dipole-dipole interactions. However, for larger separations, competition between different jump operators leads to dephasing, suppressing superradiance. Collective effects are still significant for arrays with lattice constants of the order of a wavelength, and lead to a photon emission rate that decays nonexponentially in time. We calculate the two-photon correlation function and demonstrate that emission is correlated and directional, as well as sensitive to small changes in the interatomic distance. These features can be measured in current experimental setups, and are robust to realistic imperfections.

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.125.263601}, author = {Masson, Stuart J. and Ferrier-Barbut, Igor and Orozco, Luis A. and Browaeys, Antoine and Asenjo-Garcia, Ana} } @article { ISI:000570982600002, title = {Many-Body Dephasing in a Trapped-Ion Quantum Simulator}, journal = {Phys. Rev. Lett.}, volume = {125}, number = {12}, year = {2020}, month = {SEP 18}, pages = {120605}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {How a closed interacting quantum many-body system relaxes and dephases as a function of time is a fundamental question in thermodynamic and statistical physics. In this Letter, we analyze and observe the persistent temporal fluctuations after a quantum quench of a tunable long-range interacting transverse-field Ising Hamiltonian realized with a trapped-ion quantum simulator. We measure the temporal fluctuations in the average magnetization of a finite-size system of spin-1/2 particles. We experiment in a regime where the properties of the system are closely related to the integrable Hamiltonian with global spin-spin coupling, which enables analytical predictions for the long-time nonintegrable dynamics. The analytical expression for the temporal fluctuations predicts the exponential suppression of temporal fluctuations with increasing system size. Our measurement data is consistent with our theory predicting the regime of many-body dephasing.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.125.120605}, author = {Kaplan, Harvey B. and Guo, Lingzhen and Tan, Wen Lin and De, Arinjoy and Marquardt, Florian and Pagano, Guido and Monroe, Christopher} } @article {16686, title = {Many-Body Dynamical Localization in a Kicked Lieb-Liniger Gas}, journal = {Phys. Rev. Lett.}, volume = {124}, year = {2020}, month = {04/2020}, pages = {155302}, abstract = {The kicked rotor system is a textbook example of how classical and quantum dynamics can drastically differ. The energy of a classical particle confined to a ring and kicked periodically will increase linearly in time whereas in the quantum version the energy saturates after a finite number of kicks. The quantum system undergoes Anderson localization in angular-momentum space. Conventional wisdom says that in a many-particle system with short-range interactions the localization will be destroyed due to the coupling of widely separated momentum states. Here we provide evidence that for an interacting one-dimensional Bose gas, the Lieb-Liniger model, the dynamical localization can persist at least for an unexpectedly long time.

}, keywords = {Quantum Physics, Thermodynamics}, doi = {10.1103/PhysRevLett.124.155302}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.124.155302}, author = {Rylands, Colin and Rozenbaum, Efim B. and Galitski, Victor and Konik, Robert} } @article {19051, title = {Many-Body Level Statistics of Single-Particle Quantum Chaos}, journal = {Phys. Rev. Lett.}, volume = {125}, year = {2020}, month = {Dec}, pages = {250601}, doi = {10.1103/PhysRevLett.125.250601}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.125.250601}, author = {Liao, Yunxiang and Vikram, Amit and Galitski, Victor} } @article { ISI:000505981500001, title = {Many-body localization landscape}, journal = {Phys. Rev. B}, volume = {101}, number = {1}, year = {2020}, month = {JAN 6}, pages = {014201}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We generalize the notion of {\textquoteleft}{\textquoteleft}localization landscape,{{\textquoteright}{\textquoteright}} introduced by M. Filoche and S. Mayboroda {[}Proc. Natl. Acad. Sci. USA 109, 14761 (2012)] for the single-particle Schrodinger operator, to a wide class of interacting many-body Hamiltonians. The many-body localization landscape (MBLL) is defined on a graph in the Fock space, whose nodes represent the basis vectors in the Fock space and edges correspond to transitions between the nodes connected by the hopping term in the Hamiltonian. It is shown that in analogy to the single-particle case, the inverse MBLL plays the role of an effective potential in the Fock space. We construct a generalized discrete Agmon metric and prove Agmon inequalities on the Fock-state graph to obtain bounds on the exponential decay of the many-body wave functions in the Fock space. The corresponding construction is motivated by the semiclassical WKB approximation, but the bounds are exact and fully quantum mechanical. We then prove a series of locality theorems which establish where in the Fock space we expect eigenstates to localize. Using these results as well as the locator expansion, we establish evidence for the existence of many-body localized states for a wide class of lattice models in any physical dimension in at least a part of their Hilbert space. The key to this argument is the observation that in sharp contrast to the conventional locator expansion for the Green{\textquoteright}s function, the locator expansion for the landscape function contains no resonances. For short-range hopping, which limits the connectivity of the Fock-state graph, the locator series is proven to be convergent and bounded by a simple geometric series. This, in combination with the discrete Agmon-type inequalities and the locality theorems, shows that localization for a fraction of the Hilbert space survives weak interactions and weak hopping at least for some realizations of disorder, but cannot prove or rule out localization of the entire Hilbert space. We qualitatively discuss potential breakdown of the locator expansion in the MBLL for long-range hopping and the appearance of a mobility edge in higher-dimensional theories.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.101.014201}, author = {Balasubramanian, Shankar and Liao, Yunxiang and Galitski, Victor} } @article {16666, title = {Many-body topological invariants from randomized measurements in synthetic quantum matter}, journal = {Science Advances}, volume = {6}, year = {2020}, abstract = {Many-body topological invariants, as quantized highly nonlocal correlators of the many-body wave function, are at the heart of the theoretical description of many-body topological quantum phases, including symmetry-protected and symmetry-enriched topological phases. Here, we propose and analyze a universal toolbox of measurement protocols to reveal many-body topological invariants of phases with global symmetries, which can be implemented in state-of-the-art experiments with synthetic quantum systems, such as Rydberg atoms, trapped ions, and superconducting circuits. The protocol is based on extracting the many-body topological invariants from statistical correlations of randomized measurements, implemented with local random unitary operations followed by site-resolved projective measurements. We illustrate the technique and its application in the context of the complete classification of bosonic symmetry-protected topological phases in one dimension, considering in particular the extended Su-Schrieffer-Heeger spin model, as realized with Rydberg tweezer arrays.

}, doi = {10.1126/sciadv.aaz3666}, url = {https://advances.sciencemag.org/content/6/15/eaaz3666}, author = {Elben, Andreas and Yu, Jinlong and Zhu, Guanyu and Hafezi, Mohammad and Pollmann, Frank and Zoller, Peter and Vermersch, Beno\^{\i}t} } @article {clayburn_measurement_2020, title = {Measurement of the molecular dipole moment and the hyperfine and {Lambda}-doublet splittings of the {B}-3 {Pi}(1) state of thallium fluoride}, journal = {Phys. Rev. A}, volume = {102}, number = {5}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {nov}, abstract = {We report high-precision measurements on the thallium fluoride (J) over tilde = 1 hyperfine manifold of the B-3 Pi(1) (v = 0) state. This state is of special interest because it is central to an optical cycling scheme that is envisioned to play an important role in enhancing the sensitivity of the CeNTREX nuclear Schiff-moment experiment presently under construction. The measurements are made by monitoring the fluorescence induced by narrow-band laser excitation of a cryogenic molecular beam. We use a multipass arrangement of the laser beam to enhance fluorescence. When viewed with a camera, we can spatially resolve images from adjacent passes that approach the molecules from opposing directions. These images yield a sensitive visual method to identify the central frequency of a transition. Coupling these line-center determinations with frequency calibration from an acousto-optic modulator has allowed a more precise determination of the (J) over tilde = 1 manifold of hyperfine level splittings. We observe Stark shifts of the (J) over tilde = 1 levels and infer a permanent electric dipole moment of 2.28(7) D and Lambda-doublet splittings for the F-1{\textquoteright} = 1/2 and F-1{\textquoteright} = 3/2 manifolds of 14.4(9) and 17.4(11) MHz, respectively.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.102.052802}, author = {Clayburn, N. B. and Wright, T. H. and Norrgard, E. B. and DeMille, D. and Hunter, L. R.} } @conference {muller_measuring_2020, title = {Measuring the dark exciton in a quantum dot inside a planar microcavity using a bright state cycling transition}, booktitle = {Conference on Lasers and Electro-Optics (CLEO)}, series = {Conference on {Lasers} and {Electro}-{Optics}}, year = {2020}, note = {Backup Publisher: IEEE ISSN: 2160-9020 Type: Proceedings Paper}, publisher = {IEEE}, organization = {IEEE}, abstract = {We demonstrate the resonant excitation of a so-called dark exciton state in a quantum dot with a readout scheme based on the resonance fluorescence of the correlated bright exciton. (C) 2020 The Author(s)

}, isbn = {978-1-943580-76-7}, author = {Muller, Markus and Cao, Bin and Solomon, Glenn S.} } @article {wu_microwave{\textendash}optical_2020, title = {Microwave-to-{Optical} {Transduction} {Using} a {Mechanical} {Supermode} for {Coupling} {Piezoelectric} and {Optomechanical} {Resonators}}, journal = {Phys. Rev. Appl.}, volume = {13}, number = {1}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {jan}, abstract = {The successes of superconducting quantum circuits at local manipulation of quantum information and photonics technology at long-distance transmission of the same have spurred interest in the development of quantum transducers for efficient, low-noise, and bidirectional frequency conversion of photons between the microwave and optical domains. We propose to realize such functionality through the coupling of electrical, piezoelectric, and optomechanical resonators. The coupling of the mechanical subsystems enables formation of a resonant mechanical supermode that provides a mechanically mediated, efficient single interface to both the microwave and optical domains. The conversion process is analyzed by applying an equivalent circuit model that relates device-level parameters to overall figures of merit for conversion efficiency eta and added noise N. These can be further enhanced by proper impedance matching of the transducer to an input microwave transmission line. The performance of potential transducers is assessed through finite-element simulations, with a focus on geometries in GaAs, followed by considerations of the AlN, LiNbO3, and AlN-on-Si platforms. We present strategies for maximizing eta and minimizing N, and find that simultaneously achieving eta {\textgreater} 50\% and N {\textless} 0.5 should be possible with current technology. We find that the use of a mechanical supermode for mediating transduction is a key enabler for high-efficiency operation, particularly when paired with an appropriate microwave impedance-matching network. Our comprehensive analysis of the full transduction chain enables us to outline a development path for the realization of high-performance quantum transducers that will constitute a valuable resource for quantum information science.

}, issn = {2331-7019}, doi = {10.1103/PhysRevApplied.13.014027}, author = {Wu, Marcelo and Zeuthen, Emil and Balram, Krishna Coimbatore and Srinivasan, Kartik} } @article { ISI:000571399800001, title = {Minimal Model for Fast Scrambling}, journal = {Phys. Rev. Lett.}, volume = {125}, number = {13}, year = {2020}, month = {SEP 21}, pages = {130601}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study quantum information scrambling in spin models with both long-range all-to-all and shortrange interactions. WC argue that a simple global, spatially homogeneous interaction together with local chaotic dynamics is sufficient to give rise to fast scrambling, which describes the spread of quantum information over the entire system in a time that is logarithmic in the system size. This is illustrated in two tractable models: (1) a random circuit with Haar random local unitaties and a global interaction and (2) a classical model of globally coupled nonlinear oscillators. We use exact numerics to provide further evidence by studying the time evolution of an out-of-time-order correlator and entanglement entropy in spin chains of intermediate sizes. Our results pave the way towards experimental investigations of fast scrambling and aspects of quantum gravity with quantum simulators.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.125.130601}, author = {Belyansky, Ron and Bienias, Przemyslaw and Kharkov, Yaroslav A. and Gorshkov, V, Alexey and Swingle, Brian} } @article { ISI:000512770000004, title = {Mobility edge and intermediate phase in one-dimensional incommensurate lattice potentials}, journal = {Phys. Rev. B}, volume = {101}, number = {6}, year = {2020}, month = {FEB 11}, pages = {064203}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study theoretically the localization properties of two distinct one-dimensional quasiperiodic lattice models with a single-particle mobility edge (SPME) separating extended and localized states in the energy spectrum. The first one is the familiar Soukoulis-Economou trichromatic potential model with two incommensurate potentials, and the second is a system consisting of two coupled 1D Aubry-Andre chains each containing one incommensurate potential. We show that as a function of the Hamiltonian model parameters, both models have a wide single-particle intermediate phase, defined as the regime where localized and extended single-particle states coexist in the spectrum, leading to a behavior intermediate between purely extended or purely localized when the system is dynamically quenched from a generic initial state. Our results thus suggest that both systems could serve as interesting experimental platforms for studying the interplay between localized and extended states, and may provide insight into the role of the coupling of small baths to localized systems. We also calculate the Lyapunov (or localization) exponent for several incommensurate 1D models exhibiting SPME, finding that such localization critical exponents for quasiperiodic potential induced localization are nonuniversal and depend on the microscopic details of the Hamiltonian.

}, issn = {2469-9950}, doi = {10.1103/PhysRevB.101.064203}, author = {Li, Xiao and Das Sarma, Sankar} } @article { ISI:000523412800006, title = {Mobius Insulator and Higher-Order Topology in MnBi2nTe3n+1}, journal = {Phys. Rev. Lett.}, volume = {124}, number = {13}, year = {2020}, month = {APR 3}, pages = {136407}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We propose MnBi2nTe3n+1 as a magnetically tunable platform for realizing various symmetry-protected higher-order topology. Its canted antiferromagnetic phase can host exotic topological surface states with a Mobius twist that are protected by nonsymmorphic symmetry. Moreover, opposite surfaces hosting Mobius fermions are connected by one-dimensional chiral hinge modes, which offers the first material candidate of a higher-order topological Mobius insulator. We uncover a general mechanism to feasibly induce this exotic physics by applying a small in-plane magnetic field to the antiferromagnetic topological insulating phase of MnBi2nTe3n+1, as well as other proposed axion insulators. For other magnetic configurations, two classes of inversion-protected higher-order topological phases are ubiquitous in this system, which both manifest gapped surfaces and gapless chiral hinge modes. We systematically discuss their classification, microscopic mechanisms, and experimental signatures. Remarkably, the magnetic-field-induced transition between distinct chiral hinge mode configurations provides an effective {\textquoteleft}{\textquoteleft}topological magnetic switch{{\textquoteright}{\textquoteright}}.

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.124.136407}, author = {Zhang, Rui-Xing and Wu, Fengcheng and Das Sarma, Sankar} } @article { ISI:000565086500001, title = {Multiterminal Josephson Effect}, journal = {Phys. Rev. X}, volume = {10}, number = {3}, year = {2020}, month = {SEP 2}, pages = {031051}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We report a probable observation of the dc Josephson effect in mesoscopic junctions of three and four superconductors. The devices are fabricated in a top-down fashion from a hybrid semiconductor-superconductor InAs/Al epitaxial heterostructure. In general, the critical current of an N-terminal junction is an (N - 1)-dimensional hypersurface in the space of bias currents, which can be reduced to a set of critical current contours. The geometry of critical current contours exhibits nontrivial responses to electrical gating, magnetic field, and phase bias, and it can be reproduced by the scattering formulation of the Josephson effect generalized to the case of N > 2. Besides establishing solid ground beneath a host of recent theory proposals, our experiment accomplishes an important step toward creating trijunctions of topological superconductors, essential for braiding operations.}, issn = {2160-3308}, doi = {10.1103/PhysRevX.10.031051}, author = {Pankratova, Natalia and Lee, Hanho and Kuzmin, Roman and Wickramasinghe, Kaushini and Mayer, William and Yuan, Joseph and Vavilov, Maxim G. and Shabani, Javad and Manucharyan, Vladimir E.} } @article { ISI:000575175400005, title = {Nature of the nonequilibrium phase transition in the non-Markovian driven Dicke model}, journal = {Phys. Rev. A}, volume = {102}, number = {3}, year = {2020}, month = {SEP 23}, pages = {032218}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The Dicke model famously exhibits a phase transition to a superradiant phase with a macroscopic population of photons and is realized in multiple settings in open quantum systems. In this paper, we study a variant of the Dicke model where the cavity mode is lossy due to the coupling to a Markovian environment while the atomic mode is coupled to a colored bath. We analytically investigate this model by inspecting its low-frequency behavior via the Schwinger-Keldysh field theory and carefully examine the nature of the corresponding superradiant phase transition. Integrating out the fast modes, we can identify a simple effective theory allowing us to derive analytical expressions for various critical exponents including the dynamical exponent. We find excellent agreement with previous numerical results when the non-Markovian bath is at zero temperature; however, contrary to these studies, our low-frequency approach reveals that the same exponents govern the critical behavior when the colored bath is at finite temperature unless the chemical potential is zero. Furthermore, we show that the superradiant phase transition is classical in nature, while it is genuinely nonequilibrium. We derive a fractional Langevin equation and conjecture the associated fractional Fokker-Planck equation that captures the system{\textquoteright}s long-time memory as well as its nonequilibrium behavior. Finally, we consider finite-size effects at the phase transition and identify the finite-size scaling exponents, unlocking a rich behavior in both statics and dynamics of the photonic and atomic observables.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.102.032218}, author = {Lundgren, Rex and Gorshkov, V, Alexey and Maghrebi, Mohammad F.} } @article {flebus_non-hermitian_2020, title = {Non-{Hermitian} topology of one-dimensional spin-torque oscillator arrays}, journal = {Phys. Rev. B}, volume = {102}, number = {18}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {nov}, abstract = {Magnetic systems have been extensively studied from both a fundamental physics perspective and as technological building blocks. The topological properties of magnonic excitations in these systems remain relatively unexplored, due to their inherently dissipative nature. The recent extension of the theory of topological classification to non-Hermitian Hamiltonians provides a pathway to engineer topological phases in dissipative systems. Here, we propose a magnonic realization of a topological, non-Hermitian system. A crucial ingredient of our proposal is the injection of spin current into the magnetic system, which alters and can even change the sign of terms describing dissipation. We show that the magnetic dynamics of an array of spin-torque oscillators can be mapped onto a non-Hermitian Su-Schrieffer-Heeger model exhibiting topologically protected edge states. The nontrivial topological phase is accessed by tuning the spin current injected into the array. We derive this result using both exact diagonalization of the effective non-Hermitian Hamiltonian and numerical analysis of the nonlinear equations of motion. In the nontrivial topological phase, a single spin-torque oscillator on the edge of the array is driven into auto-oscillation and emits a microwave signal, while the bulk oscillators remain inactive. Our findings have practical utility for memory devices and spintronics neural networks relying on spin-torque oscillators as constituent units.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.180408}, author = {Flebus, Benedetta and Duine, Rembert A. and Hurst, Hilary M.} } @article {sinha_non-markovian_2020, title = {Non-{Markovian} {Collective} {Emission} from {Macroscopically} {Separated} {Emitters}}, journal = {Phys. Rev. Lett.}, volume = {124}, number = {4}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {jan}, abstract = {We study the collective radiative decay of a system of two two-level emitters coupled to a one-dimensional waveguide in a regime where their separation is comparable to the coherence length of a spontaneously emitted photon. The electromagnetic field propagating in the cavity-like geometry formed by the emitters exerts a retarded backaction on the system leading to strongly non-Markovian dynamics. The collective spontaneous emission rate of the emitters exhibits an enhancement or inhibition beyond the usual Dicke superradiance and subradiance due to self-consistent coherent time-delayed feedback.

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.124.043603}, author = {Sinha, Kanupriya and Meystre, Pierre and Goldschmidt, Elizabeth A. and Fatemi, Fredrik K. and Rolston, S. L. and Solano, Pablo} } @inbook {rylands_nonequilibrium_2020, title = {Nonequilibrium {Aspects} of {Integrable} {Models}}, booktitle = {Annual Review of Condensed Matter Physics}, series = {Annual {Review} of {Condensed} {Matter} {Physics}}, volume = {11}, year = {2020}, note = {ISSN: 1947-5454 Journal Abbreviation: Annu. Rev. Condens. Matter Phys. Type: Review; Book Chapter}, pages = {147{\textendash}168}, publisher = {ANNUAL REVIEWS}, organization = {ANNUAL REVIEWS}, abstract = {Driven by breakthroughs in experimental and theoretical techniques, the study of nonequilibrium quantum physics is a rapidly expanding field with many exciting new developments. Among themanifold ways the topic can be investigated, one-dimensional systems provide a particularly fine platform. The trifecta of strongly correlated physics, powerful theoretical techniques, and experimental viability have resulted in a flurry of research activity over the past decade or so. In this review, we explore the nonequilibrium aspects of one-dimensional systems that are integrable. Through a number of illustrative examples, we discuss nonequilibrium phenomena that arise in such models, the role played by integrability, and the consequences these have for more generic systems.

}, keywords = {integrability, quantum work, quench dynamics, RG flow in time}, doi = {10.1146/annurev-conmatphys-031119-050630}, author = {Rylands, Colin and Andrei, Natan}, editor = {Marchetti, MC and Mackenzie, AP} } @article { ISI:000550580800001, title = {Nonequilibrium Criticality in Quench Dynamics of Long-Range Spin Models}, journal = {Phys. Rev. Lett.}, volume = {125}, number = {4}, year = {2020}, month = {JUL 21}, pages = {040602}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Long-range interacting spin systems are ubiquitous in physics and exhibit a variety of ground-state disorder-to-order phase transitions. We consider a prototype of infinite-range interacting models known as the Lipkin-Meshkov-Glick model describing the collective interaction of N spins and investigate the dynamical properties of fluctuations and correlations after a sudden quench of the Hamiltonian. Specifically, we focus on critical quenches, where the initial state and/or the postquench Hamiltonian are critical. Depending on the type of quench, we identify three distinct behaviors where both the short-time dynamics and the stationary state at long times are effectively thermal, quantum, and genuinely nonequilibrium, characterized by distinct universality classes and static and dynamical critical exponents. These behaviors can be identified by an infrared effective temperature that is finite, zero, and infinite (the latter scaling with the system size as N-1/3), respectively. The quench dynamics is studied through a combination of exact numerics and analytical calculations utilizing the nonequilibrium Keldysh field theory. Our results are amenable to realization in experiments with trapped-ion experiments where long-range interactions naturally arise.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.125.040602}, author = {Titum, Paraj and Maghrebi, Mohammad F.} } @article { ISI:000515062100001, title = {Nonequilibrium Fixed Points of Coupled Ising Models}, journal = {Phys. Rev. X}, volume = {10}, number = {1}, year = {2020}, month = {FEB 19}, pages = {011039}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Driven-dissipative systems are expected to give rise to nonequilibrium phenomena that are absent in their equilibrium counterparts. However, phase transitions in these systems generically exhibit an effectively classical equilibrium behavior in spite of their nonequilibrium origin. In this paper, we show that multicritical points in such systems lead to a rich and genuinely nonequilibrium behavior. Specifically, we investigate a driven-dissipative model of interacting bosons that possesses two distinct phase transitions: one from a high- to a low-density phase-reminiscent of a liquid-gas transition-and another to an antiferromagnetic phase. Each phase transition is described by the Ising universality class characterized by an (emergent or microscopic) Z(2) symmetry. However, they coalesce at a multicritical point, giving rise to a nonequilibrium model of coupled Ising-like order parameters described by a Z(2) x Z(2) symmetry. Using a dynamical renormalization-group approach, we show that a pair of nonequilibrium fixed points (NEFPs) emerge that govern the long-distance critical behavior of the system. We elucidate various exotic features of these NEFPs. In particular, we show that a generic continuous scale invariance at criticality is reduced to a discrete scale invariance. This further results in complex-valued critical exponents and spiraling phase boundaries, and it is also accompanied by a complex Liouvillian gap even close to the phase transition. As direct evidence of the nonequilibrium nature of the NEFPs, we show that the fluctuation-dissipation relation is violated at all scales, leading to an effective temperature that becomes {\textquoteleft}{\textquoteleft}hotter{{\textquoteright}{\textquoteright}} and {\textquoteleft}{\textquoteleft}hotter{{\textquoteright}{\textquoteright}} at longer and longer wavelengths. Finally, we argue that this nonequilibrium behavior can be observed in cavity arrays with cross-Kerr nonlinearities.}, keywords = {Photonics, Quantum Physics, Statistical Physics}, issn = {2160-3308}, doi = {10.1103/PhysRevX.10.011039}, author = {Young, Jeremy T. and Gorshkov, Alexey V. and Foss-Feig, Michael and Maghrebi, Mohammad F.} } @article { ISI:000506845000012, title = {Nonequilibrium nature of nonlinear optical response: Application to the bulk photovoltaic effect}, journal = {Phys. Rev. B}, volume = {101}, number = {4}, year = {2020}, month = {JAN 13}, pages = {045201}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The bulk photovoltaic effect is an example of a nonlinear optical response that leads to a DC current that is relevant for photovoltaic applications. In this paper, we theoretically study this effect in the presence of electron-phonon interactions. Using the response function formalism, we find that the nonlinear optical response, in general, contains three operator correlation functions, one of which is not ordered in time. This latter correlator cannot be computed from equilibrium field theory. Using a semiclassical approach instead, we show that the bulk photovoltaic effect can be attributed to the dipole moment of the generated excitons. We then confirm the validity of the semiclassical result (which agrees with the noninteracting result) for nonlinear DC response from a quantum master equation approach. From this formalism we find that, in contrast to usual linear response, the scattering rate has a strong implicit effect on the nonlinear DC response. Most interestingly, the semiclassical treatment shows that the nonlinear DC response for spatially inhomogeneous excitation profiles is strongly nonlocal and must involve the aforementioned out-of-time-ordered correlators that cannot be computed by equilibrium field theory.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.101.045201}, author = {Barik, Tamoghna and Sau, Jay D.} } @article {hsiang_nonequilibrium_2020, title = {Nonequilibrium nonlinear open quantum systems: {Functional} perturbative analysis of a weakly anharmonic oscillator}, journal = {Phys. Rev. D}, volume = {101}, number = {12}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {jun}, abstract = {We introduce a functional perturbative method for treating weakly nonlinear systems coupled with a quantum field bath. We demonstrate using this method to obtain the covariance matrix elements and the correlation functions of a quantum anharmonic oscillator interacting with a heat bath. We identify a fluctuation-dissipation relation based on the nonequilibrium dynamics of this nonlinear open quantum system. To establish its connection with dynamical equilibration, we further examine the energy flows between the anharmonic oscillator and the bath field. The vanishing of the net flow is an indication of the existence of an equilibrium state for such an open-system configuration. The results presented here are useful for studying the nonequilibrium physical processes of nonlinear quantum systems such as heat transfer or electron transport.}, issn = {1550-7998}, doi = {10.1103/PhysRevD.101.125002}, author = {Hsiang, Jen-Tsung and Hu, Bei-Lok} } @article {yang_nonequilibrium_2020, title = {Nonequilibrium steady state and heat transport in nonlinear open quantum systems: {Stochastic} influence action and functional perturbative analysis}, journal = {Ann. Phys.}, volume = {421}, year = {2020}, note = {Place: 525 B ST, STE 1900, SAN DIEGO, CA 92101-4495 USA Publisher: ACADEMIC PRESS INC ELSEVIER SCIENCE Type: Article}, month = {oct}, abstract = {In this paper, we show that a nonequilibrium steady state (NESS) exists at late times in open quantum systems with weak nonlinearity by following its nonequilibrium dynamics with a perturbative analysis. We consider an oscillator chain containing three-types of anharmonicity: cubic alpha- and quartic beta-type Fermi-Pasta-Ulam-Tsingou (FPUT) nearest-oscillator interactions and the on-site (pinned) Klein-Gordon (KG) quartic self-interaction. Assuming weak nonlinearity, we introduce a stochastic influence action approach to the problem and obtain the energy flows in different junctures across the chain. The formal results obtained here can be used for quantum transport problems in weakly nonlinear quantum systems. For alpha-type anharmonicity, we observe that the first-order corrections do not play any role in the thermal transport in the NESS of the configuration we considered. For KG and beta-types anharmonicity, we work out explicitly the case of two weakly nonlinearly coupled oscillators, with results scalable to any number of oscillators. We examine the late-time energy flows from one thermal bath to the other via the coupled oscillators, and show that both the zeroth- and the first-order contributions of the energy flows become constant in time at late times, signaling the existence of a late-time NESS to first order in nonlinearity. Our perturbative calculations provide a measure of the strength of nonlinearity for nonlinear open quantum systems, which may help control the mesoscopic heat transport distinct from or close to linear transport. Furthermore, our results also give a benchmark for the numerical challenge of simulating heat transport. Our setup and predictions can be implemented and verified by investigating heat flow in an array of Josephson junctions in the limit of large Josephson energy with the platform of circuit QED. (C) 2020 Elsevier Inc. All rights reserved.}, keywords = {Anharmonic chain, Feynman-Vernon influence functional, Functional perturbation, Nonequilibrium steady state, Open quantum systems, quantum transport}, issn = {0003-4916}, doi = {10.1016/j.aop.2020.168289}, author = {Yang, Jing and Hsiang, Jen-Tsung and Jordan, Andrew N. and Hu, B. L.} } @article {yoo_nonequilibrium_2020, title = {Nonequilibrium steady state phases of the interacting {Aubry}-{Andre}-{Harper} model}, journal = {Phys. Rev. B}, volume = {102}, number = {19}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {nov}, abstract = {Here, we study the phase diagram of the Aubry-Andre-Harper model in the presence of strong interactions as the strength of the quasiperiodic potential is varied. Previous work has established the existence of a many-body localized phase at a large potential strength; here, we find a rich phase diagram in the delocalized regime characterized by spin transport and unusual correlations. We calculate the nonequilibrium steady states of a boundary-driven strongly interacting Aubry-Andre-Harper model by employing the time-evolving block decimation algorithm on matrix product density operators. From these steady states, we extract spin transport as a function of system size and quasiperiodic potential strength. These data show spin transport going from superdiffusive to subdiffusive well before the localization transition; comparing to previous results, we also find that the transport transition is distinct from a transition observed in the speed of operator growth in the model. We also investigate the correlation structure of the steady state and find an unusual oscillation pattern for intermediate values of the potential strength. The unusual spin transport and quantum correlation structure suggest multiple dynamical phases between the much-studied thermal and many-body localized phases.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.195142}, author = {Yoo, Yongchan and Lee, Junhyun and Swingle, Brian} } @article {reiche_nonequilibrium_2020, title = {Nonequilibrium thermodynamics of quantum friction}, journal = {Phys. Rev. A}, volume = {102}, number = {5}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {nov}, abstract = {Thermodynamic principles are often deceptively simple and yet surprisingly powerful. We show how a simple rule, such as the net flow of energy in and out of a moving atom under a nonequilibrium steady state condition, can expose the shortcomings of many popular theories of quantum friction. Our thermodynamic approach provides a conceptual framework in guiding atom-optical experiments, thereby highlighting the importance of fluctuation-dissipation relations and long-time correlations between subsystems. Our results introduce consistency conditions for (numerical) models of nonequilibrium dynamics of open quantum systems.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.102.050203}, author = {Reiche, D. and Intravaia, F. and Hsiang, J-T and Busch, K. and Hu, B. L.} } @article { ISI:000510393100010, title = {Non-Markovian Collective Emission from Macroscopically Separated Emitters}, journal = {Phys. Rev. Lett.}, volume = {124}, number = {4}, year = {2020}, month = {JAN 31}, pages = {043603}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study the collective radiative decay of a system of two two-level emitters coupled to a one-dimensional waveguide in a regime where their separation is comparable to the coherence length of a spontaneously emitted photon. The electromagnetic field propagating in the cavity-like geometry formed by the emitters exerts a retarded backaction on the system leading to strongly non-Markovian dynamics. The collective spontaneous emission rate of the emitters exhibits an enhancement or inhibition beyond the usual Dicke superradiance and subradiance due to self-consistent coherent time-delayed feedback.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.124.043603}, author = {Sinha, Kanupriya and Meystre, Pierre and Goldschmidt, Elizabeth A. and Fatemi, Fredrik K. and Rolston, S. L. and Solano, Pablo} } @article { ISI:000517213700002, title = {Nonmonotonic plasmon dispersion in strongly interacting Coulomb Luttinger liquids}, journal = {Phys. Rev. B}, volume = {101}, number = {7}, year = {2020}, month = {FEB 27}, pages = {075430}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We demonstrate that the plasmon in one-dimensional Coulomb interacting electron fluids can develop a finite-momentum maxon-roton-like nonmonotonic energy-momentum dispersion. Such an unusual nonmonotonicity arises from the strongly interacting 1/r Coulomb potential going beyond the conventional band linearization approximation used in the standard bosonization theories of Luttinger liquids. We provide details for the nonmonotonic plasmon dispersion using both bosonization and random-phase approximation theories. We also calculate the specific heat including the nonmonotonicity and discuss possibilities for observing the nonmonotonic plasmon dispersion in various physical systems, including semiconductor quantum wires, carbon nanotubes, and the twisted bilayer graphene at subdegree twist angles, which naturally realize one-dimensional domain-wall states. We provide results for several different models of long-range interaction showing that the nonomonotonic charge collective mode dispersion is a generic phenomenon in one-dimensional strongly interacting electron systems.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.101.075430}, author = {Chou, Yang-Zhi and Das Sarma, Sankar} } @article {hao_nuclear_2020, title = {Nuclear spin-dependent parity-violating effects in light polyatomic molecules}, journal = {Phys. Rev. A}, volume = {102}, number = {5}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {nov}, abstract = {Measurements of nuclear spin-dependent parity-violating (NSD-PV) effects provide an excellent opportunity to test nuclear models and to search for physics beyond the Standard Model. Molecules possess closely spaced states with opposite parity which may be easily tuned to degeneracy to greatly enhance the observed parity-violating effects. A high-sensitivity measurement of NSD-PV effects using light triatomic molecules is in preparation [E. B. Norrgard et al., Common. Phys. 2, 77 (2019)]. Importantly, by comparing these measurements in light nuclei with prior and ongoing measurements in heavier systems, the contribution to NSD-PV from Z(0)-boson exchange between the electrons and the nuclei may be separated from the contribution of the nuclear anapole moment. Furthermore, light triatomic molecules offer the possibility to search for new particles, such as the postulated Z{\textquoteright} boson. In this work, we detail a sensitive measurement scheme and present high-accuracy molecular and nuclear calculations needed for interpretation of NSD-PV experiments on triatomic molecules composed of light elements, Be, Mg, N, and C. The ab initio nuclear structure calculations, performed within the no-core shell model provide a reliable prediction of the magnitude of different contributions to the NSD-PV effects in the four nuclei. These results differ significantly from the predictions of the standard single-particle model and highlight the importance of including many-body effects in such calculations. In order to extract the NSD-PV contributions from measurements, a parity-violating interaction parameter W-PV, which depends on the molecular structure, needs to be known with a high accuracy. We have calculated these parameters for the triatomic molecules of interest using the relativistic coupled-cluster approach. In order to facilitate the interpretation of future experiments we provide uncertainties on the calculated parameters. A scheme for measurement using laser-cooled polyatomic molecules in a molecular fountain is presented, along with an estimate of the expected sensitivity of such an experiment. This experimental scheme, combined with the presented state-of-the-art calculations, opens exciting prospects for a measurement of the anapole moment and the PV effects due to the electron-nucleon interactions with unprecedented accuracy and for a new path towards detection of signatures of physics beyond the Standard Model.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.102.052828}, author = {Hao, Yongliang and Navratil, Petr and Norrgard, Eric B. and Ilias, Miroslav and Eliav, Ephraim and Timmermans, Rob G. E. and Flambaum, Victor V. and Borschevsky, Anastasia} } @article { ISI:000524978500001, title = {Number-Theoretic Characterizations of Some Restricted Clifford}, journal = {Quantum}, volume = {4}, year = {2020}, month = {APR 3}, publisher = {VEREIN FORDERUNG OPEN ACCESS PUBLIZIERENS QUANTENWISSENSCHAF}, type = {Article}, abstract = {Kliuchnikov, Maslov, and Mosca proved in 2012 that a 2 x 2 unitary matrix V can be exactly represented by a single-qubit Clifford + T circuit if and only if the entries of V belong to the ring Z{[}1/root 2, i]. Later that year, Giles and Selinger showed that the same restriction applies to matrices that can be exactly represented by a multi-qubit Clifford + T circuit. These number-theoretic characterizations shed new light upon the structure of Clifford + T circuits and led to remarkable developments in the field of quantum compiling. In the present paper, we provide number-theoretic characterizations for certain restricted Clifford + T circuits by considering unitary matrices over subrings of Z{[}1/root 2, i]. We focus on the subrings Z{[}1./2], Z{[}1/root 2], Z{[}1/i root 2], and Z{[}1/2, i], and we prove that unitary matrices with entries in these rings correspond to circuits over well-known universal gate sets. In each case, the desired gate set is obtained by extending the set of classical reversible gates \{X, CX, CCX\} with an analogue of the Hadarnard gate and an optional phase gate.}, issn = {2521-327X}, author = {Amy, Matthew and Glaudell, Andrew N. and Ross, Neil J.} } @article {xie_observation_2020, title = {Observation of {Efimov} {Universality} across a {Nonuniversal} {Feshbach} {Resonance} in {K}-39}, journal = {Phys. Rev. Lett.}, volume = {125}, number = {24}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {dec}, abstract = {We study three-atom inelastic scattering in ultracold K-39 near a Feshbach resonance of intermediate coupling strength. The nonuniversal character of such resonance leads to an abnormally large Efimov absolute length scale and a relatively small effective range r(e), allowing the features of the 39 K Efimov spectrum to be better isolated from the short-range physics. Meticulous characterization of and correction for finite-temperature effects ensure high accuracy on the measurements of these features at large-magnitude scattering lengths. For a single Feshbach resonance, we unambiguously locate four distinct features in the Efimov structure. Three of these features form ratios that obey the Efimov universal scaling to within 10\%, while the fourth feature, occurring at a value of scattering length closest to r(e), instead deviates from the universal value.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.125.243401}, author = {Xie, Xin and Van de Graaff, Michael J. and Chapurin, Roman and Frye, Matthew D. and Hutson, Jeremy M. and D{\textquoteright}Incao, Jose P. and Julienne, Paul S. and Ye, Jun and Cornell, Eric A.} } @article {lu_-chip_2020, title = {On-chip optical parametric oscillation into the visible: generating red, orange, yellow, and green from a near-infrared pump}, journal = {Optica}, volume = {7}, number = {10}, year = {2020}, note = {Place: 2010 MASSACHUSETTS AVE NW, WASHINGTON, DC 20036 USA Publisher: OPTICAL SOC AMER Type: Article}, month = {oct}, pages = {1417{\textendash}1425}, abstract = {The on-chip generation of coherent, single-frequency laser light that can be tuned across the visible spectrum would help enable a variety of applications in spectroscopy, metrology, and quantum science. Recently, third-order optical parametric oscillation (OPO) in a microresonator has shown great promise as an efficient and scalable approach toward this end. However, considering visible light generation, so far only red light at {\textless}420 THz (near the edge of the visible band) has been reported. In this work, we overcome strong material dispersion at visible wavelengths and demonstrate on-chip OPO in a Si3N4 microresonator covering {\textgreater}130 THz of the visible spectrum, including red, orange, yellow, and green wavelengths. In particular, using an input pump laser that is scanned 5 THz in the near-infrared from 386 THz to 391 THz, the OPO output signal is tuned from the near-infrared at 395 THz to the visible at 528 THz, while the OPO output idler is tuned from the near-infrared at 378 THz to the infrared at 254 THz. The widest signal-idler separation of 274 THz is more than an octave in span and is the widest demonstrated for a nanophotonic OPO to date. More generally, our work shows how nonlinear nanophotonics can transform light from readily accessible compact near-infrared lasers to targeted visible wavelengths of interest. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement}, issn = {2334-2536}, doi = {10.1364/OPTICA.393810}, author = {Lu, Xiyuan and Moille, Gregory and Rao, Ashutosh and Westly, Daron A. and Srinivasan, Kartik} } @article { ISI:000550690300003, title = {On-demand indistinguishable single photons from an efficient and pure source based on a Rydberg ensemble}, journal = {Optica}, volume = {7}, number = {7}, year = {2020}, month = {JUL 20}, pages = {813-819}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {Single photons coupled to atomic systems have shown to be a promising platform for developing quantum technologies. Yet a bright on-demand, highly pure, and highly indistinguishable single-photon source compatible with atomic platforms is lacking. In this work, we demonstrate such a source based on a strongly interacting Rydberg system. The large optical nonlinearities in a blockaded Rydberg ensemble convert coherent light into a single collective excitation that can be coherently retrieved as a quantum field. We simultaneously observe a fully single-mode (spectral, temporal, spatial, and polarization) efficiency up to 0.098(2), a detector-background-subtracted g((2))+5.0(1.6) x 10(-4), and indistinguishability of 0.980(7), at an average photon production rate of 1.18(2) x 10(4) s(-1), All of these make this system promising for scalable quantum information applications. Furthermore, we investigate the effects of contaminant Rydberg excitations on the source efficiency and observed single-mode efficiencies up to 0.18(2) for lower photon rates. Finally, recognizing that many quantum information protocols require a single photon in a fully single mode, we introduce metrics that take into account all degrees of freedom to benchmark the performance of on-demand sources. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement}, issn = {2334-2536}, doi = {10.1364/OPTICA.391485}, author = {Ornelas-Huerta, D. P. and Craddock, A. N. and Goldschmidt, E. A. and Hachtel, A. J. and Wang, Y. and Bienias, P. and Gorshkov, A. V. and Rolston, S. L. and Porto, J. V.} } @article { ISI:000519701600004, title = {One-dimensional few-electron effective Wigner crystal in quantum and classical regimes}, journal = {Phys. Rev. B}, volume = {101}, number = {12}, year = {2020}, month = {MAR 16}, pages = {125113}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {A system of confined charged electrons interacting via the long-range Coulomb force can form a Wigner crystal due to their mutual repulsion. This happens when the potential energy of the system dominates over its kinetic energy, i.e., at low temperatures for a classical system and at low densities for a quantum one. At T = 0, the system is governed by quantum mechanics, and hence the spatial density peaks associated with crystalline charge localization are sharpened for a lower average density. Conversely, in the classical limit of high temperatures, the crystalline spatial density peaks are suppressed (recovered) at a lower (higher) average density. In this paper, we study those two limits separately using an exact diagonalization of small one-dimensional (1D) systems containing few (\<10) electrons and propose an approximate method to connect them into a unified effective phase diagram for Wigner few-electron crystallization. The result is a qualitative quantum-classical crossover phase diagram of an effective 1D Wigner crystal. We show that although such a 1D system is at best an effective crystal with no true long-range order (and thus no real phase transition), the spatial density peaks associated with the quasicrystallization should be experimentally observable in a few-electron 1D system. We find that the effective crystalline structure slowly disappears with both the crossover average density and crossover temperature for crystallization decreasing with increasing particle number, consistent with the absence of any true long-range 1D order. Thus, an effective few-electron 1D Wigner crystal may be construed either as existing at all densities (manifesting short-range order) or as nonexisting at all densities (not manifesting any long-range order). Within one unified description, we show through exact theoretical calculations how a small 1D system interacting through the long-range Coulomb interaction could manifest effective Wigner solid behavior both in classical and quantum regimes. In fact, one peculiar aspect of the effective finite-size nature of 1D Wigner crystallization we find is that even a short-range interaction would lead to a finite-size 1D crystal, except that the crystalline order vanishes much faster with increasing system size in the short-range interacting system compared with the long-range interacting one.

}, issn = {2469-9950}, doi = {10.1103/PhysRevB.101.125113}, author = {DinhDuy Vu and Das Sarma, Sankar} } @article {ge_operational_2020, title = {Operational resource theory of nonclassicality via quantum metrology}, journal = {Phys. Rev. Res.}, volume = {2}, number = {2}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, abstract = {The nonclassical properties of quantum states are of tremendous interest due to their potential applications in future technologies. It has recently been realized that the concept of a resource theory is a powerful approach to quantifying and understanding nonclassicality. To realize the potential of this approach, one must first find resource theoretic measures of nonclassicality that are operational, meaning that they also quantify the ability of quantum states to provide enhanced performance for specific tasks, such as precision sensing. Here we achieve a significant milestone in this endeavor by presenting such an operational resource theoretic measure. In addition to satisfying the requirements of a resource measure, it has the closest possible relationship to the quantum enhancement provided by a nonclassical state for measuring phase-space displacement: It is equal to this enhancement for pure states and has a tight upper bound on it for mixed states. We also show that a lower bound on this measure can be obtained experimentally using a simple Mach-Zehnder interferometer.}, doi = {10.1103/PhysRevResearch.2.023400}, author = {Ge, Wenchao and Jacobs, Kurt and Asiri, Saeed and Foss-Feig, Michael and Zubairy, M. Suhail} } @article { ISI:000530031700002, title = {Operator Levy Flight: Light Cones in Chaotic Long-Range Interacting Systems}, journal = {Phys. Rev. Lett.}, volume = {124}, number = {18}, year = {2020}, month = {MAY 4}, pages = {180601}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We argue that chaotic power-law interacting systems have emergent limits on information propagation, analogous to relativistic light cones, which depend on the spatial dimension d and the exponent a governing the decay of interactions. Using the dephasing nature of quantum chaos, we map the problem to a stochastic model with a known phase diagram. A linear light cone results for alpha >= d + 1/2. We also provide a Levy flight (long-range random walk) interpretation of the results and show consistent numerical data for 1D long-range spin models with 200 sites.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.124.180601}, author = {Zhou, Tianci and Xu, Shenglong and Chen, Xiao and Guo, Andrew and Swingle, Brian} } @article { ISI:000548284200010, title = {Optical clocks based on the Cf15+ and Cf17+ ions}, journal = {Phys. Rev. A}, volume = {102}, number = {1}, year = {2020}, month = {JUL 6}, pages = {012802}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Recent experimental progress in cooling, trapping, and quantum logic spectroscopy of highly charged ions (HCIs) made HCIs accessible for high-resolution spectroscopy and precision fundamental studies. Based on these achievements, we explore a possibility to develop optical clocks using transitions between the ground and a low-lying excited state in Cf15+ and Cf17+ ions. Using a high-accuracy relativistic method of calculation, we predicted the wavelengths of clock transitions, calculated relevant atomic properties, and analyzed a number of systematic effects (such as the electric quadrupole, micromotion, and quadratic Zeeman shifts of the clock transitions) that affect the accuracy and stability of the optical clocks. We also calculated magnetic dipole hyperfine-structure constants of the clock states and the blackbody radiation shifts of the clock transitions.}, issn = {1050-2947}, doi = {10.1103/PhysRevA.102.012802}, author = {Porsev, S. G. and Safronova, I, U. and Safronova, M. S. and Schmidt, P. O. and Bondarev, I, A. and Kozlov, M. G. and Tupitsyn, I. I. and Cheung, C.} } @article { ISI:000538714300009, title = {Optical enhancement of superconductivity via targeted destruction of charge density waves}, journal = {Phys. Rev. B}, volume = {101}, number = {22}, year = {2020}, month = {JUN 8}, pages = {224506}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {It has been experimentally established that the occurrence of charge density waves is a common feature of various underdoped cuprate superconducting compounds. The observed states, which are often found in the form of bond density waves (BDWs), usually occur in a temperature regime immediately above the superconducting transition temperature. Motivated by recent optical experiments on superconducting materials, where it has been shown that optical irradiation can transiently improve the superconducting features, here we propose an approach for the enhancement of superconductivity by the targeted destruction of the BDW order which we expect to be more efficient than the previous methods. Since BDW states are usually found in competition with superconductivity, suppression of the BDW order enhances the tendency of electrons to form Cooper pairs after reaching a steady state. By investigating the optical coupling of gapless, collective fluctuations of the BDW modes, we argue that the resonant excitation of these modes can melt the underlying BDW order parameter. We propose an experimental setup to implement such an optical coupling using two-dimensional plasmon-polariton hybrid systems.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.101.224506}, author = {Dehghani, Hossein and Raines, Zachary M. and Galitski, Victor M. and Hafezi, Mohammad} } @article { ISI:000527498000001, title = {Optical excitations in compressible and incompressible two-dimensional electron liquids}, journal = {Phys. Rev. B}, volume = {101}, number = {15}, year = {2020}, month = {APR 22}, pages = {155127}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Optically generated electron-hole pairs can probe strongly correlated electronic matter, or, by forming exciton-polaritons within an optical cavity, give rise to photonic nonlinearities. The present paper theoretically studies the properties of electron-hole pairs in a two-dimensional electron liquid in the fractional quantum Hall regime. In particular, we quantify the effective interactions between optical excitations by numerically evaluating the system{\textquoteright}s energy spectrum under the assumption of full spin and Landau level polarization. Optically most active are those pair excitations which do not modify the correlations of the electron liquid, also known as multiplicative states. In the case of spatial separation of electrons and holes, these excitations interact repulsively with each other. However, when the electron liquid is compressible, other nonmultiplicative configurations occur at lower energies. The interactions of such dark excitations strongly depend on the liquid, and can also become attractive. For the case of a single excitation, we also study the effect of Landau level mixing in the valence band which can dramatically change the effective mass of an exciton.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.101.155127}, author = {Grass, Tobias and Cotlet, Ovidiu and Imamoglu, Atac and Hafezi, Mohammad} } @article {kim_optical_2020, title = {Optical imprinting of superlattices in two-dimensional materials}, journal = {Phys. Rev. Res.}, volume = {2}, number = {4}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {oct}, abstract = {We propose an optical method of shining circularly polarized and spatially periodic laser fields to imprint superlattice structures in two-dimensional electronic systems. By changing the configuration of the optical field, we synthesize various lattice structures with different spatial symmetry, periodicity, and strength. We find that the wide optical tunability allows one to tune different properties of the effective band structure, including Chern number, energy bandwidths, and band gaps. The in situ tunability of the superlattice gives rise to unique physics ranging from the topological transitions to the creation of the flat bands through the kagome superlattice, which can allow a realization of strongly correlated phenomena in Floquet systems. We consider the high-frequency regime where the electronic system can remain in the quasiequilibrium phase for an extended amount of time. The spatiotemporal reconfigurability of the present scheme opens up possibilities to control light-matter interaction to generate novel electronic states and optoelectronic devices.}, doi = {10.1103/PhysRevResearch.2.043004}, author = {Kim, Hwanmun and Dehghani, Hossein and Aoki, Hideo and Martin, Ivar and Hafezi, Mohammad} } @article { ISI:000542514200007, title = {Phonon scattering induced carrier resistivity in twisted double-bilayer graphene}, journal = {Phys. Rev. B}, volume = {101}, number = {24}, year = {2020}, month = {JUN 24}, pages = {245436}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {In this work we carry out a theoretical study of the phonon-induced resistivity in twisted double bilayer graphene (TDBG), in which two Bernal-stacked bilayer graphene devices are rotated relative to each other by a small angle theta. We show that at small twist angles (theta similar to 1 degrees) the effective mass of the TDBG system is greatly enhanced, leading to a drastically increased phonon-induced resistivity in the high-temperature limit where phonon scattering leads to a linearly increasing resistivity with increasing temperature. We also discuss possible implications of our theory on superconductivity in such a system and provide an order of magnitude estimation of the superconducting transition temperature.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.101.245436}, author = {Li, Xiao and Wu, Fengcheng and Das Sarma, S.} } @article {rylands_photon-mediated_2020, title = {Photon-{Mediated} {Peierls} {Transition} of a {1D} {Gas} in a {Multimode} {Optical} {Cavity}}, journal = {Phys. Rev. Lett.}, volume = {125}, number = {1}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {jul}, abstract = {The Peierls instability toward a charge density wave is a canonical example of phonon-driven strongly correlated physics and is intimately related to topological quantum matter and exotic superconductivity. We propose a method for realizing an analogous photon-mediated Peierls transition, using a system of one-dimensional tubes of interacting Bose or Fermi atoms trapped inside a multimode confocal cavity. Pumping the cavity transversely engineers a cavity-mediated metal-to-insulator transition in the atomic system. For strongly interacting bosons in the Tonks-Girardeau limit, this transition can be understood (through fermionization) as being the Peierls instability. We extend the calculation to finite values of the interaction strength and derive analytic expressions for both the cavity field and mass gap. They display nontrivial power law dependence on the dimensionless matter-light coupling.

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.125.010404}, author = {Rylands, Colin and Guo, Yudan and Lev, Benjamin L. and Keeling, Jonathan and Galitski, Victor} } @article {16931, title = {Photon propagation through dissipative Rydberg media at large input rates}, journal = {Phys. Rev. Research}, volume = {2}, year = {2020}, month = {Jul}, pages = {033049}, abstract = {We study the dissipative propagation of quantized light in interacting Rydberg media under the conditions of electromagnetically induced transparency. Rydberg blockade physics in optically dense atomic media leads to strong dissipative interactions between single photons. The regime of high incoming photon flux constitutes a challenging many-body dissipative problem. We experimentally study in detail the pulse shapes and the second-order correlation function of the outgoing field and compare our data with simulations based on two novel theoretical approaches well-suited to treat this many-photon limit. At low incoming flux, we report good agreement between both theories and the experiment. For higher input flux, the intensity of the outgoing light is lower than that obtained from theoretical predictions. We explain this discrepancy using a simple phenomenological model taking into account pollutants, which are nearly stationary Rydberg excitations coming from the reabsorption of scattered probe photons. At high incoming photon rates, the blockade physics results in unconventional shapes of measured correlation functions.

}, keywords = {Models, Photonics}, doi = {10.1103/PhysRevResearch.2.033049}, url = {https://link.aps.org/doi/10.1103/PhysRevResearch.2.033049}, author = {Bienias, Przemyslaw and Douglas, James and Paris-Mandoki, Asaf and Titum, Paraj and Mirgorodskiy, Ivan and Tresp, Christoph and Zeuthen, Emil and Gullans, Michael J. and Manzoni, Marco and Hofferberth, Sebastian and Chang, Darrick and Gorshkov, Alexey V.} } @article { ISI:000517742600004, title = {Photonic materials in circuit quantum electrodynamics}, journal = {Nat. Phys.}, volume = {16}, number = {3}, year = {2020}, month = {MAR}, pages = {268-279}, publisher = {NATURE PUBLISHING GROUP}, type = {Review}, abstract = {Photonic synthetic materials provide an opportunity to explore the role of microscopic quantum phenomena in determining macroscopic material properties. There are, however, fundamental obstacles to overcome - in vacuum, photons not only lack mass, but also do not naturally interact with one another. Here, we review how the superconducting quantum circuit platform has been harnessed in the last decade to make some of the first materials from light. We describe the structures that are used to imbue individual microwave photons with matter-like properties such as mass, the nonlinear elements that mediate interactions between these photons, and quantum dynamic/thermodynamic approaches that can be used to assemble and stabilize strongly correlated states of many photons. We then describe state-of-the-art techniques to generate synthetic magnetic fields, engineer topological and non-topological flat bands and explore the physics of quantum materials in non-Euclidean geometries - directions that we view as some of the most exciting for this burgeoning field. Finally, we discuss upcoming prospects, and in particular opportunities to probe novel aspects of quantum thermalization and detect quasi-particles with exotic anyonic statistics, as well as potential applications in quantum information science. This Review Article surveys the physics of many-body quantum states formed by microwave photons in circuit quantum electrodynamics environments.}, issn = {1745-2473}, doi = {10.1038/s41567-020-0815-y}, author = {Carusotto, Iacopo and Houck, Andrew A. and Kollar, Alicia J. and Roushan, Pedram and Schuster, David I. and Simon, Jonathan} } @article {16911, title = {Photon-Mediated Peierls Transition of a 1D Gas in a Multimode Optical Cavity}, journal = {Phys. Rev. Lett.}, volume = {125}, year = {2020}, month = {Jul}, pages = {010404}, abstract = {The Peierls instability toward a charge density wave is a canonical example of phonon-driven strongly correlated physics and is intimately related to topological quantum matter and exotic superconductivity. We propose a method for realizing an analogous photon-mediated Peierls transition, using a system of one-dimensional tubes of interacting Bose or Fermi atoms trapped inside a multimode confocal cavity. Pumping the cavity transversely engineers a cavity-mediated metal-to-insulator transition in the atomic system. For strongly interacting bosons in the Tonks-Girardeau limit, this transition can be understood (through fermionization) as being the Peierls instability. We extend the calculation to finite values of the interaction strength and derive analytic expressions for both the cavity field and mass gap. They display nontrivial power law dependence on the dimensionless matter-light coupling.

}, doi = {10.1103/PhysRevLett.125.010404}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.125.010404}, author = {Rylands, Colin and Guo, Yudan and Lev, Benjamin L. and Keeling, Jonathan and Galitski, Victor} } @article {pan_physical_2020, title = {Physical mechanisms for zero-bias conductance peaks in {Majorana} nanowires}, journal = {Phys. Rev. Res.}, volume = {2}, number = {1}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {mar}, abstract = {Motivated by the need to understand and simulate the ubiquitous experimentally observed zero-bias conductance peaks in superconductor-semiconductor hybrid structures, we theoretically investigate the tunneling conductance spectra in one-dimensional nanowires in proximity to superconductors in a systematic manner taking into account several different physical mechanisms producing zero-bias conductance peaks. The mechanisms we consider are the presence of quantum dots, inhomogeneous potential, random disorder in the chemical potential, random fluctuations in the superconducting gap, and in the effective g factor with the self-energy renormalization induced by the parent superconductor in both short (L similar to 1 mu m) and long nanowires (L similar to 3 mu m). We classify all foregoing theoretical results for zero-bias conductance peaks into three types: the good, the bad, and the ugly, according to the physical mechanisms producing the zero-bias peaks and their topological properties. We find that, although the topological Majorana zero modes are immune to weak disorder, strong disorder ({\textquotedblright}ugly{\textquotedblright}) completely suppresses topological superconductivity and generically leads to trivial zero-bias peaks. Compared qualitatively with the extensive existing experimental results in the superconductor-semiconductor nanowire structures, we conclude that most current experiments are likely exploring trivial zero-bias peaks in the {\textquotedblleft}ugly{\textquotedblright} situation dominated by strong disorder. We also study the nonlocal end-to-end correlation measurement in both the short and long wires, and point out the limitation of the nonlocal correlation in ascertaining topological properties particularly when applied to short wires. Although we present results for {\textquotedblleft}good{\textquotedblright} and {\textquotedblleft}bad{\textquotedblright} zero-bias peaks, arising respectively from topological Majorana bound states and trivial Andreev bound states, strictly for the sake of direct comparison with the {\textquotedblleft}ugly{\textquotedblright} zero-bias conductance peaks arising from strong disorder, the main goal of the current work is to establish with a very high confidence level the real physical possibility that essentially all experimentally observed zero-bias peaks in Majorana nanowires are most likely ugly, i.e., purely induced by strong disorder, and are as such utterly nontopological. Our work clearly suggests that an essential prerequisite for any future observation of topological Majorana zero modes in nanowires is a substantialmaterials improvement of the semiconductor-superconductor hybrid systems leading to much cleaner wires.}, doi = {10.1103/PhysRevResearch.2.013377}, author = {Pan, Haining and Das Sarma, S.} } @conference {moille_post-processing_2020, title = {Post-{Processing} {Dispersion} {Engineering} of {Frequency} {Combs} {In} {Microresonator} {Addressing} {Atomic} {Clock}}, booktitle = {Conference on Lasers and Electro-Optics (CLEO)}, series = {Conference on {Lasers} and {Electro}-{Optics}}, year = {2020}, note = {Backup Publisher: IEEE ISSN: 2160-9020 Type: Proceedings Paper}, publisher = {IEEE}, organization = {IEEE}, abstract = {We study Si3N4 microresonator frequency comb to address atomic transition in the visible. We show that thanks to our air-clad system, post-process dispersion engineering through trimming allows precise control of the dispersive wave position. (C) 2020 The Author(s)

}, isbn = {978-1-943580-76-7}, author = {Moille, Gregory and Lu, Xiyuan and Rao, Ashutosh and Weedy, Daron and Srinivasan, Kartik} } @article { ISI:000555932400003, title = {Probing the relaxed relaxion at the luminosity and precision frontiers}, journal = {J. High Energy Phys.}, number = {7}, year = {2020}, month = {JUL 22}, pages = {153}, publisher = {SPRINGER}, type = {Article}, abstract = {Cosmological relaxation of the electroweak scale is an attractive scenario relaxion, is a light spin-zero field which dynamically relaxes the Higgs mass with respect to its natural large value. We show that the relaxion is generically stabilized at a special position in the field space, which leads to suppression of its mass and potentially unnatural values for the model{\textquoteright}s effective low-energy couplings. In particular, we find that the relaxion mixing with the Higgs can be several orders of magnitude above its naive naturalness bound. Low energy observers may thus find the relaxion theory being fine-tuned although the relaxion scenario itself is constructed in a technically natural way. More generally, we identify the lower and upper bounds on the mixing angle. We examine the experimental implications of the above observations at the luminosity and precision frontiers. A particular attention is given to the impressive ability of future nuclear clocks to search for rapidly oscillating scalar ultra-light dark matter, where the future projected sensitivity is presented.}, keywords = {Beyond Standard Model, Cosmology of Theories beyond the SM}, issn = {1029-8479}, doi = {10.1007/JHEP07(2020)153}, author = {Banerjee, Abhishek and Kim, Hyungjin and Matsedonskyi, Oleksii and Perez, Gilad and Safronova, Marianna S.} } @article { ISI:000567752300004, title = {Probing XY phase transitions in a Josephson junction array with tunable frustration}, journal = {Phys. Rev. B}, volume = {102}, number = {9}, year = {2020}, month = {SEP 10}, pages = {094509}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The seminal theoretical works of Berezinskii, Kosterlitz, and Thouless presented a paradigm for phase transitions in condensed matter that are driven by topological excitations. These transitions have been extensively studied in the context of two-dimensional XY models-coupled compasses-and have generated interest in the context of quantum simulation. Here, we use a circuit quantum-electrodynamics architecture to study the critical behavior of engineered XY models through their dynamical response. In particular, we examine not only the unfrustrated case but also the fully frustrated case which leads to enhanced degeneracy associated with the spin rotational {[}U(1)] and discrete chiral (Z(2)) symmetries. The nature of the transition in the frustrated case has posed a challenge for theoretical studies while direct experimental probes remain elusive. Here we identify the transition temperatures for both the unfrustrated and fully frustrated XY models by probing a Josephson junction array close to equilibrium using weak microwave excitations and measuring the temperature dependence of the effective damping obtained from the complex reflection coefficient. We argue that our probing technique is primarily sensitive to the dynamics of the U(1) part.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.094509}, author = {Cosmic, R. and Kawabata, K. and Ashida, Y. and Ikegami, H. and Furukawa, S. and Patil, P. and Taylor, J. M. and Nakamura, Y.} } @article {eller_producing_2020, title = {Producing flow in racetrack atom circuits by stirring}, journal = {Phys. Rev. A}, volume = {102}, number = {6}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {dec}, abstract = {We present a study of how macroscopic flow can be produced in Bose-Einstein condensates confined in a {\textquotedblleft}racetrack{\textquotedblright} potential by stirring with a wide rectangular barrier. This potential consists of two half-circle channels separated by straight channels of length L and reduces to a ring potential if L = 0. We present the results of a flow-production study where racetrack condensates were stirred with a barrier under varying conditions of barrier height, stir speed, racetrack geometry, and temperature. The result was that stirring was readily able to produce flow in ring and nonring geometries but that the exact amount of flow produced depended on all of the study parameters. We therefore investigated the mechanism by which flow was produced in the stirring process. The basic mechanism that we discovered was that when the sweeping barrier potential height reached a critical value a series of phase slip (i.e., a sudden change in the phase winding around the condensate midtrack) events occurred. Phase slipping stopped when the flow produced overtook the speed of the stirring barrier. Disturbances generated at each phase slip circulated around the channel and served to convert the initially localized velocity distribution into smooth macroscopic flow. This picture of the mechanism for making flow should facilitate the design of closed-channel atom circuits for creating a desired amount of quantized smooth flow on demand.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.102.063324}, author = {Eller, Benjamin and Oladehin, Olatunde and Fogarty, Daniel and Heller, Clayton and Clark, Charles W. and Edwards, Mark} } @article {17151, title = {Proposal for gravitational direct detection of dark matter}, journal = {Phys. Rev. D}, volume = {102}, year = {2020}, month = {Oct}, pages = {072003}, doi = {10.1103/PhysRevD.102.072003}, url = {https://link.aps.org/doi/10.1103/PhysRevD.102.072003}, author = {Carney, Daniel and Ghosh, Sohitri and Krnjaic, Gordan and Taylor, Jacob M.} } @article {pagano_quantum_2020, title = {Quantum approximate optimization of the long-range {Ising} model with a trapped-ion quantum simulator}, journal = {Proc. Natl. Acad. Sci. U. S. A.}, volume = {117}, number = {41}, year = {2020}, note = {Place: 2101 CONSTITUTION AVE NW, WASHINGTON, DC 20418 USA Publisher: NATL ACAD SCIENCES Type: Article}, month = {oct}, pages = {25396{\textendash}25401}, abstract = {Quantum computers and simulators may offer significant advantages over their classical counterparts, providing insights into quantum many-body systems and possibly improving performance for solving exponentially hard problems, such as optimization and satisfiability. Here, we report the implementation of a low-depth Quantum Approximate Optimization Algorithm (QAOA) using an analog quantum simulator. We estimate the ground-state energy of the Transverse Field Ising Model with long-range interactions with tunable range, and we optimize the corresponding combinatorial classical problem by sampling the QAOA output with high-fidelity, single-shot, individual qubit measurements. We execute the algorithm with both an exhaustive search and closed-loop optimization of the variational parameters, approximating the ground-state energy with up to 40 trapped-ion qubits. We benchmark the experiment with bootstrapping heuristic methods scaling polynomially with the system size. We observe, in agreement with numerics, that the QAOA performance does not degrade significantly as we scale up the system size and that the runtime is approximately independent from the number of qubits. We finally give a comprehensive analysis of the errors occurring in our system, a crucial step in the path forward toward the application of the QAOA to more general problem instances.}, keywords = {computing, quantum, quantum algorithms, quantum information science, quantum simulation, trapped ions}, issn = {0027-8424}, doi = {10.1073/pnas.2006373117}, author = {Pagano, Guido and Bapat, Aniruddha and Becker, Patrick and Collins, Katherine S. and De, Arinjoy and Hess, Paul W. and Kaplan, Harvey B. and Kyprianidis, Antonis and Tan, Wen Lin and Baldwin, Christopher and Brady, Lucas T. and Deshpande, Abhinav and Liu, Fangli and Jordan, Stephen and Gorshkov, V, Alexey and Monroe, Christopher} } @article { ISI:000519631000004, title = {Quantum Brownian motion of a particle from Casimir-Polder interactions}, journal = {Phys. Rev. A}, volume = {101}, number = {3}, year = {2020}, month = {MAR 13}, pages = {032507}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study the fluctuation-induced dissipative dynamics of the quantized center-of-mass motion of a polarizable dielectric particle trapped near a surface. The particle{\textquoteright}s center of mass is treated as an open quantum system coupled to the electromagnetic field acting as its environment, with the resulting system dynamics described by a quantum Brownian motion master equation. The dissipation and decoherence of the particle{\textquoteright}s center of mass are characterized by the modified spectral density of the electromagnetic field that depends on surface losses and the strength of the classical trap field. Our results are relevant to experiments with levitated dielectric particles near surfaces, illustrating potential ways of mitigating fluctuation-induced decoherence while preparing such systems in macroscopic quantum states.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.101.032507}, author = {Sinha, Kanupriya and Subasi, Yigit} } @article { ISI:000513110500015, title = {Quantum cascade laser lives on the edge}, journal = {Nature}, volume = {578}, number = {7794}, year = {2020}, month = {FEB}, pages = {219-220}, publisher = {NATURE PUBLISHING GROUP}, type = {Editorial Material}, abstract = {Devices known as quantum cascade lasers produce useful terahertz radiation, but are typically highly sensitive to fabrication defects. This limitation has now been overcome using a property called topological robustness. Terahertz radiation from a topological laser.}, issn = {0028-0836}, author = {Mittal, Sunil and Waks, Edo} } @article { ISI:000576889300001, title = {Quantum geometry and stability of moire flatband ferromagnetism}, journal = {Phys. Rev. B}, volume = {102}, number = {16}, year = {2020}, month = {OCT 12}, pages = {165118}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Several moire systems created by various twisted bilayers have manifested magnetism under flatband conditions leading to enhanced interaction effects. We theoretically study stability of moire flatband ferromagnetism against collective excitations, with a focus on the effects of Bloch band quantum geometry. The spin magnon spectrum is calculated using different approaches, including Bethe-Salpeter equation, single mode approximation, and an analytical theory. One of our main results is an analytical expression for the spin stiffness in terms of the Coulomb interaction potential, the Berry curvatures, and the quantum metric tensor, where the last two quantities characterize the quantum geometry of moire bands. This analytical theory shows that Berry curvatures play an important role in stiffening the spin magnons. Furthermore, we construct an effective field theory for the magnetization fluctuations and show explicitly that skyrmion excitations bind an integer number of electrons that is proportional to the Bloch band Chern number and the skyrmion winding number.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.165118}, author = {Wu, Fengcheng and Das Sarma, S.} } @article { ISI:000519638100001, title = {Quantum Hall resistance dartboards using graphene p-n junction devices with Corbino geometries}, journal = {AIP Adv.}, volume = {10}, number = {3}, year = {2020}, month = {MAR 1}, pages = {035205}, publisher = {AMER INST PHYSICS}, type = {Article}, abstract = {The use of multiple current terminals on millimeter-scale graphene p-n junction devices fabricated with Corbino geometries, or quantum Hall resistance dartboards, has enabled the measurement of several fractional multiples of the quantized Hall resistance at the nu = 2 plateau (R-H approximate to 12 906 Omega). Experimentally obtained values agreed with the corresponding numerical simulations performed with the LTspice circuit simulator. More complicated designs of the quantum Hall resistance dartboard were simulated to establish the potential parameter space within which these Corbino-type devices could output resistance. Most importantly, these measurements support simpler processes of ultraviolet lithography as a more efficient means of scaling up graphene-based device sizes while maintaining sufficiently narrow junctions. (c) 2020 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).}, doi = {10.1063/1.5136315}, author = {Liu, I, C- and Patel, D. K. and Marzano, M. and Kruskopf, M. and Hill, H. M. and Rigosi, A. F.} } @article { ISI:000506585800002, title = {Quantum Lifshitz criticality in a frustrated two-dimensional XY model}, journal = {Phys. Rev. B}, volume = {101}, number = {3}, year = {2020}, month = {JAN 9}, pages = {035114}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Antiferromagnetic quantum spin systems can exhibit a transition between collinear and spiral ground states, driven by frustration. Classically this is a smooth crossover and the crossover point is termed a Lifshitz point. Quantum fluctuations change the nature of the transition. In particular, it has been argued previously that in the two-dimensional (2D) case a spin liquid (SL) state is developed in the vicinity of the Lifshitz point, termed a Lifshitz SL. In the present work, using a field theory approach, we solve the Lifshitz quantum phase transition problem for the 2D frustrated XY model. Specifically, we show that, unlike the SU(2) symmetric Lifshitz case, in the XY model, the SL exists only at the critical point. At zero temperature we calculate nonuniversal critical exponents in the Neel and in the spin spiral state and relate these to properties of the SL. We also solve the transition problem at a finite temperature and discuss the role of topological excitations.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.101.035114}, author = {Kharkov, Yaroslav A. and Oitmaa, Jaan and Sushkov, Oleg P.} } @inbook {solomon_quantum_2020, title = {Quantum light from optically dressed quantum dot states in microcavities}, booktitle = {Semiconductor Quantum Science and Technology}, series = {Semiconductors and {Semimetals}}, volume = {105}, year = {2020}, note = {ISSN: 0080-8784 Journal Abbreviation: Semicond. Semimet. Type: Article; Book Chapter}, pages = {305{\textendash}346}, publisher = {ELSEVIER ACADEMIC PRESS INC}, organization = {ELSEVIER ACADEMIC PRESS INC}, isbn = {978-0-12-823773-1}, doi = {10.1016/bs.semsem.2020.10.004}, author = {Solomon, Glenn S. and Muller, Andreas and Flagg, Edward}, editor = {Cundiff, ST and Kira, M} } @conference {hao_quantum_2020, title = {Quantum {Limits} of {Optical} {Beam} {Deflection} {Measurements} of a {Nanomechanical} {Resonator}}, booktitle = {Conference on Lasers and Electro-Optics (CLEO)}, series = {Conference on {Lasers} and {Electro}-{Optics}}, year = {2020}, note = {Backup Publisher: IEEE ISSN: 2160-9020 Type: Proceedings Paper}, publisher = {IEEE}, organization = {IEEE}, abstract = {Optical lever detection is a simple and robust method to measure small displacements. We report on our experimental efforts toward reaching and surpassing the quantum backaction limits of this method when probing a high Q nanomechanical resonator. (C) 2020 The Author(s)

}, isbn = {978-1-943580-76-7}, author = {Hao, Shan and Singh, Robinjeet and Purdy, Thomas P.} } @article { ISI:000510146100001, title = {Quantum many-body scar states with emergent kinetic constraints and finite-entanglement revivals}, journal = {Phys. Rev. B}, volume = {101}, number = {2}, year = {2020}, month = {JAN 29}, pages = {024306}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We construct a set of exact, highly excited eigenstates for a nonintegrable spin-1/2 model in one dimension that is relevant to experiments on Rydberg atoms in the antiblockade regime. These states provide a new solvable example of quantum many-body scars: their sub-volume-law entanglement and equal energy spacing allow for infinitely long-lived coherent oscillations of local observables following a suitable quantum quench. While previous works on scars have interpreted such oscillations in terms of the precession of an emergent macroscopic SU(2) spin, the present model evades this description due to a set of emergent kinetic constraints in the scarred eigenstates that are absent in the underlying Hamiltonian. We also analyze the set of initial states that give rise to periodic revivals, which persist as approximate revivals on a finite timescale when the underlying model is perturbed. Remarkably, a subset of these initial states coincides with the family of area-law entangled Rokhsar-Kivelson states shown by Lesanovsky to be exact ground states for a class of models relevant to experiments on Rydberg-blockaded atomic lattices.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.101.024306}, author = {Iadecola, Thomas and Schecter, Michael} } @article {zhu_quantum_2020, title = {Quantum origami: {Transversal} gates for quantum computation and measurement of topological order}, journal = {Phys. Rev. Res.}, volume = {2}, number = {1}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {mar}, abstract = {In topology, a torus remains invariant under certain nontrivial transformations known as modular transformations. In the context of topologically ordered quantum states of matter supported on a torus geometry in real space, these transformations encode the braiding statistics and fusion rules of emergent anyonic excitations and thus serve as a diagnostic of topological order. Moreover, modular transformations of higher genus surfaces, e.g., a torus with multiple handles, can enhance the computational power of a topological state, in many cases providing a universal fault-tolerant set of gates for quantum computation. However, due to the intrusive nature of modular transformations, which abstractly involve global operations, physical implementations of them in local systems have remained elusive. Here, we show that by engineering an effectively folded manifold corresponding to a multilayer topological system, modular transformations can be applied in a single shot by independent local unitaries, providing a novel class of transversal logical gates for fault-tolerant quantum computation. Specifically, we demonstrate that multilayer topological states with appropriate boundary conditions and twist defects allow modular transformations to be effectively implemented by a finite sequence of local SWAP gates between the layers. We further provide methods to directly measure the modular matrices, and thus the fractional statistics of anyonic excitations, providing a novel way to directly measure topological order. A more general theory of transversal gates and the deep connection to anyon symmetry transformation and symmetry-enriched topological orders are also discussed.}, doi = {10.1103/PhysRevResearch.2.013285}, author = {Zhu, Guanyu and Hafezi, Mohammad and Barkeshli, Maissam} } @article { ISI:000570957900002, title = {Quantum oscillations from networked topological interfaces in a Weyl semimetal}, journal = {npj Quantum Mater.}, volume = {5}, number = {1}, year = {2020}, month = {SEP 7}, pages = {62}, publisher = {NATURE PUBLISHING GROUP}, type = {Article}, abstract = {Layered transition metal chalcogenides are promising hosts of electronic Weyl nodes and topological superconductivity. MoTe(2)is a striking example that harbors both noncentrosymmetric T(d)and centrosymmetric T{\textquoteright} phases, both of which have been identified as topologically nontrivial. Applied pressure tunes the structural transition separating these phases to zero temperature, stabilizing a mixed T-d-T{\textquoteright} matrix that entails a network of interfaces between the two nontrivial topological phases. Here, we show that this critical pressure range is characterized by distinct coherent quantum oscillations, indicating that the difference in topology between topologically nonvtrivial T(d)and T{\textquoteright} phases gives rise to an emergent electronic structure: a network of topological interfaces. A rare combination of topologically nontrivial electronic structures and locked-in transformation barriers leads to this counterintuitive situation, wherein quantum oscillations can be observed in a structurally inhomogeneous material. These results further open the possibility of stabilizing multiple topological phases coexisting with superconductivity.}, doi = {10.1038/s41535-020-00264-8}, author = {Liu, I-Lin and Heikes, Colin and Yildirim, Taner and Eckberg, Chris and Metz, Tristin and Kim, Hyunsoo and Ran, Sheng and Ratcliff, William D. and Paglione, Johnpierre and Butch, Nicholas P.} } @article {17096, title = {Quantum simulation of hyperbolic space with circuit quantum electrodynamics: From graphs to geometry}, journal = {Phys. Rev. A}, volume = {102}, year = {2020}, month = {Sep}, pages = {032208}, abstract = {We show how quantum many-body systems on hyperbolic lattices with nearest-neighbor hopping and local interactions can be mapped onto quantum field theories in continuous negatively curved space. The underlying lattices have recently been realized experimentally with superconducting resonators and therefore allow for a table-top quantum simulation of quantum physics in curved background. Our mapping provides a computational tool to determine observables of the discrete system even for large lattices, where exact diagonalization fails. As an application and proof of principle we quantitatively reproduce the ground state energy, spectral gap, and correlation functions of the noninteracting lattice system by means of analytic formulas on the Poincar{\'e} disk, and show how conformal symmetry emerges for large lattices. This sets the stage for studying interactions and disorder on hyperbolic graphs in the future. Importantly, our analysis reveals that even relatively small discrete hyperbolic lattices emulate the continuous geometry of negatively curved space, and thus can be used to experimentally resolve fundamental open problems at the interface of interacting many-body systems, quantum field theory in curved space, and quantum gravity.

}, keywords = {hyperbolic geometry, quantum simulation}, doi = {10.1103/PhysRevA.102.032208}, url = {https://link.aps.org/doi/10.1103/PhysRevA.102.032208}, author = {Boettcher, Igor and Bienias, Przemyslaw and Belyansky, Ron and Kollar, Alicia J. and Gorshkov, Alexey V.} } @article {anastopoulos_quantum_2020, title = {Quantum superposition of two gravitational cat states}, journal = {Class. Quantum Gravity}, volume = {37}, number = {23}, year = {2020}, note = {Place: TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND Publisher: IOP PUBLISHING LTD Type: Article}, month = {dec}, abstract = {We extend our earlier work [1] on probing a gravitational cat state (gravcat) to the quantum superposition of two gravcats in an exemplary model and in Bose-Einstein condensates (BEC). In addition to its basic theoretical values in gravitational quantum physics and macroscopic quantum phenomena, this investigation can provide some theoretical support to experimental proposals for measuring gravity-induced entanglement and the quantum nature of perturbative gravity. In the first part we consider cat states generated by double-well potentials. A pair of gravcats, each approximated as a two-level system, is characterized by gravity-induced Rabi oscillations, and by gravity-induced entanglement of its energy eigenstates. In the second part we turn to a (non-relativistic) quantum field theory description and derive a gravitational Gross-Pitaevsky equation for gravcats formed in BEC. Using a mathematical analogy to quantum rotors, we explore the properties of the two-gravcat system for BECs, its physical consequences and observational possibilities. Finally we discuss our results in comparison to predictions of alternative quantum theories, and we explain their implications.}, keywords = {Bose Einstein condensates, entanglement, gravitational decoherence, gravitational quantum physics, quantum superpositions}, issn = {0264-9381}, doi = {10.1088/1361-6382/abbe6f}, author = {Anastopoulos, C. and Hu, B. L.} } @article { ISI:000556360300013, title = {Quantum walks and Dirac cellular automata on a programmable trapped-ion quantum computer}, journal = {Nat. Commun.}, volume = {11}, number = {1}, year = {2020}, month = {JUL 24}, pages = {3720}, publisher = {NATURE PUBLISHING GROUP}, type = {Article}, abstract = {The quantum walk formalism is a widely used and highly successful framework for modeling quantum systems, such as simulations of the Dirac equation, different dynamics in both the low and high energy regime, and for developing a wide range of quantum algorithms. Here we present the circuit-based implementation of a discrete-time quantum walk in position space on a five-qubit trapped-ion quantum processor. We encode the space of walker positions in particular multi-qubit states and program the system to operate with different quantum walk parameters, experimentally realizing a Dirac cellular automaton with tunable mass parameter. The quantum walk circuits and position state mapping scale favorably to a larger model and physical systems, allowing the implementation of any algorithm based on discrete-time quantum walks algorithm and the dynamics associated with the discretized version of the Dirac equation.}, issn = {2041-1723}, doi = {10.1038/s41467-020-17519-4}, author = {Alderete, C. Huerta and Singh, Shivani and Nhung H Nguyen and Zhu, Daiwei and Balu, Radhakrishnan and Monroe, Christopher and Chandrashekar, C. M. and Linke, Norbert M.} } @article { ISI:000555323500001, title = {Quenched vs Annealed: Glassiness from SK to SYK}, journal = {Phys. Rev. X}, volume = {10}, number = {3}, year = {2020}, month = {AUG 4}, pages = {031026}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We show that any Sachdev-Ye-Kitaev- (SYK) like model with finite-body interactions among local degrees of freedom, e.g., bosons or spins, has a fundamental difference from the standard fermionic model: The former model fails to be described by an annealed free energy at low temperature. In this respect, such models more closely resemble spin glasses. We demonstrate this by two means: first, a general theorem proving that the annealed free energy is divergent at low temperature in any model with a tensor product Hilbert space, and second, a replica treatment of two prominent examples which exhibit phase transitions from an {\textquoteleft}{\textquoteleft}annealed{{\textquoteright}{\textquoteright}} phase to a {\textquoteleft}{\textquoteleft}nonannealed{{\textquoteright}{\textquoteright}} phase as a function of the temperature. We further show that this effect appears only at O(N)th order in a 1/N expansion, even though lower-order terms misleadingly seem to converge. Our results prove that the nonbosonic nature of the particles in the SYK model is an essential ingredient for its physics, highlight connections between local models and spin glasses, and raise important questions as to the role of fermions and/or glassiness in holography.}, issn = {2160-3308}, doi = {10.1103/PhysRevX.10.031026}, author = {Baldwin, C. L. and Swingle, B.} } @article {barker_radiofrequency_2020, title = {A radiofrequency voltage-controlled current source for quantum spin manipulation}, journal = {Rev. Sci. Instrum.}, volume = {91}, number = {10}, year = {2020}, note = {Place: 1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA Publisher: AMER INST PHYSICS Type: Article}, month = {oct}, abstract = {We present a wide-bandwidth, voltage-controlled current source that is easily integrated with radiofrequency magnetic field coils. Our design uses current feedback to compensate for the frequency-dependent impedance of a radiofrequency antenna. We are able to deliver peak currents greater than 100 mA over a 300 kHz to 54 MHz frequency span. The radiofrequency current source fits onto a printed circuit board smaller than 4 cm(2) and consumes less than 1.3 W of power. It is suitable for use in deployable quantum sensors and nuclear magnetic resonance systems.}, issn = {0034-6748}, doi = {10.1063/5.0011813}, author = {Barker, D. S. and Restelli, A. and Fedchak, J. A. and Scherschligt, J. and Eckel, S.} } @article {caravelli_random_2020, title = {Random quantum batteries}, journal = {Phys. Rev. Res.}, volume = {2}, number = {2}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {apr}, abstract = {Quantum nanodevices are fundamental systems in quantum thermodynamics that have been the subject of profound interest in recent years. Among these, quantum batteries play a very important role. In this paper we lay down a theory of random quantum batteries and provide a systematic way of computing the average work and work fluctuations in such devices by investigating their typical behavior. We show that the performance of random quantum batteries exhibits typicality and depends only on the spectral properties of the time evolving operator, the initial state, and the measuring Hamiltonian. At given revival times a random quantum battery features a quantum advantage over classical random batteries. Our method is particularly apt to be used both for exactly solvable models like the Jaynes-Cummings model or in perturbation theory, e.g., systems subject to harmonic perturbations. We also study the setting of quantum adiabatic random batteries.}, doi = {10.1103/PhysRevResearch.2.023095}, author = {Caravelli, Francesco and Coulter-De Wit, Ghislaine and Pedro Garcia-Pintos, Luis and Hamma, Alioscia} } @article {anderson_realization_2020, title = {Realization of a deeply subwavelength adiabatic optical lattice}, journal = {Phys. Rev. Res.}, volume = {2}, number = {1}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {feb}, abstract = {We propose and describe our realization of a deeply subwavelength optical lattice for ultracold neutral atoms using N resonantly Raman-coupled internal degrees of freedom. Although counterpropagating lasers with wavelength. provided two-photon Raman coupling, the resultant lattice period was lambda/2N, an N-fold reduction as compared to the conventional lambda/2 lattice period. We experimentally demonstrated this lattice built from the three F = 1 Zeeman states of a Rb-87 Bose-Einstein condensate, and generated a lattice with a lambda/6 = 132 nm period from lambda = 790 nm lasers. Lastly, we show that adding an additional rf-coupling field converts this lattice into a superlattice with N wells uniformly spaced within the original lambda/2 unit cell.}, doi = {10.1103/PhysRevResearch.2.013149}, author = {Anderson, R. P. and Trypogeorgos, D. and Valdes-Curiel, A. and Liang, Q-Y and Tao, J. and Zhao, M. and Andrijauskas, T. and Juzeliunas, G. and Spielman, I. B.} } @article { ISI:000526522500002, title = {Realization of a stroboscopic optical lattice for cold atoms with subwavelength spacing}, journal = {Phys. Rev. A}, volume = {101}, number = {4}, year = {2020}, month = {APR 17}, pages = {041603}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Optical lattices are typically created via the ac Stark shift and are limited by diffraction to periodicities >= lambda/2, where. is the wavelength of light used to create them. Lattices with smaller periodicities may be useful for many-body physics with cold atoms and can be generated by stroboscopic application of a phase-shifted lattice with subwavelength features. Here we demonstrate a lambda/4-spaced lattice by stroboscopically applying optical Kronig-Penney-like potentials which are generated using spatially dependent dark states. We directly probe the periodicity of the lambda/4-spaced lattice by measuring the average probability density of the atoms loaded into the ground band of the lattice. We measure lifetimes of atoms in this lattice and discuss the mechanisms that limit the applicability of this stroboscopic approach.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.101.041603}, author = {Tsui, T-C and Wang, Y. and Subhankar, S. and Porto, V, J. and Rolston, S. L.} } @article { ISI:000550577700002, title = {Real-time dynamics of string breaking in quantum spin chains}, journal = {Phys. Rev. B}, volume = {102}, number = {1}, year = {2020}, month = {JUL 21}, pages = {014308}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {String breaking is a central dynamical process in theories featuring confinement, where a string connecting two charges decays at the expense of the creation of new particle-antiparticle pairs. Here, we show that this process can also be observed in quantum Ising chains where domain walls get confined either by a symmetry-breaking field or by long-range interactions. We find that string breaking occurs, in general, as a two-stage process. First, the initial charges remain essentially static and stable. The connecting string, however, can become a dynamical object. We develop an effective description of this motion, which we find is strongly constrained. In the second stage, which can be severely delayed due to these dynamical constraints, the string finally breaks. We observe that the associated timescale can depend crucially on the initial separation between domain walls and can grow by orders of magnitude by changing the distance by just a few lattice sites. We discuss how our results generalize to one-dimensional confining gauge theories and how they can be made accessible in quantum simulator experiments such as Rydberg atoms or trapped ions.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.014308}, author = {Verdel, Roberto and Liu, Fangli and Whitsitt, Seth and Gorshkov, V, Alexey and Heyl, Markus} } @article { ISI:000527910200017, title = {Reflection and Time Reversal Symmetry Enriched Topological Phases of Matter: Path Integrals, Non-orientable Manifolds, and Anomalies}, journal = {Commun. Math. Phys.}, volume = {374}, number = {2}, year = {2020}, month = {MAR}, pages = {1021-1124}, publisher = {SPRINGER}, type = {Article}, abstract = {We study symmetry-enriched topological (SET) phases in 2+1 space-time dimensions with spatial reflection and/or time-reversal symmetries. We provide a systematic construction of a wide class of reflection and time-reversal SET phases in terms of a topological path integral defined on general space-time manifolds. An important distinguishing feature of different topological phases with reflection and/or time-reversal symmetry is the value of the path integral on non-orientable space-time manifolds. We derive a simple general formula for the path integral on the manifold Sigma(2) x S-1, where Sigma(2) is a two-dimensional non-orientable surface and S-1 is a circle. This also gives an expression for the ground state degeneracy of the SET on the surface Sigma(2) that depends on the reflection symmetry fractionalization class, generalizing the Verlinde formula for ground state degeneracy on orientable surfaces. Consistency of the action of the mapping class group on non-orientable manifolds leads us to a constraint that can detect when a time-reversal or reflection SET phase is anomalous in (2+1)D and, thus, can only exist at the surface of a (3+1)D symmetry protected topological (SPT) state. Given a (2+1)D reflection and/or time-reversal SET phase, we further derive a general formula that determines which (3+1)D reflection and/or time-reversal SPT phase hosts the (2+1)D SET phase as its surface termination. A number of explicit examples are studied in detail.}, issn = {0010-3616}, doi = {10.1007/s00220-019-03475-8}, author = {Barkeshli, Maissam and Bonderson, Parsa and Cheng, Meng and Jian, Chao-Ming and Walker, Kevin} } @article {barkeshli_relative_2020, title = {Relative anomalies in (2+1){D} symmetry enriched topological states}, journal = {SciPost Phys.}, volume = {8}, number = {2}, year = {2020}, note = {Place: C/O J S CAUX, INST PHYSICS, UNIV AMSTERDAM, AMSTERDAM, 1098 XH, NETHERLANDS Publisher: SCIPOST FOUNDATION Type: Article}, month = {feb}, abstract = {Certain patterns of symmetry fractionalization in topologically ordered phases of matter are anomalous, in the sense that they can only occur at the surface of a higher dimensional symmetry-protected topological (SPT) state. An important question is to determine how to compute this anomaly, which means determining which SPT hosts a given symmetry-enriched topological order at its surface. While special cases are known, a general method to compute the anomaly has so far been lacking. In this paper we propose a general method to compute relative anomalies between different symmetry fractionalization classes of a given (2+1)D topological order. This method applies to all types of symmetry actions, including anyon-permuting symmetries and general space-time reflection symmetries. We demonstrate compatibility of the relative anomaly formula with previous results for diagnosing anomalies for Z(2)(T) space-time reflection symmetry (e.g. where time-reversal squares to the identity) and mixed anomalies for U(1) x Z(2)(T) and U (1) (sic) Z(2)(T) symmetries. We also study a number of additional examples, including cases where space-time reflection symmetries are intertwined in non-trivial ways with unitary symmetries, such as Z(4)(T) and mixed anomalies for Z(2) x Z(2)(T) symmetry, and unitary Z(2) x Z(2) symmetry with non-trivial anyon permutations.}, issn = {2542-4653}, doi = {10.21468/SciPostPhys.8.2.028}, author = {Barkeshli, Maissam and Cheng, Meng} } @article { ISI:000510386300006, title = {Reversible fluxon logic: Topological particles allow ballistic gates along one-dimensional paths}, journal = {Phys. Rev. B}, volume = {101}, number = {1}, year = {2020}, month = {JAN 31}, pages = {014516}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {As we reach the end of Moore{\textquoteright}s law, digital logic uses irreversible logic gates whose energy consumption has been scaled toward a lower limit. Reversible logic gates can provide a dramatic energy-efficient alternative, but rely on reversible dynamics. Here, we introduce a set of superconducting reversible gates that are powered alone by the inertia of the digital input states, contrasting existing adiabatic prototypes which are powered by an external adiabatic drive. The classic model of an inertia-powered reversible gate uses ballistic particles which scatter in two dimensions, where the digital state is represented by the particle path. Our ballistic gates use as the bit state the topological charge (polarity) of a fluxon moving along a long Josephson junction (LJJ) such that the particle path is confined to one dimension. The fundamental structures of our reversible fluxon logic (RFL) are one-bit gates which consist of two LJJs connected by a circuit interface that comprises three large-capacitor Josephson junctions (JJs). Numerical simulations show how a fluxon approaching the interface under its own inertia converts its energy to an oscillating evanescent field, from which in turn a new fluxon is generated in the other LJJ. We find that this resonant forward scattering of a fluxon across the interface requires large capacitances of the interface JJs because they enable a conversion between bound-evanescent and traveling fluxon states (without external power). Importantly, depending on the circuit parameters, the new fluxon may have either the original or the inverted polarity, and these two processes constitute the fundamental identity and NOT operations of the logic. Based on these one-bit RFL gates, we design and study a related two-bit RFL gate which shows that fluxons can exhibit conditional polarity change. Energy efficiency is accomplished because only a small fraction of the fluxon energy is transferred to modes other than the intended fluxon. Simulations show that over 97\% of the total fluxon energy is preserved during gate operations, in contrast to irreversible gates where the entire bit energy is consumed in bit switching. To provide insight into these phenomena, we analyze the one-bit gate circuits with a collective-coordinate model which describes the field in each LJJ as a combination of fluxon and mirror antifluxon. This allows us to reduce the many junction circuit (the three interface JJs and the many JJs approximating the LJJs, solved numerically) to that of two coupled degrees of freedom that each represent a particle. The evolution of the reduced model agrees quantitatively with the full circuit simulations and validates the use of the mirror-fluxon ansatz. Parameter tolerances are calculated for the proposed circuits and indicate that RFL gates can be manufactured and tested.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.101.014516}, author = {Wustmann, W. and Osborn, K. D.} } @article {monteiro_search_2020, title = {Search for {Composite} {Dark} {Matter} with {Optically} {Levitated} {Sensors}}, journal = {Phys. Rev. Lett.}, volume = {125}, number = {18}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {oct}, abstract = {Results are reported from a search for a class of composite dark matter models with feeble long-range interactions with normal matter. We search for impulses arising from passing dark matter particles by monitoring the mechanical motion of an optically levitated nanogram mass over the course of several days. Assuming such particles constitute the dominant component of dark matter, this search places upper limits on their interaction with neutrons of a(n) {\textless}= 1.2 x 10(-7) at 95\% confidence for dark matter masses between 1 and 10 TeV and mediator masses m(phi) {\textless}= 0.1 eV. Because of the large enhancement of the cross section for dark matter to coherently scatter from a nanogram mass (similar to 10(29) times that for a single neutron) and the ability to detect momentum transfers as small as similar to 200 MeV/c, these results provide sensitivity to certain classes of composite dark matter models that substantially exceeds existing searches, including those employing kilogram- or ton-scale targets. Extensions of these techniques can enable directionally sensitive searches for a broad class of previously inaccessible heavy dark matter candidates.

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.125.181102}, author = {Monteiro, Fernando and Afek, Gadi and Carney, Daniel and Krnjaic, Gordan and Wang, Jiaxiang and Moore, David C.} } @article {brewer_signal_2020, title = {Signal advance and delay due to an optical phase-sensitive amplifier}, journal = {Opt. Express}, volume = {28}, number = {10}, year = {2020}, note = {Place: 2010 MASSACHUSETTS AVE NW, WASHINGTON, DC 20036 USA Publisher: OPTICAL SOC AMER Type: Article}, month = {may}, pages = {14573{\textendash}14579}, abstract = {Fast and slow light media exploit a steep frequency dependence in their index of refraction in order to advance or delay a modulated signal. Here we observe a qualitatively similar advance and delay from an optical phase-sensitive amplifier (PSA). Unlike in the case of slow and fast light, this effect is due to a redistribution of power between imbalanced signal sidebands, and the advance or delay is dependent on the optical phase of the input. The PSA adds energy and also changes the frequency spectrum of the input. We show that the advances and delays observed in a PSA implemented using four-wave mixing in a warm rubidium vapor are consistent with the expected behavior of an ideal PSA.}, issn = {1094-4087}, doi = {10.1364/OE.392789}, author = {Brewer, Nicholas R. and Li, Tian and Jones, Kevin M. and Lett, Paul D.} } @article { ISI:000548153300005, title = {Signaling and scrambling with strongly long-range interactions}, journal = {Phys. Rev. A}, volume = {102}, number = {1}, year = {2020}, month = {JUL 8}, pages = {010401}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Strongly long-range interacting quantum systems-those with interactions decaying as a power law 1/r(alpha) in the distance r on a D-dimensional lattice for alpha <= D-have received significant interest in recent years. They are present in leading experimental platforms for quantum computation and simulation, as well as in theoretical models of quantum-information scrambling and fast entanglement creation. Since no notion of locality is expected in such systems, a general understanding of their dynamics is lacking. In a step towards rectifying this problem, we prove two Lieb-Robinson-type bounds that constrain the time for signaling and scrambling in strongly long-range interacting systems, for which no tight bounds were previously known. Our first bound applies to systems mappable to free-particle Hamiltonians with long-range hopping, and is saturable for alpha <= D/2. Our second bound pertains to generic long-range interacting spin Hamiltonians and gives a tight lower bound for the signaling time to extensive subsets of the system for all alpha < D. This many-site signaling time lower bounds the scrambling time in strongly long-range interacting systems.}, issn = {1050-2947}, doi = {10.1103/PhysRevA.102.010401}, author = {Guo, Andrew Y. and Tran, Minh C. and Childs, Andrew M. and Gorshkov, V, Alexey and Gong, Zhe-Xuan} } @article {drake_simplify_2020, title = {Simplify your life}, journal = {Nat. Phys.}, volume = {16}, number = {12}, year = {2020}, note = {Place: HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY Publisher: NATURE RESEARCH Type: Editorial Material}, month = {dec}, pages = {1242}, abstract = {Within the Hartree atomic unit systems, the Schrodinger equation becomes parameter free. But there{\textquoteright}s more to it than making a student{\textquoteright}s life easier, as Gordon Drake and Eite Tiesinga recount.}, issn = {1745-2473}, doi = {10.1038/s41567-020-01095-x}, author = {Drake, Gordon W. F. and Tiesinga, Eite} } @conference {sabines-chesterking_single-emitter-sensitivity_2020, title = {Single-emitter-sensitivity in flow cytometry verified by quantum measurement}, booktitle = {Conference on Lasers and Electro-Optics (CLEO)}, series = {Conference on {Lasers} and {Electro}-{Optics}}, year = {2020}, note = {Backup Publisher: IEEE ISSN: 2160-9020 Type: Proceedings Paper}, publisher = {IEEE}, organization = {IEEE}, abstract = {We demonstrate single quantum emitter sensitivity in a flow cytometer by measuring the second order correlation function to be g((2))(0) = 0.5(1). (C) 2020 The Author(s)

}, isbn = {978-1-943580-76-7}, author = {Sabines-Chesterking, Javier and Burenkov, Ivan A. and Polyakov, V, Sergey} } @article { ISI:000531592100001, title = {Single-photon sources: Approaching the ideal through multiplexing}, journal = {Rev. Sci. Instrum.}, volume = {91}, number = {4}, year = {2020}, month = {APR 1}, pages = {041101}, publisher = {AMER INST PHYSICS}, type = {Review}, abstract = {We review the rapid recent progress in single-photon sources based on multiplexing multiple probabilistic photon-creation events. Such multiplexing allows higher single-photon probabilities and lower contamination from higher-order photon states. We study the requirements for multiplexed sources and compare various approaches to multiplexing using different degrees of freedom.}, issn = {0034-6748}, doi = {10.1063/5.0003320}, author = {Meyer-Scott, Evan and Silberhorn, Christine and Migdall, Alan} } @article { ISI:000511450000006, title = {Spatial Coherence of Spin-Orbit-Coupled Bose Gases}, journal = {Phys. Rev. Lett.}, volume = {124}, number = {5}, year = {2020}, month = {FEB 6}, pages = {053605}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Spin-orbit-coupled Bose-Einstein condensates (SOBECs) exhibit two new phases of matter, now known as the stripe and plane-wave phases. When two interacting spin components of a SOBEC spatially overlap, density modulations with periodicity given by the spin-orbit coupling strength appear. In equilibrium, these components fully overlap in the miscible stripe phase and overlap only in a domain wall in the immiscible plane-wave phase. Here we probe the density modulation present in any overlapping region with optical Bragg scattering and observe the sudden drop of Bragg scattering as the overlapping region shrinks. Using an atomic analog of the Talbot effect, we demonstrate the existence of long-range coherence between the different spin components in the stripe phase and surprisingly even in the phase-separated plane-wave phase.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.124.053605}, author = {Putra, Andika and Salces-Carcoba, F. and Yue, Yuchen and Sugawa, Seiji and Spielman, I. B.} } @article {throckmorton_spontaneous_2020, title = {Spontaneous symmetry breaking in a honeycomb lattice subject to a periodic potential}, journal = {Phys. Rev. Res.}, volume = {2}, number = {2}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {may}, abstract = {Motivated by recent developments in twisted bilayer graphene moire superlattices, we investigate the effects of electron-electron interactions in a honeycomb lattice with an applied periodic potential using a finite-temperature Wilson-Fisher momentum shell renormalization group (RG) approach. We start with a low-energy effective theory for such a system, at first giving a discussion of the most general case in which no point group symmetry is preserved by the applied potential, and then focusing on the special case in which the potential preserves a D-3 point group symmetry. As in similar studies of bilayer graphene, we find that, while the coupling constants describing the interactions diverge at or below a certain critical temperature T = T-c, it turns out that ratios of these constants remain finite and in fact provide information about what types of orders the system is becoming unstable to. However, in contrast to these previous studies, we only find isolated fixed rays, indicating that these orders are likely unstable to perturbations to the coupling constants. Our RG analysis leads to the qualitative conclusion that the emergent interaction-induced symmetry-breaking phases in this model system, and perhaps therefore by extension in twisted bilayer graphene, are generically unstable and fragile, and may thus manifest strong sample dependence.}, doi = {10.1103/PhysRevResearch.2.023225}, author = {Throckmorton, Robert E. and Das Sarma, S.} } @conference {moille_stable_2020, title = {Stable {Dissipative} {Kerr} {Solitons} in a {AlGaAs} {Microresonator} {Through} {Cryogenic} {Operation}}, booktitle = {Conference on Lasers and Electro-Optics (CLEO)}, series = {Conference on {Lasers} and {Electro}-{Optics}}, year = {2020}, note = {Backup Publisher: IEEE ISSN: 2160-9020 Type: Proceedings Paper}, publisher = {IEEE}, organization = {IEEE}, abstract = {We demonstrate stable microresonator Kerr solitons in an Al0.2Ga0.8As-on-insulator resonator thanks to cryogenic quenching of the thermorefractive effect. Reaching such a phase-stable state is a prerequisite to fully exploit the potential of this platform. (C) 2020 The Author(s)

}, isbn = {978-1-943580-76-7}, author = {Moille, Gregory and Chang, Lin and Xie, Weiqiang and Lu, Xiyuan and Davanco, Marcelo and Bowers, John E. and Srinivasan, Kartik} } @article { ISI:000533504100003, title = {State-Dependent Optical Lattices for the Strontium Optical Qubit}, journal = {Phys. Rev. Lett.}, volume = {124}, number = {20}, year = {2020}, month = {MAY 18}, pages = {203201}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We demonstrate state-dependent optical lattices for the Sr optical qubit at the tune-out wavelength for its ground state. We tightly trap excited state atoms while suppressing the effect of the lattice on ground state atoms by more than 4 orders of magnitude. This highly independent control over the qubit states removes inelastic excited state collisions as the main obstacle for quantum simulation and computation schemes based on the Sr optical qubit. Our results also reveal large discrepancies in the atomic data used to calibrate the largest systematic effect of Sr optical lattice clocks.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.124.203201}, author = {Heinz, A. and Park, A. J. and Santi, N. and Trautmann, J. and Porsev, S. G. and Safronova, M. S. and Bloch, I and Blatt, S.} } @article {saha_strongly_2020, title = {Strongly interacting spin-orbit coupled {Bose}-{Einstein} condensates in one dimension}, journal = {Phys. Rev. Res.}, volume = {2}, number = {1}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {mar}, abstract = {We theoretically study dilute superfluidity of spin-1 bosons with antiferromagnetic interactions and synthetic spin-orbit coupling (SOC) in a one-dimensional lattice. Employing a combination of density matrix renormalization group and quantum field theoretical techniques we demonstrate the appearance of a robust superfluid spin-liquid phase in which the spin sector of this spinor Bose-Einstein condensate remains quantum disordered even after introducing quadratic Zeeman and helical magnetic fields. Despite remaining disordered, the presence of these symmetry-breaking fields lifts the perfect spin-charge separation and thus the nematic correlators obey power-law behavior. We demonstrate that, at strong coupling, the SOC induces a charge density wave state that is not accessible in the presence of linear and quadratic Zeeman fields alone. In addition, the SOC induces oscillations in the spin and nematic expectation values as well as the bosonic Green{\textquoteright}s function. These nontrivial effects of an SOC are suppressed under the application of a large quadratic Zeeman field. We discuss how our results could be observed in experiments on ultracold gases of Na-23 in an optical lattice.}, doi = {10.1103/PhysRevResearch.2.013252}, author = {Saha, Siddhartha and Konig, E. J. and Lee, Junhyun and Pixley, J. H.} } @article { ISI:000505984100002, title = {Subband occupation in semiconductor-superconductor nanowires}, journal = {Phys. Rev. B}, volume = {101}, number = {4}, year = {2020}, month = {JAN 7}, pages = {045405}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Subband occupancy (i.e., the number of occupied confinement-induced subbands of the semiconductor wire) is a key physical parameter determining the topological properties of superconductor-semiconductor hybrid systems investigated in the context of the search for non-Abelian Majorana zero modes. We theoretically study the subband occupation of semiconductor nanowire devices as a function of the applied gate potential, the semiconductor-superconductor (SM-SC) work function difference, and the surface charge density by solving self-consistently the Schrodinger-Poisson equations for the conduction electrons of the semiconductor nanowire. Realistic surface charge densities, which are responsible for band bending, are shown to significantly increase the number of occupied subbands, making it difficult or impossible to reach a regime where only a few subbands are occupied. We also show that the energy separation between subbands is significantly reduced in the regime of many occupied subbands, with highly detrimental consequences for the realization and observation of robust Majorana zero modes. As a consequence, the requirements for the realization of robust topological superconductivity and Majorana zero modes should include a low value of the chemical potential, consistent with the occupation of only a few subbands. Finally, we show that the local density of states on the exposed nanowire facets provides a powerful tool for identifying a regime with many occupied subbands and is capable of providing additional critical information regarding the feasibility of Majorana physics in semiconductor-superconductor devices. In our work we address both InAs/Al and InSb/Al superconductor-nanowire hybrid systems of current experimental interest.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.101.045405}, author = {Woods, Benjamin D. and Das Sarma, Sankar and Stanescu, Tudor D.} } @article {19026, title = {Symmetry Breaking and Error Correction in Open Quantum Systems}, journal = {Phys. Rev. Lett.}, volume = {125}, year = {2020}, month = {Dec}, pages = {240405}, abstract = {Symmetry-breaking transitions are a well-understood phenomenon of closed quantum systems in quantum optics, condensed matter, and high energy physics. However, symmetry breaking in open systems is less thoroughly understood, in part due to the richer steady-state and symmetry structure that such systems possess. For the prototypical open system{\textemdash}a Lindbladian{\textemdash}a unitary symmetry can be imposed in a {\textquotedblleft}weak{\textquotedblright} or a {\textquotedblleft}strong{\textquotedblright} way. We characterize the possible\ Zn\ symmetry-breaking transitions for both cases. In the case of\ Z2, a weak-symmetry-broken phase guarantees at most a classical bit steady-state structure, while a strong-symmetry-broken phase admits a partially protected steady-state qubit. Viewing photonic cat qubits through the lens of strong-symmetry breaking, we show how to dynamically recover the logical information after any gap-preserving strong-symmetric error; such recovery becomes perfect exponentially quickly in the number of photons. Our study forges a connection between driven-dissipative phase transitions and error correction.

}, doi = {10.1103/PhysRevLett.125.240405}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.125.240405}, author = {Lieu, Simon and Belyansky, Ron and Young, Jeremy T. and Lundgren, Rex and Albert, Victor V. and Gorshkov, Alexey V.} } @article {wu_three-dimensional_2020, title = {Three-dimensional topological twistronics}, journal = {Phys. Rev. Res.}, volume = {2}, number = {2}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {apr}, abstract = {We introduce a theoretical framework for the concept of three-dimensional (3D) twistronics by developing a generalized Bloch band theory for 3D layered systems with a constant twist angle theta between successive layers. Our theory employs a nonsymmorphic symmetry that enables a precise definition of an effective out-of-plane crystal momentum, and also captures the in-plane moire pattern formed between neighboring twisted layers. To demonstrate topological physics that can be achieved through 3D twistronics, we present two examples. In the first example of chiral twisted graphite, Weyl nodes arise because of inversion-symmetry breaking, with theta-tuned transitions between type-I and type-II Weyl fermions, as well as magic angles at which the in-plane velocity vanishes. In the second example of a twisted Weyl semimetal, the twist in the lattice structure induces a chiral gauge field A that has a vortex-antivortex lattice configuration. Line modes bound to the vortex cores of the A field give rise to 3D Weyl physics in the moire scale. We also discuss possible experimental realizations of 3D twistronics.}, doi = {10.1103/PhysRevResearch.2.022010}, author = {Wu, Fengcheng and Zhang, Rui-Xing and Das Sarma, Sankar} } @article { ISI:000521105100002, title = {Time Evolution of Correlation Functions in Quantum Many-Body Systems}, journal = {Phys. Rev. Lett.}, volume = {124}, number = {11}, year = {2020}, month = {MAR 19}, pages = {110605}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We give rigorous analytical results on the temporal behavior of two-point correlation functions-also known as dynamical response functions or Green{\textquoteright}s functions-in closed many-body quantum systems. We show that in a large class of translation-invariant models the correlation functions factorize at late times \< A(t)B \>(beta) -\> \< A \>(beta) \< B \>(beta) , thus proving that dissipation emerges out of the unitary dynamics of the system. We also show that for systems with a generic spectrum the fluctuations around this late-time value are bounded by the purity of the thermal ensemble, which generally decays exponentially with system size. For autocorrelation functions we provide an upper bound on the timescale at which they reach the factorized late time value. Remarkably, this bound is only a function of local expectation values and does not increase with system size. We give numerical examples that show that this bound is a good estimate in nonintegrable models, and argue that the timescale that appears can be understood in terms of an emergent fluctuationdissipation theorem. Our study extends to further classes of two point functions such as the symmetrized ones and the Kubo function that appears in linear response theory, for which we give analogous results.

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.124.110605}, author = {Alhambra, Alvaro M. and Riddell, Jonathon and Garcia-Pintos, Luis Pedro} } @article {nicholson_time-information_2020, title = {Time-information uncertainty relations in thermodynamics}, journal = {Nat. Phys.}, volume = {16}, number = {12}, year = {2020}, note = {Place: HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY Publisher: NATURE RESEARCH Type: Article}, month = {dec}, abstract = {Physical systems powering motion and creating structure in a fixed amount of time dissipate energy and produce entropy. Whether living, synthetic or engineered, systems performing these dynamic functions must balance dissipation and speed. Here, we show that rates of energy and entropy exchange are subject to a speed limit-a time-information uncertainty relation-imposed by the rates of change in the information content of the system. This uncertainty relation bounds the time that elapses before the change in a thermodynamic quantity has the same magnitude as its s.d. From this general bound, we establish a family of speed limits for heat, dissipated/chemical work and entropy depending on the experimental constraints on the system and its environment. In all of these inequalities, the timescale of transient dynamical fluctuations is universally bounded by the Fisher information. Moreover, they all have a mathematical form that mirrors the Mandelstam-Tamm version of the time-energy uncertainty relation in quantum mechanics. These bounds on the speed of arbitrary observables apply to transient systems away from thermodynamic equilibrium, independent of the physical constraints on the stochastic dynamics or their function. A time-information uncertainty relation in thermodynamics has been derived, analogous to the time-energy uncertainty relation in quantum mechanics, imposing limits on the speed of energy and entropy exchange between a system and external reservoirs.}, issn = {1745-2473}, doi = {10.1038/s41567-020-0981-y}, author = {Nicholson, Schuyler B. and Garcia-Pintos, Luis Pedro and del Campo, Adolfo and Green, Jason R.} } @article {17056, title = {Time-Resolving Quantum Measurement Enables Energy-Efficient, Large-Alphabet Communication}, journal = {PRX Quantum}, volume = {1}, year = {2020}, month = {Sep}, pages = {010308}, doi = {10.1103/PRXQuantum.1.010308}, url = {https://link.aps.org/doi/10.1103/PRXQuantum.1.010308}, author = {Burenkov, I.A. and Jabir, M.V. and Battou, A. and Polyakov, S.V.} } @article {vu_time-reversal-invariant_2020, title = {Time-reversal-invariant {C}-2-symmetric higher-order topological superconductors}, journal = {Phys. Rev. Res.}, volume = {2}, number = {4}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {nov}, abstract = {We propose a minimal lattice model for two-dimensional class DIII superconductors with C-2-protected higher-order topology. Although this class of superconductors cannot be topologically characterized by symmetry eigenvalues at high-symmetry momenta, we propose a simple Wannier-orbital-based real-space diagnosis to unambiguously capture the corresponding higher-order topology. We further identify and characterize a variety of conventional topological phases in our minimal model, including a weak topological superconductor and a nodal topological superconductor with chiral-symmetry protection. The disorder effect is also systematically studied to demonstrate the robustness of higher-order bulk-boundary correspondence. Our theory lays the groundwork for predicting and diagnosing C-2-protected higher-order topology in class DIII superconductors.}, doi = {10.1103/PhysRevResearch.2.043223}, author = {Vu, DinhDuy and Zhang, Rui-Xing and Das Sarma, S.} } @article {aasen_topological_2020, title = {Topological defect networks for fractons of all types}, journal = {Phys. Rev. Res.}, volume = {2}, number = {4}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, abstract = {Fracton phases exhibit striking behavior which appears to render them beyond the standard topological quantum field theory (TQFT) paradigm for classifying gapped quantum matter. Here, we explore fracton phases from the perspective of defect TQFTs and show that topological defect networks-networks of topological defects embedded in stratified 3+1-dimensional (3+1D) TQFTs-provide a unified framework for describing various types of gapped fracton phases. In this picture, the subdimensional excitations characteristic of fractonic matter are a consequence of mobility restrictions imposed by the defect network. We conjecture that all gapped phases, including fracton phases, admit a topological defect network description and support this claim by explicitly providing such a construction for many well-known fracton models, including the X-cube and Haah{\textquoteright}s B code. To highlight the generality of our framework, we also provide a defect network construction of a fracton phase hosting non-Abelian fractons. As a byproduct of this construction, we obtain a generalized membrane-net description for fractonic ground states as well as an argument that our conjecture implies no topological fracton phases exist in 2+1-dimensional gapped systems. Our paper also sheds light on techniques for constructing higher-order gapped boundaries of 3+1D TQFTs.}, doi = {10.1103/PhysRevResearch.2.043165}, author = {Aasen, David and Bulmash, Daniel and Prem, Abhinav and Slagle, Kevin and Williamson, Dominic J.} } @article { ISI:000554826100006, title = {Topological superconductivity, ferromagnetism, and valley-polarized phases in moire systems: Renormalization group analysis for twisted double bilayer graphene}, journal = {Phys. Rev. B}, volume = {102}, number = {8}, year = {2020}, month = {AUG 3}, pages = {085103}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Recent experiments have observed possible spin- and valley-polarized insulators and spin-triplet superconductivity in twisted double bilayer graphene, a moire structure consisting of a pair of Bernal-stacked bilayer graphene. Besides the continuously tunable bandwidths controlled by an applied displacement field and twist angle, these moire bands also possess Van Hove singularities near the Fermi surface and a field-dependent nesting which is far from perfect. Here we carry out a perturbative renormalization group analysis to unbiasedly study the competition among all possible instabilities in twisted double bilayer graphene and related systems with a similar Van Hove fermiology in the presence of weak but finite repulsive interactions. Our key finding is that there are several competing magnetic, valley, charge, and superconducting instabilities arising from interactions in twisted double bilayer graphene, which can be tuned by controlling the displacement field and the twist angle. In particular, we show that spin- or valley-polarized uniform instabilities generically dominate under moderate interactions smaller than the bandwidth, whereas p-wave spin-triplet topological superconductivity and exotic spin-singlet modulated paired state become important as the interactions decrease. Realization of our findings in general moire systems with a similar Van Hove fermiology should open up new opportunities for manipulating topological superconductivity and spin- or valley-polarized states in highly tunable platforms.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.085103}, author = {Hsu, Yi-Ting and Wu, Fengcheng and Das Sarma, S.} } @article {16646, title = {Towards analog quantum simulations of lattice gauge theories with trapped ions}, journal = {Phys. Rev. Research}, volume = {2}, year = {2020}, month = {Apr}, pages = {023015}, doi = {10.1103/PhysRevResearch.2.023015}, url = {https://link.aps.org/doi/10.1103/PhysRevResearch.2.023015}, author = {Davoudi, Zohreh and Hafezi, Mohammad and Monroe, Christopher and Pagano, Guido and Seif, Alireza and Shaw, Andrew} } @article {vu_tunneling_2020, title = {Tunneling conductance of long-range {Coulomb} interacting {Luttinger} liquid}, journal = {Phys. Rev. Res.}, volume = {2}, number = {2}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {may}, abstract = {The theoretical model of the short-range interacting Luttinger liquid predicts a power-law scaling of the density of states and the momentum distribution function around the Fermi surface, which can be readily tested through tunneling experiments. However, some physical systems have long-range interaction, most notably the Coulomb interaction, leading to significantly different behaviors from the short-range interacting system. In this paper, we revisit the tunneling theory for the one-dimensional electrons interacting via the long-range Coulomb force. We show that, even though in a small dynamic range of temperature and bias voltage the tunneling conductance may appear to have a power-law decay similar to short-range interacting systems, the effective exponent is scale dependent and slowly increases with decreasing energy. This factor may lead to the sample-to-sample variation in the measured tunneling exponents. We also discuss the crossover to a free Fermi gas at high energy and the effect of the finite size. Our work demonstrates that experimental tunneling measurements in one-dimensional electron systems should be interpreted with great caution when the system is a Coulomb Luttinger liquid.}, doi = {10.1103/PhysRevResearch.2.023246}, author = {Vu, DinhDuy and Iucci, Anibal and Das Sarma, S.} } @article {zhang_twist-angle_2020, title = {Twist-angle dependence of moire excitons in {WS2}/{MoSe2} heterobilayers}, journal = {Nat. Commun.}, volume = {11}, number = {1}, year = {2020}, note = {Place: HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY Publisher: NATURE RESEARCH Type: Article}, month = {nov}, abstract = {Moire lattices formed in twisted van der Waals bilayers provide a unique, tunable platform to realize coupled electron or exciton lattices unavailable before. While twist angle between the bilayer has been shown to be a critical parameter in engineering the moire potential and enabling novel phenomena in electronic moire systems, a systematic experimental study as a function of twist angle is still missing. Here we show that not only are moire excitons robust in bilayers of even large twist angles, but also properties of the moire excitons are dependant on, and controllable by, the moire reciprocal lattice period via twist-angle tuning. From the twist-angle dependence, we furthermore obtain the effective mass of the interlayer excitons and the electron inter-layer tunneling strength, which are difficult to measure experimentally otherwise. These findings pave the way for understanding and engineering rich moire-lattice induced phenomena in angle-twisted semiconductor van der Waals heterostructures. Here, the authors show that the properties of the moire excitons in twisted van der Waals bilayers of transition metal dichalcogenides are determined by the moire reciprocal lattice period, and can be controlled via twist-angle tuning.}, issn = {2041-1723}, doi = {10.1038/s41467-020-19466-6}, author = {Zhang, Long and Zhang, Zhe and Wu, Fengcheng and Wang, Danqing and Gogna, Rahul and Hou, Shaocong and Watanabe, Kenji and Taniguchi, Takashi and Kulkarni, Krishnamurthy and Kuo, Thomas and Forrest, Stephen R. and Deng, Hui} } @article {bienias_two_2020, title = {Two photon conditional phase gate based on {Rydberg} slow light polaritons}, journal = {J. Phys. B-At. Mol. Opt. Phys.}, volume = {53}, number = {5}, year = {2020}, note = {Place: TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND Publisher: IOP PUBLISHING LTD Type: Article}, month = {mar}, abstract = {We analyze the fidelity of a deterministic quantum phase gate (QPG) for two photons counterpropagating as polaritons through a cloud of Rydberg atoms under the condition of electromagnetically induced transparency (EIT). We provide analytical results for the phase shift of the quantum gate, and provide an estimation for all processes leading to a reduction to the gate fidelity. Especially, the influence of losses from the intermediate level, dispersion of the photon wave packet, scattering into additional polariton channels, finite lifetime of the Rydberg state, as well as effects of transverse size of the wave packets are accounted for. We show that the flatness of the effective interaction, caused by the blockade phenomena, suppresses the corrections due to the finite transversal size. This is a strength of Rydberg-EIT setup compared to other approaches. Finally, we provide the experimental requirements for the realization of a high fidelity QPG using Rydberg polaritons.}, keywords = {amo, quantum gate, Quantum optics, Rydberg polaritons, Rydbergs}, issn = {0953-4075}, doi = {10.1088/1361-6455/ab5bed}, author = {Bienias, Przemyslaw and Buechler, Hans Peter} } @article { ISI:000562002100002, title = {Two-dimensional electron self-energy: Long-range Coulomb interaction}, journal = {Phys. Rev. B}, volume = {102}, number = {8}, year = {2020}, month = {AUG 24}, pages = {085145}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The electron self-energy for long-range Coulomb interactions plays a crucial role in understanding the many-body physics of interacting electron systems (e.g., in metals and semiconductors) and has been studied extensively for decades. In fact, it is among the oldest and the most-investigated many-body problems in physics. However, there is a lack of an analytical expression for the self-energy Re Sigma((R)) (epsilon, T) when energy epsilon and temperature k(B)T are arbitrary with respect to each other (while both being still small compared with the Fermi energy). We revisit this problem and calculate analytically the self-energy on the mass shell for a two-dimensional electron system with Coulomb interactions in the high density limit r(s)<< 1, for temperature r(s)(3/2) << k(B)T/E-F << r(s) and energy r(s)(3/2) << vertical bar epsilon vertical bar << r(s). We provide the exact high-density analytical expressions for the real and imaginary parts of the electron self-energy with arbitrary value of epsilon/KBT, to the leading order in the dimensionless Coulomb coupling constant r(s), and to several higher than leading orders in k(B)T/r(s)E(F) and epsilon/r(s)E(F) . We also obtain the asymptotic behavior of the self-energy in the regimes vertical bar epsilon vertical bar << k(B)T and vertical bar epsilon vertical bar >> k(B)T. The higher-order terms have subtle and highly nontrivial compound logarithmic contributions from both epsilon and T, explaining why they have never before been calculated in spite of the importance of the subject matter.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.085145}, author = {Liao, Yunxiang and Buterakos, Donovan and Schecter, Mike and Das Sarma, Sankar} } @article { ISI:000515320000001, title = {Type II Photoinitiator and Tuneable Poly(Ethylene Glycol)-Based Materials Library for Visible Light Photolithography}, journal = {Tissue Eng. Part A}, volume = {26}, number = {5-6}, year = {2020}, month = {MAR 1}, pages = {292-304}, publisher = {MARY ANN LIEBERT, INC}, type = {Article}, abstract = {Stereolithography (SL) has several advantages over traditional biomanufacturing techniques such as fused deposition modeling, including increased speed, accuracy, and efficiency. While SL has been broadly used in tissue engineering for the fabrication of three-dimensional scaffolds that can mimic the in vivo environment for cell growth and tissue regeneration, lithographic printing is usually performed on single-component materials cured with ultraviolet light, severely limiting the versatility and cytocompatibility of such systems. In this study, we report a highly tunable, low-cost photoinitiator system that we used to establish a systematic library of crosslinked materials based on low molecular weight poly(ethylene glycol) diacrylate. We assessed the physicochemical properties, photocrosslinking efficiency, cost performance, and biocompatibility to demonstrate the capability of manufacturing a multimaterial complex tissue scaffold.

}, keywords = {bioink, multimaterial scaffold, photocrosslinkable hydrogel, poly(ethylene glycol) diacrylate (PEG-DA), stereolithography, visible light type II photoinitiator}, issn = {1937-3341}, doi = {10.1089/ten.tea.2019.0282},}, author = {Yang, Xin and Mohseni, Mina and Bas, Onur and Meinert, Christoph and New, Elizabeth J. and Castro, Nathan J.} } @article { ISI:000560967100009, title = {Unitary Subharmonic Response and Floquet Majorana Modes}, journal = {Phys. Rev. Lett.}, volume = {125}, number = {8}, year = {2020}, month = {AUG 20}, pages = {086804}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Detection and manipulation of excitations with non-Abelian statistics, such as Majorana fermions, are essential for creating topological quantum computers. To this end, we show the connection between the existence of such localized particles and the phenomenon of unitary subharmonic response (SR) in periodically driven systems. In particular, starting from highly nonequilibrium initial states, the unpaired Majorana modes exhibit spin oscillations with twice the driving period, are localized, and can have exponentially long lifetimes in clean systems. While the lifetime of SR is limited in translationally invariant systems, we show that disorder can be engineered to stabilize the subharmonic response of Majorana modes. A viable observation of this phenomenon can be achieved using modern multiqubit hardware, such as superconducting circuits and cold atomic systems.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.125.086804}, author = {Shtanko, Oles and Movassagh, Ramis} } @article {lu_universal_2020, title = {Universal frequency engineering tool for microcavity nonlinear optics: multiple selective mode splitting of whispering-gallery resonances}, journal = {Photonics Res.}, volume = {8}, number = {11}, year = {2020}, note = {Place: PO BOX 800-211, SHANGHAI, 201800, PEOPLES R CHINA Publisher: CHINESE LASER PRESS Type: Article}, month = {nov}, pages = {1676{\textendash}1686}, abstract = {Whispering-gallery microcavities have been used to realize a variety of efficient parametric nonlinear optical processes through the enhanced light-matter interaction brought about by supporting multiple high quality factor and small modal volume resonances. Critical to such studies is the ability to control the relative frequencies of the cavity modes, so that frequency matching is achieved to satisfy energy conservation. Typically this is done by tailoring the resonator cross section. Doing so modifies the frequencies of all of the cavity modes, that is, the global dispersion profile, which may be undesired, for example, in introducing competing nonlinear processes. Here, we demonstrate a frequency engineering tool, termed multiple selective mode splitting (MSMS), that is independent of the global dispersion and instead allows targeted and independent control of the frequencies of multiple cavity modes. In particular, we show controllable frequency shifts up to 0.8 nm, independent control of the splitting of up to five cavity modes with optical quality factors {\textgreater}= 10(5), and strongly suppressed frequency shifts for untargeted modes. The MSMS technique can be broadly applied to a wide variety of nonlinear optical processes across different material platforms and can be used to both selectively enhance processes of interest and suppress competing unwanted processes.}, issn = {2327-9125}, doi = {10.1364/PRJ.401755}, author = {Lu, Xiyuan and Rao, Ashutosh and Moille, Gregory and Westly, Daron A. and Srinivasan, Kartik} } @article {16951, title = {Universal Logical Gates on Topologically Encoded Qubits via Constant-Depth Unitary Circuits}, journal = {Phys. Rev. Lett.}, volume = {125}, year = {2020}, month = {Jul}, pages = {050502}, doi = {10.1103/PhysRevLett.125.050502}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.125.050502}, author = {Zhu, Guanyu and Lavasani, Ali and Barkeshli, Maissam} } @article { ISI:000563710400004, title = {Universal nonequilibrium I-V curve near the two-channel Kondo-Luttinger quantum critical point}, journal = {Phys. Rev. B}, volume = {102}, number = {7}, year = {2020}, month = {AUG 28}, pages = {075145}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Over recent decades, a growing number of systems, many of them quantum critical, have been shown to exhibit non-Fermi-liquid behavior, but a full analytic understanding of such systems out of equilibrium is still lacking. In this paper, we provide a distinct example with broad applications in correlated mesoscopic systems to two-channel Kondo-Luttinger model where a Kondo impurity couples to two voltage-biased interacting electron leads, experimentally realizable in a dissipative quantum dot. Therein, an exotic quantum phase transition has been known to exist since the 1990s from the one-channel to two-channel Kondo ground states by enhancing electron interactions in the leads, but a controlled analytic approach to this quantum critical point has not yet been established due to the breakdown of weak-coupling perturbation theory near this strong-coupling critical point. We present a controlled method to this long-standing problem by mapping the system in the strong-coupling regime to an effective spin-boson-fermion Hamiltonian. Another type of non-Fermi-liquid quantum critical point is discovered with a distinct logarithmic-in-temperature and -voltage dependence in transport. We further obtain an analytical form for the universal differential conductance out of equilibrium near the transition. Our approach can be further generalized to study nonequilibrium physics of other strong-coupling low-dimensional non-Fermi-liquid fixed points. The relevance of our results for recent experiments is discussed.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.075145}, author = {Lin, C-Y and Chang, Y-Y and Rylands, C. and Andrei, N. and Chung, C-H} } @article { ISI:000558086800008, title = {Viscous Properties of a Degenerate One-Dimensional Fermi Gas}, journal = {Phys. Rev. Lett.}, volume = {125}, number = {7}, year = {2020}, month = {AUG 11}, pages = {076601}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study the viscous properties of a system of weakly interacting spin-1/2 fermions in one dimension. Accounting for the effect of interactions on the quasiparticle energy spectrum, we obtain the bulk viscosity of this system at low temperatures. Our result is valid for frequencies that are small compared with the rate of fermion backscattering. For frequencies larger than this exponentially small rate, the excitations of the system become decoupled from the center of mass motion, and the fluid is described by two-fluid hydrodynamics. We calculate the three transport coefficients required to describe viscous dissipation in this regime.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.125.076601}, author = {DeGottardi, Wade and Matveev, K. A.} } @article {balram_zn_2020, title = {Z(n) superconductivity of composite bosons and the 7/3 fractional quantum {Hall} effect}, journal = {Phys. Rev. Res.}, volume = {2}, number = {1}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {mar}, abstract = {The topological p-wave pairing of composite fermions, believed to be responsible for the 5/2 fractional quantum Hall effect (FQHE), has generated much exciting physics. Motivated by the parton theory of the FQHE, we consider the possibility of a new kind of emergent {\textquotedblleft}superconductivity{\textquotedblright} in the 1/3 FQHE, which involves condensation of clusters of n composite bosons. From a microscopic perspective, the state is described by the n (n) over bar 111 parton wave function P-LLL Phi(n)Phi(n)*Phi(3)(1), where Phi(n) is the wave function of the integer quantum Hall state with n filled Landau levels and P-LLL is the lowest-Landau-level projection operator. It represents a Z(n) superconductor of composite bosons, because the factor Phi(3)(1) similar to Pi(j{\textless}k) (z(j) - z(k))(3), where z(j) = x(j) - iy(j) is the coordinate of the jth electron, binds three vortices to electrons to convert them into composite bosons, which then condense into the Z(n) superconducting state vertical bar Phi(n)vertical bar(2). From a field theoretical perspective, this state can be understood by starting with the usual Laughlin theory and gauging a Z(n) subgroup of the U(1) charge conservation symmetry. We find from detailed quantitative calculations that the 2{\textless}(2)over bar{\textgreater}111 and 3 (3) over bar 111 states are at least as plausible as the Laughlin wave function for the exact Coulomb ground state at filling nu = 7/3, suggesting that this physics is possibly relevant for the 7/3 FQHE. The Z(n) order leads to several observable consequences, including quasiparticles with fractionally quantized charges of magnitude e/(3n) and the existence of multiple neutral collective modes. It is interesting that the FQHE may be a promising venue for the realization of exotic Z(n) superconductivity.}, doi = {10.1103/PhysRevResearch.2.013349}, author = {Balram, Ajit C. and Jain, J. K. and Barkeshli, Maissam} } @article { ISI:000501768100003, title = {Additive biomanufacturing of scaffolds for breast reconstruction}, journal = {Addit. Manuf.}, volume = {30}, year = {2019}, month = {DEC}, pages = {UNSP 100845}, publisher = {ELSEVIER}, type = {Article}, abstract = {Limitations for the current clinical treatment strategies for breast reconstruction have prompted researchers and bioengineers to develop unique techniques based on tissue engineering and regenerative medicine (TE\&RM) principles. Recently, scaffold-guided soft TE has emerged as a promising approach due to its potential to modulate the process of tissue regeneration. Herein, we utilized additive biomanufacturing (ABM) to develop an original design-based concept for scaffolds which can be applied in TE-based breast reconstruction procedures. The scaffold design addresses biomechanical and biological requirements for medium to large-volume regeneration with the potential of customization. The model is composed of two independent structural components. The external structure provides biomechanical stability to minimize load transduction to the newly formed tissue while the internal structure provides a large pore and fully interconnected pore architecture to facilitate tissue regeneration. A methodology was established to design, optimize and 3D print the external structure with customized biomechanical properties. The internal structure was also designed and printed with a gradient of pore size and a channel structure to facilitate lipoaspirated fat delivery and entrapment. A fused filament fabrication-based printing strategy was employed to print two structures as a monolithic breast implant.}, keywords = {Additive biomanufacturing, Breast implant customization, In silico modelling, Scaffolds}, issn = {2214-8604}, doi = {10.1016/j.addma.2019.100845}, author = {Mohseni, Mina and Bas, Onur and Castro, Nathan J. and Schmutz, Beat and Hutmacher, Dietmar W.} } @article {13366, title = {Alignment-dependent decay rate of an atomic dipole near an optical nanofiber}, journal = {Phys. Rev. A}, volume = {99}, year = {2019}, month = {Jan}, pages = {013822}, doi = {10.1103/PhysRevA.99.013822}, url = {https://link.aps.org/doi/10.1103/PhysRevA.99.013822}, author = {Solano, P. and Grover, J. A. and Xu, Y. and Barberis-Blostein, P. and Munday, J. N. and Orozco, L. A. and Phillips, W. D. and Rolston, S. L.} } @article {ISI:000480388400001, title = {Almost linear Haldane pseudopotentials and emergent conformal block wave functions in a Landau level}, journal = {Phys. Rev. B}, volume = {100}, number = {7}, year = {2019}, month = {AUG 12}, pages = {075122}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We consider a two-dimensional model of particles interacting in a Landau level. We work in a finite disk geometry and take the particles to interact with a linearly decreasing two-body Haldane pseudopotential. We show that the ground-state subspace of this model is spanned by the wave functions that can be written as polynomial conformal blocks (of an arbitrary conformal field theory) consistent with the filling fraction (scaling dimension). To remove degeneracies, we then add a quadratic perturbation to the Hamiltonian and show that (1) conformal blocks constructed using the Moore-Read construction (e.g., Laughlin, Pfaffian, and Read-Rezayi states) remain exact eigenstates of this model in the thermodynamic limit, and (2) by tuning an externally imposed single-body -L-z(2) potential we can enforce Moore-Read conformal blocks to become exact ground states of this model in the thermodynamic limit. We cannot rule out the possibility of residual degeneracies in this limit. This model has no filling dependence and is comprised only from two-body long-range interactions and external single-body potentials. Our results provide insight into how conformal block wave functions can emerge in a Landau level.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.100.075122}, author = {Alavirad, Yahya} } @article {ISI:000457706700026, title = {Anomalous Low-Temperature Enhancement of Supercurrent in Topological-Insulator Nanoribbon Josephson Junctions: Evidence for Low-Energy Andreev Bound States}, journal = {Phys. Rev. Lett.}, volume = {122}, number = {4}, year = {2019}, month = {FEB 1}, pages = {047003}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We report anomalous enhancement of the critical current at low temperatures in gate-tunable Josephson junctions made from topological insulator BiSbTeSe2 nanoribbons with superconducting Nb electrodes. In contrast to conventional junctions, as a function of the decreasing temperature T, the increasing critical current I-c exhibits a sharp upturn at a temperature T-{*} around 20\% of the junction critical temperature for several different samples and various gate voltages. The I-c vs T demonstrates a short junction behavior for T > T-{*}, but crosses over to a long junction behavior for T < T-{*} with an exponential T dependence I-c proportional to exp(-k(B)T/delta), where k(B) is the Boltzmann constant. The extracted characteristic energy scale delta is found to be an order of magnitude smaller than the induced superconducting gap of the junction. We attribute the long-junction behavior with such a small delta to low-energy Andreev bound states arising from winding of the electronic wave function around the circumference of the topological insulator nanoribbon.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.122.047003}, author = {Kayyalha, Morteza and Kargarian, Mehdi and Kazakov, Aleksandr and Miotkowski, Ireneusz and Galitski, Victor M. and Yakovenko, Victor M. and Rokhinson, Leonid P. and Chen, Yong P.} } @article { ISI:000454906800010, title = {Artificial gauge fields with ultracold atoms}, journal = {PHYSICS TODAY}, volume = {72}, number = {1}, year = {2019}, month = {JAN}, pages = {39-44}, issn = {0031-9228}, doi = {10.1063/PT.3.4111}, author = {Galitski, Victor and Juzeliunas, Gediminas and Ian B Spielman} } @article { ISI:000488203600027, title = {Atypical quantized resistances in millimeter-scale epitaxial graphene p-n junctions}, journal = {Carbon}, volume = {154}, year = {2019}, month = {DEC}, pages = {230-237}, publisher = {PERGAMON-ELSEVIER SCIENCE LTD}, type = {Article}, abstract = {We have demonstrated the millimeter-scale fabrication of monolayer epitaxial graphene p-n junction devices using simple ultraviolet photolithography, thereby significantly reducing device processing time compared to that of electron beam lithography typically used for obtaining sharp junctions. This work presents measurements yielding nonconventional, fractional multiples of the typical quantized Hall resistance at nu = 2 (R-H approximate to 12906 Omega) that take the form: a/bR(H). Here, a and b have been observed to take on values such 1, 2, 3, and 5 to form various coefficients of R-H. Additionally, we provide a framework for exploring future device configurations using the LTspice circuit simulator as a guide to understand the abundance of available fractions one may be able to measure. These results support the potential for drastically simplifying device processing time and may be used for many other two-dimensional materials. Published by Elsevier Ltd.}, issn = {0008-6223}, doi = {10.1016/j.carbon.2019.08.002}, author = {Rigosi, Albert E. and Patel, Dinesh and Marzano, Martina and Kruskopf, Mattias and Hill, Heather M. and Jin, Hanbyul and Hu, Jiuning and Walker, Angela R. Hight and Ortolano, Massimo and Callegaro, Luca and Liang, Chi-Te and Newell, David B.} } @conference {ISI:000482088000005, title = {Auger recombination-induced neutralization and stretched exponential recharging in an InAs quantum dot}, booktitle = {QUANTUM DOTS AND NANOSTRUCTURES: GROWTH, CHARACTERIZATION, AND MODELING XVI}, series = {Proceedings of SPIE}, volume = {10929}, year = {2019}, note = {Conference on Quantum Dots and Nanostructures: Growth, Characterization, and Modeling XVI, San Francisco, CA, FEB 06-07, 2019}, pages = {109290F}, publisher = {SPIE}, organization = {SPIE}, type = {Proceedings Paper}, abstract = {We investigate the charging dynamics in epitaxially grown InAs quantum dots (QDs) under resonant excitation with and without additional low-power above-band excitation. Time-resolved resonance fluorescence from a charged exciton (trion) transition is recorded as the above-band excitation is modulated on and off. The fluorescence intensity varies as the QD changes from charged to neutral and back due to the influence of the above-band excitation. We fit the transients of the decay of the time-resolved resonance fluorescence after the above-band excitation turns off with a model that represents the neutralization process. The time dependence of the transients indicate that Auger recombination of resonantly excited trions is largely responsible for neutralization of the charged state when the above-band excitation is off. Additionally, a stretched exponential component of the transient of the fluorescence decay indicates the QD is supplied with charges via carrier migration through a stochastic collection of weakly-binding sites, resulting in sub-diffusion-like dynamics.}, keywords = {anomalous diffusion, Auger recombination, charge carrier dynamics, quantum dot, resonance fluorescence, stretched exponential, time-resolved, trion}, isbn = {978-1-5106-2501-3}, issn = {0277-786X}, doi = {10.1117/12.2506555}, author = {Lander, Gary R. and Isaac, Samantha D. and Chen, Disheng and Demircan, Samet and Solomon, Glenn S. and Flagg, Edward B.}, editor = {Huffaker, DL and Eisele, H} } @article {ISI:000462066300003, title = {Bell{\textquoteright}s inequality, generalized concurrence and entanglement in qubits}, journal = {Int. J. Mod. Phys. A}, volume = {34}, number = {6-7}, year = {2019}, month = {MAR 10}, pages = {1950032}, publisher = {WORLD SCIENTIFIC PUBL CO PTE LTD}, type = {Article}, abstract = {It is well known that the maximal violation of the Bell{\textquoteright}s inequality for a two-qubit system is related to the entanglement formation in terms of a concurrence. However, a generalization of this relation to an n-qubit state has not been found. In this paper, we demonstrate some extensions of the relation between the upper bound of the Bell{\textquoteright}s violation and a generalized concurrence in several n-qubit states. In particular, we show the upper bound of the Bell{\textquoteright}s violation can be expressed as a function of the generalized concurrence, if a state can be expressed in terms of two variables. We apply the relation to the Wen-Plaquette model and show that the topological entanglement entropy can be extracted from the maximal Bell{\textquoteright}s violation.}, keywords = {Bell{\textquoteright}s inequality, entanglement, generalized concurrence, QUBIT}, issn = {0217-751X}, doi = {10.1142/S0217751X19500325}, author = {Chang, Po-Yao and Chu, Su-Kuan and Ma, Chen-Te} } @article { ISI:000500475200001, title = {Benchmarking an 11-qubit quantum computer}, journal = {Nat. Commun.}, volume = {10}, year = {2019}, month = {NOV 29}, pages = {5464}, publisher = {NATURE PUBLISHING GROUP}, type = {Article}, abstract = {The field of quantum computing has grown from concept to demonstration devices over the past 20 years. Universal quantum computing offers efficiency in approaching problems of scientific and commercial interest, such as factoring large numbers, searching databases, simulating intractable models from quantum physics, and optimizing complex cost functions. Here, we present an 11-qubit fully-connected, programmable quantum computer in a trapped ion system composed of 13 Yb-171(+) ions. We demonstrate average single-qubit gate fidelities of 99.5\%, average two-qubit-gate fidelities of 97.5\%, and SPAM errors of 0.7\%. To illustrate the capabilities of this universal platform and provide a basis for comparison with similarly-sized devices, we compile the Bernstein-Vazirani and Hidden Shift algorithms into our native gates and execute them on the hardware with average success rates of 78\% and 35\%, respectively. These algorithms serve as excellent benchmarks for any type of quantum hardware, and show that our system outperforms all other currently available hardware.}, issn = {2041-1723}, doi = {10.1038/s41467-019-13534-2}, author = {Wright, K. and Beck, K. M. and Debnath, S. and Amini, J. M. and Nam, Y. and Grzesiak, N. and Chen, J. -S. and Pisenti, N. C. and Chmielewski, M. and Collins, C. and Hudek, K. M. and Mizrahi, J. and Wong-Campos, J. D. and Allen, S. and Apisdorf, J. and Solomon, P. and Williams, M. and Ducore, A. M. and Blinov, A. and Kreikemeier, S. M. and Chaplin, V. and Keesan, M. and Monroe, C. and Kim, J.} } @article {ISI:000461964300002, title = {Braiding and gapped boundaries in fracton topological phases}, journal = {Phys. Rev. B}, volume = {99}, number = {12}, year = {2019}, month = {MAR 19}, pages = {125132}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study gapped boundaries of Abelian type-I fracton systems in three spatial dimensions. Using the X-cube model as our motivating example, we give a conjecture, with partial proof, of the conditions for a boundary to be gapped. In order to state our conjecture, we use a precise definition of fracton braiding and show that bulk braiding of fractons has several features that make it insufficient to classify gapped boundaries. Most notable among these is that bulk braiding is sensitive to geometry and is {\textquoteleft}{\textquoteleft}nonreciprocal{{\textquoteright}{\textquoteright}}; that is, braiding an excitation a around b need not yield the same phase as braiding b around a. Instead, we define fractonic {\textquoteleft}{\textquoteleft}boundary braiding,{{\textquoteright}{\textquoteright}} which resolves these difficulties in the presence of a boundary. We then conjecture that a boundary of an Abelian fracton system is gapped if and only if a {\textquoteleft}{\textquoteleft}boundary Lagrangian subgroup{{\textquoteright}{\textquoteright}} of excitations is condensed at the boundary; this is a generalization of the condition for a gapped boundary in two spatial dimensions, but it relies on boundary braiding instead of bulk braiding. We also discuss the distinctness of gapped boundaries and transitions between different topological orders on gapped boundaries.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.125132}, author = {Bulmash, Daniel and Iadecola, Thomas} } @conference {ISI:000482226303019, title = {Bright Beams of Intensity Difference Squeezed Light for use in Sub-shot-noise Imaging}, booktitle = {2019 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO)}, series = {Conference on Lasers and Electro-Optics}, year = {2019}, note = {Conference on Lasers and Electro-Optics (CLEO), San Jose, CA, MAY 05-10, 2019}, publisher = {IEEE; AdValue Photon; Amer Elements; Class5 Photon; Coherent; GoFoton; Light Convers; LightTrans; MKS; OZ Opt Online; Santec; ThorLabs; UQDevices; YSL Photon}, organization = {IEEE; AdValue Photon; Amer Elements; Class5 Photon; Coherent; GoFoton; Light Convers; LightTrans; MKS; OZ Opt Online; Santec; ThorLabs; UQDevices; YSL Photon}, type = {Proceedings Paper}, abstract = {We present a method for using bright beams of intensity difference squeezed light to perform sub-shot-noise imaging. The intensity correlated twin beams are generated by four wave mixing in rubidium vapour. (C) 2019 The Author(s)}, isbn = {978-1-943580-57-6}, issn = {2160-9020}, author = {Speirs, Rory W. and Brewer, Nicholas R. and Wu, Meng-Chang and Lett, Paul D.} } @article { ISI:000488503500029, title = {Broadband resonator-waveguide coupling for efficient extraction of octave-spanning microcombs}, journal = {Opt. Lett.}, volume = {44}, number = {19}, year = {2019}, month = {OCT 1}, pages = {4737-4740}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {Octave-spanning frequency combs have been successfully demonstrated in Kerr nonlinear microresonators. These microcombs rely on both engineered dispersion, to enable generation of frequency components across the octave, and on engineered coupling, to efficiently extract the generated light into an access waveguide while maintaining a close to critically coupled pump. The latter is challenging, as the spatial overlap between the access waveguide and the ring modes decays with frequency. This leads to strong coupling variation across the octave, with poor extraction at short wavelengths. Here, we investigate how a waveguide wrapped around a portion of the resonator, in a pulley scheme, can improve the extraction of octave-spanning microcombs, in particular at short wavelengths. We use the coupled-mode theory to predict the performance of the pulley couplers and demonstrate good agreement with experimental measurements. Using an optimal pulley coupling design, we demonstrate a 20 dB improvement in extraction at short wavelengths compared to straight waveguide coupling. (C) 2019 Optical Society of America}, issn = {0146-9592}, doi = {10.1364/OL.44.004737}, author = {Moille, Gregory and Li, Qing and Briles, Travis C. and Yu, Su-Peng and Drake, Tara and Lu, Xiyuan and Rao, Ashutosh and Westly, Daron and Papp, Scott B. and Srinivasan, Kartik} } @article {ISI:000473123700004, title = {Canonical forms for single-qutrit Clifford plus T operators}, journal = {Ann. Phys.}, volume = {406}, year = {2019}, month = {JUL}, pages = {54-70}, publisher = {ACADEMIC PRESS INC ELSEVIER SCIENCE}, type = {Article}, abstract = {We introduce canonical forms for single qutrit Clifford+T circuits and prove that every single-qutrit Clifford+T operator admits a unique such canonical form. We show that our canonical forms are T-optimal in the sense that among all the single-qutrit Clifford+T circuits implementing a given operator our canonical form uses the least number of T gates. Finally, we provide an algorithm which inputs the description of an operator (as a matrix or a circuit) and constructs the canonical form for this operator. The algorithm runs in time linear in the number of T gates. Our results provide a higher-dimensional generalization of prior work by Matsumoto and Amano who introduced similar canonical forms for single-qubit Clifford+T circuits. (C) 2019 Elsevier Inc. All rights reserved.}, keywords = {Quantum circuits, quantum computation, Qutrits, Universal gate sets}, issn = {0003-4916}, doi = {10.1016/j.aop.2019.04.001}, author = {Glaudell, Andrew N. and Ross, Neil J. and Taylor, Jacob M.} } @article {ISI:000466441100011, title = {Cavity Quantum Eliashberg Enhancement of Superconductivity}, journal = {Phys. Rev. Lett.}, volume = {122}, number = {16}, year = {2019}, month = {APR 26}, pages = {167002}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Driving a conventional superconductor with an appropriately tuned classical electromagnetic field can lead to an enhancement of superconductivity via a redistribution of the quasiparticles into a more favorable nonequilibrium distribution-a phenomenon known as the Eliashberg effect. Here, we theoretically consider coupling a two-dimensional superconducting film to the quantized electromagnetic modes of a microwave resonator cavity. As in the classical Eliashberg case, we use a kinetic equation to study the effect of the fluctuating, dynamical electromagnetic field on the Bogoliubov quasiparticles. We find that when the photon and quasiparticle systems are out of thermal equilibrium, a redistribution of quasiparticles into a more favorable nonequilibrium steady state occurs, thereby enhancing superconductivity in the sample. We predict that by tailoring the cavity environment (e.g., the photon occupation and spectral functions), enhancement can be observed in a variety of parameter regimes, offering a large degree of tunability.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.122.167002}, author = {Curtis, Jonathan B. and Raines, Zachary M. and Allocca, Andrew A. and Hafezi, Mohammad and Galitski, Victor M.} } @article {ISI:000455821100001, title = {Cavity superconductor-polaritons}, journal = {Phys. Rev. B}, volume = {99}, number = {2}, year = {2019}, month = {JAN 14}, pages = {020504}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Following the recent success of realizing exciton-polariton condensates in cavities, we examine the hybridization of cavity photons with the closest analog of excitons within a superconductor, states called Bardasis-Schrieffer modes. Although these modes do not typically couple linearly to light, one can engineer a coupling with an externally imposed supercurrent, leading to the formation of hybridized Bardasis-Schrieffer-polariton states, which we obtain both as poles of the bosonic Green{\textquoteright}s function and through the derivation of an effective Hamiltonian picture for the model. These new excitations have nontrivial overlap with both the original photon states and d-wave superconducting fluctuations. We conjecture that a phase-coherent density of these objects could produce a finite d-wave component of the superconducting order parameter-an s +/- id superconducting state.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.020504}, author = {Allocca, Andrew A. and Raines, Zachary M. and Curtis, Jonathan B. and Galitski, Victor M.} } @article {ISI:000476652500107, title = {Chiral light-matter interactions using spin-valley states in transition metal dichalcogenides}, journal = {Opt. Express}, volume = {27}, number = {15}, year = {2019}, month = {JUL 22}, pages = {21367-21379}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {Chiral light-matter interactions can enable polarization to control the direction of light emission in a photonic device. Most realizations of chiral light-matter interactions require external magnetic fields to break time-reversal symmetry of the emitter. One way to eliminate this requirement is to utilize strong spin-orbit coupling present in transition metal dichalcogenides that exhibit a valley-dependent polarized emission. Such interactions were previously reported using plasmonic waveguides, but these structures exhibit short propagation lengths due to loss. Chiral dielectric structures exhibit much lower loss levels and could therefore solve this problem. We demonstrate chiral light-matter interactions using spin-valley states of transition metal dichalcogenide monolayers coupled to a dielectric waveguide. We use a photonic crystal glide-plane waveguide that exhibits chiral modes with high field intensity, coupled to monolayer WSe2. We show that the circularly polarized emission of the monolayer preferentially couples to one direction of the waveguide, with a directionality as high as 0.35, limited by the polarization purity of the bare monolayer emission. This system enables on-chip directional control of light and could provide new ways to control spin and valley degrees of freedom in a scalable photonic platform. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement}, issn = {1094-4087}, doi = {10.1364/OE.27.021367}, author = {Yang, Zhili and Aghaeimeibodi, Shahriar and Waks, Edo} } @article {ISI:000475514100001, title = {Cold hybrid ion-atom systems}, journal = {Rev. Mod. Phys.}, volume = {91}, number = {3}, year = {2019}, month = {JUL 15}, pages = {035001}, publisher = {AMER PHYSICAL SOC}, type = {Review}, abstract = {Hybrid systems of laser-cooled trapped ions and ultracold atoms combined in a single experimental setup have recently emerged as a new platform for fundamental research in quantum physics. This paper reviews the theoretical and experimental progress in research on cold hybrid ion-atom systems which aim to combine the best features of the two well-established fields. A broad overview is provided of the theoretical description of ion-atom mixtures and their applications, and a report is given on advances in experiments with ions trapped in Paul or dipole traps overlapped with a cloud of cold atoms, and with ions directly produced in a Bose-Einstein condensate. This review begins with microscopic models describing the electronic structure, interactions, and collisional physics of ion-atom systems at low and ultralow temperatures, including radiative and nonradiative charge-transfer processes and their control with magnetically tunable Feshbach resonances. Then the relevant experimental techniques and the intrinsic properties of hybrid systems are described. In particular, the impact is discussed of the micromotion of ions in Paul traps on ion-atom hybrid systems. Next, a review of recent proposals is given for using ions immersed in ultracold gases for studying cold collisions, chemistry, many-body physics, quantum simulation, and quantum computation and their experimental realizations. The last part focuses on the formation of molecular ions via spontaneous radiative association, photoassociation, magnetoassociation, and sympathetic cooling. Applications and prospects are discussed of cold molecular ions for cold controlled chemistry and precision spectroscopy.}, issn = {0034-6861}, doi = {10.1103/RevModPhys.91.035001}, author = {Tomza, Michal and Jachymski, Krzysztof and Gerritsma, Rene and Negretti, Antonio and Calarco, Tommaso and Idziaszek, Zbigniew and Julienne, Paul S.} } @article {ISI:000456032500004, title = {Conditions allowing error correction in driven qubits}, journal = {Phys. Rev. B}, volume = {99}, number = {4}, year = {2019}, month = {JAN 17}, pages = {045422}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We consider a qubit that is driven along its logical z axis, with noise along the z axis in the driving field Omega proportional to some function f (Omega), as well as noise along the logical x axis. We establish that whether or not errors due to both types of noise can be canceled out, even approximately, depends on the explicit functional form of f (Omega) by considering a power-law form, f (Omega) proportional to Omega(k). In particular, we show that such cancellation is impossible for k = 0, 1, or any even integer. However, any other odd integer value of k besides 1 does permit cancellation; in fact, we show that both types of errors can be corrected with a sequence of four square pulses of equal duration. We provide sets of parameters that correct for errors for various rotations and evaluate the error, measured by the infidelity, for the corrected rotations versus the naive rotations, i.e., the operations that, in the complete absence of noise, would produce the desired rotations (in this case a single pulse of appropriate duration and magnitude). We also consider a train of four trapezoidal pulses, which take into account the fact that there will be, in real experimental systems, a finite rise time, again providing parameters for error-corrected rotations that employ such pulse sequences. Our dynamical decoupling error correction scheme works for any qubit platform as long as the errors are quasistatic.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.045422}, author = {Throckmorton, Robert E. and S. Das Sarma} } @article {ISI:000456301900009, title = {Conductance smearing and anisotropic suppression of induced superconductivity in a Majorana nanowire}, journal = {Phys. Rev. B}, volume = {99}, number = {2}, year = {2019}, month = {JAN 22}, pages = {024510}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {In a recent high-quality experimental work on normal metal-superconducting nanowire junctions (J. D. S. Bommer et al., arXiv :1807.01940), strong anisotropic suppression of induced superconductivity has been observed in tunnel conductance measurements in the presence of applied magnetic field with variable orientation. Following this finding, we investigate theoretically the dependence of tunnel conductance on the direction of the Zeeman field in order to understand the operational mechanisms and to extract effective system parameters. Second, motivated by a generic discrepancy between experiment and theory, i.e., many in-gap and above-gap conductance features predicted by theory are barely observed in experiments, we study several mechanisms possibly responsible for the suppression of the theoretically predicted conductance features (e.g., length of the nanowire, self-energy effect due to the proximity effect, finite temperature, finite dissipation, and multiband effect). One essential finding in the current work is that only by a combined understanding of both suppression mechanisms can we extract effective system parameters from the experimental data (e.g., the effective nanowire-superconductor coupling, the effective Lande g factor, and the chemical potential of the semiconducting nanowire). In addition, we consider topologically trivial Andreev bound states in hybrid nanowires in the presence of potential inhomogeneities, such as external quantum dots or potential inhomogeneities inside the nanowire. We compare the anisotropic, field-dependent features induced by these nontopological Andreev bound states with the corresponding features produced by topological Majorana zero modes in pristine nanostructures, so that we can provide guidance to differentiate between the topologically trivial and nontrivial cases.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.024510}, author = {Liu, Chun-Xiao and Sau, Jay D. and Stanescu, Tudor D. and S. Das Sarma} } @article {ISI:000464756500001, title = {Confined Quasiparticle Dynamics in Long-Range Interacting Quantum Spin Chains}, journal = {Phys. Rev. Lett.}, volume = {122}, number = {15}, year = {2019}, month = {APR 16}, pages = {150601}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study the quasiparticle excitation and quench dynamics of the one-dimensional transverse-field Ising model with power-law (1/r(alpha)) interactions. We find that long-range interactions give rise to a confining potential, which couples pairs of domain walls (kinks) into bound quasiparticles, analogous to mesonic states in high-energy physics. We show that these quasiparticles have signatures in the dynamics of order parameters following a global quench, and the Fourier spectrum of these order parameters can be exploited as a direct probe of the masses of the confined quasiparticles. We introduce a two-kink model to qualitatively explain the phenomenon of long-range-interaction-induced confinement and to quantitatively predict the masses of the bound quasiparticles. Furthermore, we illustrate that these quasiparticle states can lead to slow thermalization of one-point observables for certain initial states. Our work is readily applicable to current trapped-ion experiments.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.122.150601}, author = {Liu, Fangli and Lundgren, Rex and Titum, Paraj and Pagano, Guido and Zhang, Jiehang and Monroe, Christopher and Gorshkov, V, Alexey} } @article { ISI:000504862300005, title = {Coupled electron-impurity and electron-phonon systems as trivial non-Fermi liquids}, journal = {Phys. Rev. B}, volume = {100}, number = {23}, year = {2019}, month = {DEC 30}, pages = {235149}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We consider an electron gas, both in two (2D) and three (3D) dimensions, interacting with quenched impurities and phonons within leading order finite-temperature many-body perturbation theories, calculating the electron self-energies, spectral functions, and momentum distribution functions at finite temperatures. The resultant spectral function is in general highly non-Lorentzian, indicating that the system is not a Fermi liquid in the usual sense. The calculated momentum distribution function cannot be approximated by a Fermi function at any temperature, providing a rather simple example of a non-Fermi liquid with well-understood properties.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.100.235149}, author = {Buterakos, Donovan and Das Sarma, Sankar} } @article {ISI:000478991700001, title = {Critical viscosity of a fluctuating superconductor}, journal = {Phys. Rev. B}, volume = {100}, number = {6}, year = {2019}, month = {AUG 2}, pages = {060501}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We consider a fluctuating superconductor in the vicinity of the transition temperature, T-c. The fluctuation shear viscosity is calculated. In two dimensions, the leading correction to viscosity is negative and scales as delta eta(T) alpha ln(T - T-c). Critical hydrodynamics of the fluctuating superconductor involves two fluids: a fluid of fluctuating pairs and a quasiparticle fluid of single-electron excitations. The pair viscosity (Aslamazov-Larkin) term is shown to be zero. The (density of states) correction to viscosity of single-electron excitations is negative, which is due to fluctuating pairing that results in a reduction of electron density. Scattering of electrons off of the fluctuations gives rise to an enhanced quasiparticle scattering and another (Maki-Thomson) negative correction to viscosity. Our results suggest that fluctuating superconductors provide a promising platform to investigate low-viscosity electronic media and may potentially host fermionic/electronic turbulence. Some experimental probes of two-fluid critical hydrodynamics are proposed such as time-of-flight measurement of turbulent energy cascades in critical cold atom superfluids and magnetic dynamos in three-dimensional fluctuating superconductors.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.100.060501}, author = {Liao, Yunxiang and Galitski, Victor} } @article { ISI:000447062400001, title = {Cryogenic trapped-ion system for large scale quantum simulation}, journal = {QUANTUM SCIENCE AND TECHNOLOGY}, volume = {4}, number = {1}, year = {2019}, month = {JAN}, pages = {UNSP 014004}, issn = {2058-9565}, doi = {10.1088/2058-9565/aae0fe}, author = {Pagano, G. and Hess, P. W. and Kaplan, H. B. and Tan, W. L. and Richerme, P. and Becker, P. and Kyprianidis, A. and Zhang, J. and Birckelbaw, E. and Hernandez, M. R. and Wu, Y. and Monroe, C.} } @article {ISI:000458854900004, title = {Curvature of gap closing features and the extraction of Majorana nanowire parameters}, journal = {Phys. Rev. B}, volume = {99}, number = {5}, year = {2019}, month = {FEB 15}, pages = {054507}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Recent tunneling conductance measurements of Majorana nanowires show a strong variation in the magnetic-field dependence of the superconducting gap among different devices. Here, we theoretically study the magnetic field dependence of the gap closing feature and establish that the degree of convexity (or concavity) of the gap closing as a function of Zeeman field can provide critical constraints on the underlying microscopic parameters of the semiconductor-superconductor hybrid system model. Specifically, we show that the gap closing feature is entirely concave only for strong spin-orbit coupling strength relative to the chemical potential. Additionally, the nonlinearity (i.e., concavity or convexity) of the gap closing as a function of magnetic field complicates the simple assignment of a constant effective g-factor to the states in the Majorana nanowire. We develop a procedure to estimate the effective g-factor from recent experimental data that accounts for the nonlinear gap closing, resulting from the interplay between chemical potential and spin-orbit coupling. Thus, measurements of the magnetic field dependence of the gap closure on the trivial side of the topological quantum phase transition can provide useful information on parameters that are critical to the theoretical modeling of Majorana nanowires.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.054507}, author = {Pan, Haining and Sau, Jay D. and Stanescu, Tudor D. and S. Das Sarma} } @article { ISI:000491132700014, title = {Demonstration of slow light in rubidium vapor using single photons from a trapped ion}, journal = {Sci. Adv.}, volume = {5}, number = {10}, year = {2019}, month = {OCT}, pages = {eaav4651}, publisher = {AMER ASSOC ADVANCEMENT SCIENCE}, type = {Article}, abstract = {Practical implementation of quantum networks is likely to interface different types of quantum systems. Photonically linked hybrid systems, combining unique properties of each constituent system, have typically required sources with the same photon emission wavelength. Trapped ions and neutral atoms both have compelling properties as nodes and memories in a quantum network but have never been photonically linked because of vastly different operating wavelengths. Here, we demonstrate the first interaction between neutral atoms and photons emitted from a single trapped ion. We use slow light in Rb-87 vapor to delay photons originating from a trapped Ba-138(+) ion by up to 13.5 +/- 0.5 ns, using quantum frequency conversion to overcome the frequency difference between the ion and neutral atoms. The delay is tunable and preserves the temporal profile of the photons. This result showcases a hybrid photonic interface usable as a synchronization tool-a critical component in any future large-scale quantum network.}, issn = {2375-2548}, doi = {10.1126/sciadv.aav4651}, author = {Siverns, J. D. and Hannegan, J. and Quraishi, Q.} } @conference {ISI:000484886200007, title = {Design and performance study of actively holding-off GHz-gated InGaAs/InP SPADs}, booktitle = {ADVANCED PHOTON COUNTING TECHNIQUES XIII}, series = {Proceedings of SPIE}, volume = {10978}, year = {2019}, note = {Conference on Advanced Photon Counting Techniques XIII, Baltimore, MD, APR 17-18, 2019}, pages = {109780C}, publisher = {SPIE}, organization = {SPIE}, type = {Proceedings Paper}, abstract = {High-speed periodic gating of InGaAs/InP single-photon avalanche diodes (SPADs) has allowed these detectors to operate at count rates above 108 per second with low afterpulsing. However, a drawback of high-speed periodic gating is that bias gates are applied continuously, regardless of whether an avalanche has occurred or not. This is disadvantageous because gates immediately following an avalanche have elevated afterpulse probabilities, and the additional charge from these secondary events contributes to the overall afterpulse probability. We investigate this phenomenon in a proof-of-principle experiment in which the series of bias gates is briefly interrupted after an avalanche, and we measure the resulting impact on the afterpulse probability. We observe a significant reduction in afterpulsing when such a bias-gate hold-off is applied to an InGaAs/InP SPAD gated at 1.25 GHz; when one bias gate is omitted after an avalanche the per-gate afterpulse probability is reduced by more than 40 \%. These results indicate that afterpulsing noise at high count rates can be further reduced in high-speed-gated SPADs.}, keywords = {afterpulsing, photon detection, quantum communication, single-photon avalanche diode, Single-photon detector}, isbn = {978-1-5106-2622-5}, issn = {0277-786X}, doi = {10.1117/12.2520620}, author = {Restelli, Alessandro and Bienfang, Joshua C. and Migdall, Alan L.}, editor = {Itzler, MA and Bienfang, JC and McIntosh, KA} } @article {ISI:000461830900002, title = {Development of transmon qubits solely from optical lithography on 300 mm wafers}, journal = {Quantum Sci. Technol.}, volume = {4}, number = {2}, year = {2019}, month = {APR}, pages = {025012}, publisher = {IOP PUBLISHING LTD}, type = {Article}, abstract = {Qubit information processors are increasing in footprint but currently rely on e-beam lithography for patterning the required Josephson junctions (JJs). Advanced optical lithography is an alternative patterning method, and we report on the development of transmon qubits patterned solely with optical lithography. The lithography uses 193 nm wavelength exposure and 300 mm large silicon wafers. Qubits and arrays of evaluation JJs were patterned with process control which resulted in narrow feature distributions: a standard deviation of 0.78\% for a 220 nm linewidth pattern realized across over half the width of the wafers. Room temperature evaluation found a 2.8\%-3.6\% standard deviation in JJ resistance in completed chips. The qubits used aluminum and titanium nitride films on silicon substrates without substantial silicon etching. T-1 times of the qubits were extracted at 26-27 mu s, indicating a low level of material-based qubit defects. This study shows that large wafer optical lithography on silicon is adequate for high-quality transmon qubits, and shows a promising path for improving many-qubit processors.}, keywords = {fabrication, large wafer, QUBIT, silicon, superconducting}, issn = {2058-9565}, doi = {10.1088/2058-9565/ab0ca8}, author = {Foroozani, N. and Hobbs, C. and Hung, C. C. and Olson, S. and Ashworth, D. and Holland, E. and Malloy, M. and Kearney, P. and O{\textquoteright}Brien, B. and Bunday, B. and DiPaola, D. and Advocate, W. and Murray, T. and Hansen, P. and Novak, S. and Bennett, S. and Rodgers, M. and Baker-O{\textquoteright}Neal, B. and Sapp, B. and Barth, E. and Hedrick, J. and Goldblatt, R. and Rao, S. S. Papa and Osborn, K. D.} } @article {ISI:000475496800004, title = {Diabatic errors in Majorana braiding with bosonic bath}, journal = {Phys. Rev. B}, volume = {100}, number = {1}, year = {2019}, month = {JUL 12}, pages = {014511}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Majorana mode based topological qubits are potentially subject to diabatic errors that in principle can limit the utility of topological quantum computation. Using a combination of analytical and numerical methods we study the diabatic errors in Majorana-based topological Y junction that are coupled to a Bosonic bath in the Markovian approximation. We find that in the absence of a bath, the error can be made exponentially small with increasing braiding time, only when the time variation in the Hamiltonian is completely smooth. The presence of a dominantly dissipative Markovian bath is found to eliminate this exponential scaling of error to a power-law scaling as T-1 with T being the braiding time. However, the inclusion of relaxation improves this scaling slightly to go as T-2. Thus, coupling of topological systems to Bosonic baths can lead to power law in braiding time diabatic errors that might limit the speed of topologically protected operations using Majorana modes.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.100.014511}, author = {Nag, Amit and Sau, Jay D.} } @article {ISI:000455814100005, title = {Dynamic polarizability measurements with Lu-176(+)}, journal = {Phys. Rev. A}, volume = {99}, number = {1}, year = {2019}, month = {JAN 15}, pages = {012510}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We measure the differential polarizability of the Lu-176(+) S-1(0) <-> D-3(1) clock transition at multiple wavelengths. This experimentally characterizes the differential dynamic polarizability for frequencies up to 372 THz and allows an experimental determination of the dynamic correction to the blackbody radiation shift for the clock transition. In addition, measurements at the near resonant wavelengths of 598 and 646 nm determine the two dominant contributions to the differential dynamic polarizability below 372 THz. These additional measurements are carried out by two independent methods to verify the validity of our methodology. We also carry out a theoretical calculation of the polarizabilities using the hybrid method that combines the configuration interaction (CI) and the coupled-cluster approaches, incorporating for the first time quadratic nonlinear terms and partial triple excitations in the coupled-cluster calculations. The experimental measurements of the vertical bar < D-3(1)parallel to r parallel to P-3(J)>vertical bar matrix elements provide high-precision benchmarks for this theoretical approach.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.99.012510}, author = {Arnold, K. J. and Kaewuam, R. and Tan, T. R. and Porsev, S. G. and Safronova, M. S. and Barrett, M. D.} } @article {ISI:000482136700013, title = {Dynamic suppression of Rayleigh backscattering in dielectric resonators}, journal = {Optica}, volume = {6}, number = {8}, year = {2019}, month = {AUG 20}, pages = {1016-1022}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {The ultimate limits of performance for any classical optical system are set by sub-wavelength fluctuations within the host material, which may be frozen-in or even dynamically induced. The most common manifestation of such subwavelength disorder is Rayleigh light scattering, which is observed in nearly all waveguiding technologies today and can lead to both irreversible radiative losses as well as undesirable intermodal coupling, While it has been shown that backscattering from disorder can be suppressed by breaking the time-reversal symmetry in magneto-optic and topological insulator materials, common optical dielectrics possess neither of these properties. Here, we demonstrate an optomechanical approach for dynamically suppressing Rayleigh backscattering within dielectric resonators. We achieve this by locally breaking the time-reversal symmetry in a silica resonator through a Brillouin scattering interaction that is available in all materials. Near-complete suppression of Rayleigh backscattering is experimentally confirmed through two independent measurements-the elimination of a commonly seen normal-mode splitting or {\textquoteleft}{\textquoteleft}doublet{{\textquoteright}{\textquoteright}} effect and by measurement of the reduction in intrinsic optical loss. Additionally, a reduction of the back-reflections caused by disorder is also observed. Our results provide new evidence that it is possible to dynamically suppress Rayleigh backscattering within any optical dielectric medium using time-reversal symmetry breaking, for achieving robust light propagation in spite of scatterers or defects. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement}, issn = {2334-2536}, doi = {10.1364/OPTICA.6.001016}, author = {Kim, Seunghwi and Taylor, Jacob M. and Bahl, Gaurav} } @article {ISI:000466037000001, title = {Dynamical Hamiltonian engineering of 2D rectangular lattices in a one-dimensional ion chain}, journal = {npj Quantum Inform.}, volume = {5}, year = {2019}, month = {APR 26}, pages = {32}, publisher = {SPRINGERNATURE}, type = {Article}, abstract = {Controlling the interaction graph between spins or qubits in a quantum simulator allows user-controlled tailoring of native interactions to achieve a target Hamiltonian. Engineering long-ranged phonon-mediated spin-spin interactions in a trapped ion quantum simulator offers such a possibility. Trapped ions, a leading candidate for quantum simulation, are most readily trapped in a linear 1D chain, limiting their utility for readily simulating higher dimensional spin models. In this work, we introduce a hybrid method of analog-digital simulation for simulating 2D spin models which allows for the dynamic changing of interactions to achieve a new graph using a linear 1D chain. We focus this numerical work on engineering 2D rectangular nearest-neighbor spin lattices, demonstrating that the required control parameters scale linearly with ion number. This hybrid approach offers compelling possibilities for the use of 1D chains in the study of Hamiltonian quenches, dynamical phase transitions, and quantum transport in 2D and 3D.}, doi = {10.1038/s41534-019-0147-x}, author = {Rajabi, Fereshteh and Motlakunta, Sainath and Shih, Chung-You and Kotibhaskar, Nikhil and Quraishi, Qudsia and Ajoy, Ashok and Islam, Rajibul} } @article { ISI:000505563100013, title = {Dynamics of analog logic-gate networks for machine learning}, journal = {Chaos}, volume = {29}, number = {12}, year = {2019}, month = {DEC}, pages = {123130}, publisher = {AMER INST PHYSICS}, type = {Article}, abstract = {We describe the continuous-time dynamics of networks implemented on Field Programable Gate Arrays (FPGAs). The networks can perform Boolean operations when the FPGA is in the clocked (digital) mode; however, we run the programed FPGA in the unclocked (analog) mode. Our motivation is to use these FPGA networks as ultrafast machine-learning processors, using the technique of reservoir computing. We study both the undriven dynamics and the input response of these networks as we vary network design parameters, and we relate the dynamics to accuracy on two machine-learning tasks. Published under license by AIP Publishing.}, issn = {1054-1500}, doi = {10.1063/1.5123753}, author = {Shani, Itamar and Shaughnessy, Liam and Rzasa, John and Restelli, Alessandro and Hunt, Brian R. and Komkov, Heidi and Lathrop, Daniel P.} } @article {ISI:000483304200006, title = {Efficient telecom-to-visible spectral translation through ultralow power nonlinear nanophotonics}, journal = {Nat. Photonics}, volume = {13}, number = {9}, year = {2019}, month = {SEP}, pages = {593+}, publisher = {NATURE PUBLISHING GROUP}, type = {Article}, abstract = {The ability to spectrally translate lightwave signals in a compact, low-power platform is at the heart of the promise of nonlinear nanophotonic technologies. For example, a device to connect the telecommunications band with visible and short near-infrared wavelengths can enable a connection between high-performance chip-integrated lasers based on scalable nanofabrication technology with atomic systems used for time and frequency metrology. Although second-order nonlinear (chi((2))) systems are the natural approach for bridging such large spectral gaps, here we show that third-order nonlinear (chi((3))) systems, despite their typically much weaker nonlinear response, can realize spectral translation with unprecedented performance. By combining resonant enhancement with nanophotonic mode engineering in a silicon nitride microring resonator, we demonstrate efficient spectral translation of a continuous-wave signal from the telecom band (similar to 1,550 nm) to the visible band (similar to 650 nm) through cavity-enhanced four-wave mixing. We achieve such translation over a wide spectral range >250 THz with a translation efficiency of (30.1 +/- 2.8)\% and using an ultralow pump power of (329 +/- 13) mu W. The translation efficiency projects to (274 +/- 28)\% at 1 mW and is more than an order of magnitude larger than what has been achieved in current nanophotonic devices.}, issn = {1749-4885}, doi = {10.1038/s41566-019-0464-9}, author = {Lu, Xiyuan and Moille, Gregory and Li, Qing and Westlyl, Daron A. and Singh, Anshuman and Rao, Ashutosh and Yu, Su-Peng and Briles, Travis C. and Papp, Scott B. and Srinivasan, Kartik} } @article {ISI:000466237600004, title = {Elastic rate coefficients for Li+H-2 collisions in the calibration of a cold-atom vacuum standard}, journal = {Phys. Rev. A}, volume = {99}, number = {4}, year = {2019}, month = {APR 29}, pages = {042704}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Ongoing efforts at the National Institute of Standards and Technology in creating a cold-atom vacuum standard device have prompted theoretical investigations of atom-molecule collision processes that characterize its operation. Such a device will operate as a primary standard for the ultrahigh-vacuum and extreme-high-vacuum regimes. This device operates by relating loss of ultracold lithium atoms from a conservative trap by collisions with ambient atoms and molecules to the background density and thus pressure through the ideal gas law. The predominant background constituent in these environments is molecular hydrogen H-2. We compute the relevant Li+H-2 Born-Oppenheimer potential energy surface, paying special attention to its uncertainty. Coupled-channel calculations are then used to obtain total rate coefficients, which include momentum-changing elastic and inelastic processes. We find that inelastic rotational quenching of H-2 is negligible near room temperature. For a (T = 300)-K gas of H-2 and 1.0-mu K gas of Li atoms prepared in a single hyperfine state, the total rate coefficients are 6.0(1) x 10(-9) cm(3)/s for both Li-6 and Li-7 isotopes, where the number in parentheses corresponds to a one-standard-deviation combined statistical and systematic uncertainty. We find that a 10-K increase in the H-2 temperature leads to a 1.9\% increase in the rate coefficients for both isotopes. For Li temperatures up to 100 mu K, changes are negligible. Finally, a semiclassical Born approximation significantly overestimates the rate coefficients. The difference is at least ten times the uncertainty of the coupled-channel result.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.99.042704}, author = {Makrides, Constantinos and Barker, Daniel S. and Fedchak, James A. and Scherschligt, Julia and Eckel, Stephen and Tiesinga, Eite} } @article {ISI:000460648100005, title = {Electric dipole matrix elements for the 6p(2)P(J) -> 7s(2)S(1/2) transition in atomic cesium}, journal = {Phys. Rev. A}, volume = {99}, number = {3}, year = {2019}, month = {MAR 5}, pages = {032504}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We report a measurement of the ratio of electric dipole transition matrix elements of cesium for the 6p(2)P(1/2) -> 7s(2)S(1/2) and 6p(2)P(3/2) -> 7s(2)S(1/2 )transitions. We determine this ratio of matrix elements through comparisons of two-color, two-photon excitation rates of the 7s(2)S(1/2) state using laser beams with polarizations parallel to one another vs perpendicular to one another. Our result of R < 7s(2)S(1/2)parallel to r parallel to 6P(2)P(3/2)>/< 7s(2)S(1/2)parallel to r parallel to 6P(2)P(1/2)> = 1.5272(17) is in excellent agreement with a theoretical prediction of R = 1.5270(27). Moreover, the accuracy of the experimental ratio is sufficiently high to differentiate between various theoretical approaches. To our knowledge, there are no prior experimental measurements of R. Combined with our recent determination of the lifetime of the 7s(2)S(1/2) state, we determine reduced matrix elements for these two transitions, < 7s(2)S(1/2)parallel to r parallel to 6P(2)P(3/2)> = -6.489(5)a(0) and < 7s(2)S(1/2)parallel to r parallel to 6P(2)P(1/2 >) = -4.249(4)a(0). These matrix elements are also in excellent agreement with theoretical calculations. These measurements improve knowledge of Cs properties needed for parity violation studies and provide benchmarks for tests of high-precision theory.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.99.032504}, author = {Toh, George and Damitz, Amy and Glotzbach, Nathan and Quirk, Jonah and Stevenson, I. C. and Choi, J. and Safronova, M. S. and Elliott, D. S.} } @article {ISI:000468201600010, title = {Electromagnetically induced transparency in inhomogeneously broadened solid media}, journal = {Phys. Rev. A}, volume = {99}, number = {5}, year = {2019}, month = {MAY 15}, pages = {053821}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study, theoretically and experimentally, electromagnetically induced transparency (EIT) in two different solid-state systems. Unlike many implementations in homogeneously broadened media, these systems exhibit inhomogeneous broadening of their optical and spin transitions typical of solid-state materials. We observe EIT line shapes typical of atomic gases, including a crossover into the regime of Autler-Townes splitting, but with the substitution of the inhomogeneous widths for the homogeneous values. We obtain quantitative agreement between experiment and theory for the width of the transparency feature over a range of optical powers and inhomogeneous linewidths. We discuss regimes over which analytical and numerical treatments capture the behavior. As solid-state systems become increasingly important for scalable and integratable quantum optical and photonic devices, it is vital to understand the effects of the inhomogeneous broadening that is ubiquitous in these systems. The treatment presented here can be applied to a variety of systems, as exemplified by the common scaling of experimental results from two different systems.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.99.053821}, author = {Fan, H. Q. and Kagalwala, K. H. and Polyakov, V, S. and Migdall, A. L. and Goldschmidt, E. A.} } @article {ISI:000466405300001, title = {Electronic structure of full-shell InAs/Al hybrid semiconductor-superconductor nanowires: Spin-orbit coupling and topological phase space}, journal = {Phys. Rev. B}, volume = {99}, number = {16}, year = {2019}, month = {APR 26}, pages = {161118}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study the electronic structure of full-shell superconductor-semiconductor nanowires, which have recently been proposed for creating Majorana zero modes, using an eight-band (k) over right arrow . (p) over right arrow model within a fully self-consistent Schrodinger-Poisson scheme. We find that the spin-orbit coupling induced by the intrinsic radial electric field is generically weak for subbands with their minimum near the Fermi energy. Furthermore, we show that the chemical potential windows consistent with the emergence of a topological phase are small and sparse and can only be reached by fine-tuning the diameter of the wire. These findings suggest that the parameter space consistent with the realization of a topological phase in full-shell InAs/Al nanowires is, at best, very narrow.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.161118}, author = {Woods, Benjamin D. and S. Das Sarma and Stanescu, Tudor D.} } @article {ISI:000468026100013, title = {Emergent gauge field and the Lifshitz transition of spin-orbit coupled bosons in one dimension}, journal = {Sci Rep}, volume = {9}, year = {2019}, month = {MAY 16}, pages = {7471}, publisher = {NATURE PUBLISHING GROUP}, type = {Article}, abstract = {In the presence of strong spin-independent interactions and spin-orbit coupling, we show that the spinor Bose liquid confined to one spatial dimension undergoes an interaction-or density-tuned quantum phase transition similar to one theoretically proposed for itinerant magnetic solid-state systems. The order parameter describes broken Z2 inversion symmetry, with the ordered phase accompanied by non-vanishing momentum which is generated by fluctuations of an emergent dynamical gauge field at the phase transition. This quantum phase transition has dynamical critical exponent z similar or equal to 2, typical of a Lifshitz transition, but is described by a nontrivial interacting fixed point. From direct numerical simulation of the microscopic model, we extract previously unknown critical exponents for this fixed point. Our model describes a realistic situation of 1D ultracold atoms with Raman-induced spin-orbit coupling, establishing this system as a platform for studying exotic critical behavior of the Hertz-Millis type.}, issn = {2045-2322}, doi = {10.1038/s41598-019-43929-6}, author = {Cole, William S. and Lee, Junhyun and Mahmud, Khan W. and Alavirad, Yahya and Spielman, I. B. and Sau, Jay D.} } @article {ISI:000466716100027, title = {The end of artefacts}, journal = {Nat. Phys.}, volume = {15}, number = {5}, year = {2019}, month = {MAY}, pages = {518}, publisher = {NATURE PUBLISHING GROUP}, type = {Editorial Material}, issn = {1745-2473}, doi = {10.1038/s41567-019-0514-8}, author = {Phillips, William D.} } @article {ISI:000471983700002, title = {Equilibration of quasi-one-dimensional Fermi gases}, journal = {Phys. Rev. B}, volume = {99}, number = {24}, year = {2019}, month = {JUN 11}, pages = {245121}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {One-dimensional systems often possess multiple channels or bands arising from the excitation of transverse degrees of freedom. In this work, we study the specific processes that dominate the equilibration of multichannel Fermi gases at low temperatures. Focusing on the case of two channels, we perform an analysis of the relaxation properties of these systems by studying the spectrum and eigenmodes of the linearized collision integral. As an application of this analysis, a detailed calculation of the bulk viscosity is presented. The dominant scattering processes obey an unexpected conservation law which is likely to affect the hydrodynamic behavior of these systems.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.245121}, author = {DeGottardi, Wade and Matveev, K. A.} } @article {ISI:000476581500009, title = {Evanescent modes and step-like acoustic black holes}, journal = {Ann. Phys.}, volume = {407}, year = {2019}, month = {AUG}, pages = {148-165}, publisher = {ACADEMIC PRESS INC ELSEVIER SCIENCE}, type = {Article}, abstract = {We consider a model of an acoustic black hole formed by a quasi-one dimensional Bose-Einstein condensate with a step-like horizon. This system is analyzed by solving the corresponding Bogoliubov-de Gennes equation with an appropriate matching condition at the jump. When the step is between a subsonic and supersonic flow, a sonic horizon develops and in addition to the scattering coefficients we compute the distribution of the accompanying analogue Hawking radiation. Additionally, in response to the abrupt variation in flow and non-linear Bogoliubov dispersion relation, evanescent solutions of the Bogoliubov-de Gennes equation also appear and decay out from the horizon. We bound this decay length and show that these modes produce a modulation of observables outside the event horizon by their interference with outgoing Hawking flux. We go further and find specific superpositions of ingoing eigenmodes which exhibit coherent cancellation of the Hawking flux outside the horizon but nevertheless have evanescent support outside the black hole. We conclude by speculating that when quasiparticle interactions are included, evanescent modes may yield a leakage of information across the event horizon via interactions between the real outgoing Hawking flux and the virtual evanescent modes, and that we may expect this as a generic feature of models which break Lorentz invariance at the UV (Planck) scale. (C) 2019 Elsevier Inc. All rights reserved.}, keywords = {Acoustic black hole, Analogue gravity, Bogoliubov-de Gennes quasiparticle, Bose-Einstein condensate, Evanescent mode, Hawking radiation}, issn = {0003-4916}, doi = {10.1016/j.aop.2019.04.017}, author = {Curtis, Jonathan and Refael, Gil and Galitski, Victor} } @article {ISI:000473271300044, title = {Evolution of large-scale flow from turbulence in a two-dimensional superfluid}, journal = {Science}, volume = {364}, number = {6447}, year = {2019}, month = {JUN 28}, pages = {1267+}, publisher = {AMER ASSOC ADVANCEMENT SCIENCE}, type = {Article}, abstract = {Nonequilibrium interacting systems can evolve to exhibit large-scale structure and order. In two-dimensional turbulent flow, the seemingly random swirling motion of a fluid can evolve toward persistent large-scale vortices. To explain such behavior, Lars Onsager proposed a statistical hydrodynamic model based on quantized vortices. Here, we report on the experimental confirmation of Onsager{\textquoteright}s model. We dragged a grid barrier through an oblate superfluid Bose-Einstein condensate to generate nonequilibrium distributions of vortices. We observed signatures of an inverse energy cascade driven by the evaporative heating of vortices, leading to steady-state configurations characterized by negative absolute temperatures. Our results open a pathway for quantitative studies of emergent structures in interacting quantum systems driven far from equilibrium.}, issn = {0036-8075}, doi = {10.1126/science.aat5793}, author = {Johnstone, Shaun P. and Groszek, Andrew J. and Starkey, Philip T. and Billington, Christopher J. and Simula, Tapio P. and Helmerson, Kristian} } @article {ISI:000476695900010, title = {Exact Localized and Ballistic Eigenstates in Disordered Chaotic Spin Ladders and the Fermi-Hubbard Model}, journal = {Phys. Rev. Lett.}, volume = {123}, number = {3}, year = {2019}, month = {JUL 16}, pages = {036403}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We demonstrate the existence of exact atypical many-body eigenstates in a class of disordered, interacting one-dimensional quantum systems that includes the Fermi-Hubbard model as a special case. These atypical eigenstates, which generically have finite energy density and are exponentially many in number, are populated by noninteracting excitations. They can exhibit Anderson localization with area-law eigenstate entanglement or, surprisingly, ballistic transport at any disorder strength. These properties differ strikingly from those of typical eigenstates nearby in energy, which we show give rise to diffusive transport as expected in a chaotic quantum system. We discuss how to observe these atypical eigenstates in cold-atom experiments realizing the Fermi-Hubbard model, and comment on the robustness of their properties.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.123.036403}, author = {Iadecola, Thomas and Znidaric, Marko} } @article {ISI:000463834800010, title = {Excitations and correlations in the driven-dissipative Bose-Hubbard model}, journal = {Phys. Rev. A}, volume = {99}, number = {4}, year = {2019}, month = {APR 4}, pages = {043607}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Using a field-theoretic approach within the Schwinger-Keldysh formalism, we study a Bose-Hubbard model in the presence of a driving field and dissipation due to one-body losses. We recover the bistability diagram from the Gross-Pitaevski equation, and analyze the different phases with respect to their elementary excitations and correlations. We find the low-density solution to be subdivided into a dynamically instable, a gapped, and a gapless regime. The correlations decay exponentially, but a substantial increase of correlation length marks the regime of gapless excitations.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.99.043607}, author = {Grass, Tobias} } @article { ISI:000504435500005, title = {Ferromagnetism in quantum dot plaquettes}, journal = {Phys. Rev. B}, volume = {100}, number = {22}, year = {2019}, month = {DEC 23}, pages = {224421}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Following recent experimental progress concerning Nagaoka ferromagnetism in finite-size quantum dot plaquettes, a general theoretical analysis is warranted in order to ascertain in rather generic terms which arrangements of a small number of quantum dots can produce saturated ferromagnetic ground states and under which constraints on interaction and interdot tunneling in the plaquette. This is particularly necessary since Nagaoka ferromagnetism is fragile and arises only under rather special conditions. We test the robustness of ground state ferromagnetism in the presence of a long-range Coulomb interaction and long-range as well as short-range interdot hopping by modeling a wide range of different plaquette geometries accessible by arranging a few (similar to 4) quantum dots in a controlled manner. We find that ferromagnetism is robust to the presence of long-range Coulomb interactions, and we develop conditions constraining the tunneling strength such that the ground state is ferromagnetic. Additionally, we predict the presence of a partially spin-polarized ferromagnetic state for 4 electrons in a Y-shaped 4-quantum-dot plaquette. Finally, we consider 4 electrons in a ring of 5 dots. This does not satisfy the Nagaoka condition; however, we show that the ground state is spin 1 for strong, but not infinite, on-site interaction. Thus, even though Nagaoka{\textquoteright}s theorem does not apply, the ground state for the finite system with one hole in a ring of 5 dots is partially ferromagnetic. We provide detailed fully analytical results for the existence or not of ferromagnetic ground states in several quantum dot geometries which can be studied in currently available coupled quantum dot systems.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.100.224421}, author = {Buterakos, Donovan and Das Sarma, Sankar} } @article {ISI:000466889100001, title = {A fiber-integrated nanobeam single photon source emitting at telecom wavelengths}, journal = {Appl. Phys. Lett.}, volume = {114}, number = {17}, year = {2019}, month = {APR 29}, pages = {171101}, publisher = {AMER INST PHYSICS}, type = {Article}, abstract = {Fiber-coupled single photon sources are considered important components of photonics-based quantum information processors. Most fibercoupled single photon sources require careful alignment between fibers and quantum emitters. In this work, we present an alignment-free fiber-integrated single photon source based on an InAs/InP quantum dot emitting at telecom wavelengths. We designed a nanobeam containing the quantum dots attached to a fiber taper. The adiabatic tapered coupler of the nanobeam enables efficient light coupling to the fiber taper. Using a tungsten probe in a focused ion beam system, we transferred the nanobeam to the fiber taper. The observed fiber-coupled single photon emission occurs with a brightness of 1.4\% and a purity of 83\%. This device provides a building block for fiber-optic quantum circuits that have various applications, such as quantum communication and distributed quantum computing. Published under license by AIP Publishing.}, issn = {0003-6951}, doi = {10.1063/1.5089907}, author = {Lee, Chang-Min and Buyukkaya, Mustafa Atabey and Aghaeimeibodi, Shahriar and Karasahin, Aziz and Richardson, Christopher J. K. and Waks, Edo} } @conference {ISI:000482226300153, title = {First experimental steps toward an in situ gauge for direct measurement of relativistic intensities}, booktitle = {2019 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO)}, series = {Conference on Lasers and Electro-Optics}, year = {2019}, note = {Conference on Lasers and Electro-Optics (CLEO), San Jose, CA, MAY 05-10, 2019}, publisher = {IEEE; AdValue Photon; Amer Elements; Class5 Photon; Coherent; GoFoton; Light Convers; LightTrans; MKS; OZ Opt Online; Santec; ThorLabs; UQDevices; YSL Photon}, organization = {IEEE; AdValue Photon; Amer Elements; Class5 Photon; Coherent; GoFoton; Light Convers; LightTrans; MKS; OZ Opt Online; Santec; ThorLabs; UQDevices; YSL Photon}, type = {Proceedings Paper}, abstract = {Nearly 50 years ago Sarachik and Schappert suggested an intensity gauge based on wavelength shifts due to relativistic Thomson scattering. We present the first preliminary experimental results exploiting these shifts to make a direct measurement of peak intensities above 10(18) W/cm(2). (C) 2019 The Author(s)}, isbn = {978-1-943580-57-6}, issn = {2160-9020}, author = {Hill, III, W. T. and He, C. and Roso, L. and Perez-Hernandez, J. A. and Gatti, G. and de Marco, M. and Fedosejevs, R. and Longman, A.} } @article {ISI:000477908400014, title = {Fluctuation-dissipation and correlation-propagation relations from the nonequilibrium dynamics of detector-quantum field systems}, journal = {Phys. Rev. D}, volume = {100}, number = {2}, year = {2019}, month = {JUL 29}, pages = {025019}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We consider N uniformly accelerating Unruh-DeWitt detectors whose internal degrees of freedom are coupled to a massless scalar field in (1 + 1)D Minkowski space. We use the influence functional formalism to derive the Langevin equations governing the nonequilibrium dynamics of the internal degrees of freedom and show explicitly that the system relaxes in time and equilibrates. We also show that once the equilibrium condition is established a set of fluctuation-dissipation relations (FDRs) and correlation-propagation relations emerges for the detectors, extending earlier results of Raval, Hu, and Anglin {[}Stochastic theory of accelerated detectors in quantum fields, Phys. Rev. D 53, 7003 (1996)] which discovered these relations for the quantum field. Although similar in form to the FDRs commonly known from linear response theory, which assumes an equilibrium condition a priori, their physical connotations are dissimilar from that of a nonequilibrium origin. We show explicitly that both sets of relations are needed to guarantee the balance of energy flow in and out of the system in dynamical equilibrium with the field. These results are helpful to investigations of quantum information and communications of detectors in space experiments and inquiries of theoretical issues in black holes and cosmology.}, issn = {2470-0010}, doi = {10.1103/PhysRevD.100.025019}, author = {Hsiang, Jen-Tsung and Hu, B. L. and Lin, Shih-Yuin} } @article {ISI:000477924000099, title = {Fluctuation-dissipation and correlation-propagation relations in (1+3)D moving detector-quantum field systems}, journal = {Phys. Lett. B}, volume = {795}, year = {2019}, month = {AUG 10}, pages = {694-699}, publisher = {ELSEVIER}, type = {Article}, abstract = {The fluctuation-dissipation relations (FDR) are powerful relations which can capture the essence of the interplay between a system and its environment. Challenging problems of this nature which FDRs aid in our understanding include the backreaction of quantum field processes like particle creation on the spacetime dynamics in early universe cosmology or quantum black holes. The less familiar, yet equally important correlation-propagation relations (CPR) relate the correlations of stochastic forces on different detectors to the retarded and advanced parts of the radiation propagated in the field. Here, we analyze a system of N uniformly-accelerated Unruh-DeWitt detectors whose internal degrees of freedom (idf) are minimally coupled to a real, massless, scalar field in 4D Minkowski space, extending prior work in 2D with derivative coupling. Using the influence functional formalism, we derive the stochastic equations describing the nonequilibrium dynamics of the idfs. We show after the detector-field dynamics has reached equilibration the existence of the FDR and the CPR for the detectors, which combine to form a generalized fluctuation-dissipation matrix relation. We show explicitly the energy flows between the constituents of the system of detectors and between the system and the quantum field environment. This power balance anchors the generalized FDR. We anticipate this matrix relation to provide a useful guardrail in expounding some basic issues in relativistic quantum information, such as ensuring the self-consistency of the energy balance and tracking the quantum information transfer in the detector-field system. (C) 2019 The Authors. Published by Elsevier B.V.}, issn = {0370-2693}, doi = {10.1016/j.physletb.2019.06.062}, author = {Hsiang, Jen-Tsung and Hu, B. L. and Lin, Shih-Yuin and Yamamoto, Kazuhiro} } @article {14546, title = {Fluctuation-Induced Torque on a Topological Insulator out of Thermal Equilibrium}, journal = {Phys. Rev. Lett.}, volume = {123}, year = {2019}, month = {Aug}, pages = {055901}, doi = {10.1103/PhysRevLett.123.055901}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.123.055901}, author = {Maghrebi, M. F. and Gorshkov, A. V. and Sau, J. D.} } @article {ISI:000457058500007, title = {Fractional Josephson effect with and without Majorana zero modes}, journal = {Phys. Rev. B}, volume = {99}, number = {3}, year = {2019}, month = {JAN 29}, pages = {035312}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {It is known that the low-energy physics of the Josephson effect in the presence of Majorana zero modes exhibits a 4 pi periodicity as the Aharonov-Bohm flux varies in contrast to the 2 pi Josephson periodicity in usual superconducting junctions. We study this fractional Josephson effect in one-dimensional topological superconductors in Majorana nanowire systems by focusing on the features of the phase-energy relations in a superconducting semiconductor nanowire with spin-orbital coupling by including different factors operational in experimental systems, such as short wire length, suppression of superconducting gap, and the presence of an Andreev bound state. We show that even in the absence of the Majorana zero modes, some nontopological physical effects can manifest a 4 pi periodicity of the phase-energy relation in the Josephson junction, thus providing an alternative physics for fractional Josephson effect with no underlying Majorana zero modes. Furthermore, we consider several scenarios of inhomogeneous chemical potential distributions in the superconducting nanowire leading to four Majorana bound states and construct the effective four-Majorana model to correctly describe the low-energy theory of the Josephson effect. In this setup, multiple Majorana zero modes can also have the 4 pi fractional Josephson effect, although the underlying physics arises from Andreev bound states since two close-by Majorana bound states effectively form Andreev bound states. Our work demonstrates that the mere observation of a fractional Josephson effect simulating 4 pi periodicity might not, by itself, be taken as the definitive evidence for topological superconductivity. This finding has important implications for the ongoing search for non-Abelian Majorana zero modes and efforts for developing topological qubits.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.035312}, author = {Chiu, Ching-Kai and S. Das Sarma} } @article {ISI:000482940400006, title = {Frequency shifts due to Stark effects on a rubidium two-photon transition}, journal = {Phys. Rev. A}, volume = {100}, number = {2}, year = {2019}, month = {AUG 28}, pages = {023417}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The 5S(1/2) -> 5D(5/2) two-photon transition in Rb is of interest for the development of a compact optical atomic clock. Here we present a rigorous calculation of the 778.1-nm ac Stark shift {[}2.30(4) x 10(-13)(mW/mm(2))(-1)] that is in good agreement with our measured value of 2.5(2) x 10(-13)(mW/mm(2))(-1). We include a calculation of the temperature-dependent blackbody radiation (BBR) shift, and we predict that the clock could be operated either with zero net BBR shift {[}T = 495.9(27) K] or with zero first-order sensitivity {[}T = 368.1(14) K]. Also described is the calculation of the dc Stark shift of 5.5(1) x 10(-15)/(V/cm(2)) as well as clock sensitivities to optical alignment variations in both a cat{\textquoteright}s eye and a flat mirror retroreflector. Finally, we characterize these Stark effects, discussing mitigation techniques necessary to reduce final clock instabilities.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.100.023417}, author = {Martin, Kyle W. and Stuhl, Benjamin and Eugenio, Jon and Safronova, Marianna S. and Phelps, Gretchen and Burke, John H. and Lemke, Nathan D.} } @article {ISI:000452005100052, title = {Gateless and reversible Carrier density tunability in epitaxial graphene devices functionalized with chromium tricarbonyl}, journal = {Carbon}, volume = {142}, year = {2019}, month = {FEB}, pages = {468-474}, publisher = {PERGAMON-ELSEVIER SCIENCE LTD}, type = {Article}, abstract = {Monolayer epitaxial graphene (EG) has been shown to have clearly superior properties for the development of quantized Hall resistance (QHR) standards. One major difficulty with QHR devices based on EG is that their electrical properties drift slowly over time if the device is stored in air due to adsorption of atmospheric molecular dopants. The crucial parameter for device stability is the charge carrier density, which helps determine the magnetic flux density required for precise QHR measurements. This work presents one solution to this problem of instability in air by functionalizing the surface of EG devices with chromium tricarbonyl - Cr(CO)(3). Observations of carrier density stability in air over the course of one year are reported, as well as the ability to tune the carrier density by annealing the devices. For low temperature annealing, the presence of Cr(CO)(3) stabilizes the electrical properties and allows for the reversible tuning of the carrier density in millimeter-scale graphene devices close to the Dirac point. Precision measurements in the quantum Hall regime show no detrimental effect on the carrier mobility. Published by Elsevier Ltd.}, issn = {0008-6223}, doi = {10.1016/j.carbon.2018.10.085}, author = {Rigosi, Albert F. and Kruskopf, Mattias and Hill, Heather M. and Jin, Hanbyul and Wu, Bi-Yi and Johnson, Philip E. and Zhang, Siyuan and Berilla, Michael and Walker, Angela R. Hight and Hacker, Christina A. and Newell, David B. and Elmquist, Randolph E.} } @article { ISI:000493516700001, title = {Gauging fractons: Immobile non-Abelian quasiparticles, fractals, and position-dependent degeneracies}, journal = {Phys. Rev. B}, volume = {100}, number = {15}, year = {2019}, month = {OCT 29}, pages = {155146}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The study of gapped quantum many-body systems in three spatial dimensions has uncovered the existence of quantum states hosting quasiparticles that are confined, not by energetics but by the structure of local operators, to move along lower dimensional submanifolds. These so-called {\textquoteleft}{\textquoteleft}fracton{{\textquoteright}{\textquoteright}} phases are beyond the usual topological quantum field theory description, and thus require new theoretical frameworks to describe them. Here we consider coupling fracton models to topological quantum field theories in (3 + 1) dimensions by starting with two copies of a known fracton model and gauging the Z(2) symmetry that exchanges the two copies. This yields a class of exactly solvable lattice models that we study in detail for the case of the X-cube model and Haah{\textquoteright}s cubic code. The resulting phases host finite-energy non-Abelian immobile quasiparticles with robust degeneracies that depend on their relative positions. The phases also host non-Abelian string excitations with robust degeneracies that depend on the string geometry. Applying the construction to Haah{\textquoteright}s cubic code in particular provides an exactly solvable model with finite energy yet immobile non-Abelian quasiparticles that can only be created at the corners of operators with fractal support.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.100.155146}, author = {Bulmash, Daniel and Barkeshli, Maissam} } @article {14901, title = {Generation and detection of spin-orbit coupled neutron beams}, journal = {Proceedings of the National Academy of Sciences}, volume = {116}, year = {2019}, pages = {20328{\textendash}20332}, abstract = {Extensive interest has been placed on the techniques to prepare and characterize optical and matter wave orbital angular momentum (OAM) beams and spin correlated OAM beams. They have been shown to be useful in a wide range of applications such as microscopy, quantum information processing, material characterization, and communication protocols. Here we demonstrate an observation of spin-orbit beams and lattices of spin-orbit beams with neutrons. Neutrons, which do not possess a charge and have significant mass, are probes of nature that are complementary to photons and electrons. The techniques shown here enable neutron OAM applications in material characterization and fundamental physics.Spin-orbit coupling of light has come to the fore in nanooptics and plasmonics, and is a key ingredient of topological photonics and chiral quantum optics. We demonstrate a basic tool for incorporating analogous effects into neutron optics: the generation and detection of neutron beams with coupled spin and orbital angular momentum. The 3He neutron spin filters are used in conjunction with specifically oriented triangular coils to prepare neutron beams with lattices of spin-orbit correlations, as demonstrated by their spin-dependent intensity profiles. These correlations can be tailored to particular applications, such as neutron studies of topological materials.

}, issn = {0027-8424}, doi = {10.1073/pnas.1906861116}, url = {https://www.pnas.org/content/116/41/20328}, author = {Sarenac, Dusan and Kapahi, Connor and Chen, Wangchun and Clark, Charles W. and Cory, David G. and Huber, Michael G. and Taminiau, Ivar and Zhernenkov, Kirill and Pushin, Dmitry A.} } @article {ISI:000468210200030, title = {Graphene Devices for Tabletop and High-Current Quantized Hall Resistance Standards}, journal = {IEEE Trans. Instrum. Meas.}, volume = {68}, number = {6, SI}, year = {2019}, month = {JUN}, pages = {1870-1878}, publisher = {IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC}, type = {Article}, abstract = {We report the performance of a quantum Hall resistance standard based on epitaxial graphene maintained in a 5-T tabletop cryocooler system. This quantum resistance standard requires no liquid helium and can operate continuously, allowing year-round accessibility to quantized Hall resistance measurements. The nu = 2 plateau, with a value of R-K/2, also seen as RH, is used to scale to 1 k Omega using a binary cryogenic current comparator (BCCC) bridge and a direct current comparator (DCC) bridge. The uncertainties achieved with the BCCC are such as those obtained in the state-of-the-art measurements using GaAs-based devices. BCCC scaling methods can achieve large resistance ratios of 100 or more, and while room temperature DCC bridges have smaller ratios and lower current sensitivity, they can still provide alternate resistance scaling paths without the need for cryogens and superconducting electronics. Estimates of the relative uncertainties of the possible scaling methods are provided in this report, along with a discussion of the advantages of several scaling paths. The tabletop system limits are addressed as are potential solutions for using graphene standards at higher currents.}, keywords = {Binary cryogenic current comparator (BCCC), direct current comparator (DCC), Epitaxial graphene (EG), Metrology, quantized Hall resistance (QHR), standard resistor, standards and calibration}, issn = {0018-9456}, doi = {10.1109/TIM.2018.2882958}, author = {Rigosi, Albert F. and Panna, Alireza R. and Payagala, Shamith U. and Kruskopf, Mattias and Kraft, Marlin E. and Jones, George R. and Wu, Bi-Yi and Lee, Hsin-Yen and Yang, Yanfei and Hu, Jiuning and Jarrett, Dean G. and Newell, David B. and Elmquist, Randolph E.} } @article {ISI:000471944200018, title = {Griffiths physics in an ultracold Bose gas}, journal = {Phys. Rev. A}, volume = {99}, number = {6}, year = {2019}, month = {JUN 17}, pages = {063611}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Coupled XY model systems consisting of three-dimensional (3D) systems with disordered interlayer physics are of significant theoretical interest. We realize a set of coupled quasi-2D layers of Rb-87 in the presence of disordered interlayer coupling. This is achieved with our high bandwidth arbitrary optical lattice to obviate restrictions on the dimensionality of disorder with speckle-generated optical fields. We identify phase crossover regions compatible with the existence of a pair of intermediate Griffiths phases between a thermal state and the emergence of bulk 3D superfluidity.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.99.063611}, author = {Reed, M. E. W. and Smith, Z. S. and Dewan, Aftaab and Rolston, S. L.} } @article { ISI:000504638400005, title = {Ground state excitation of an atom strongly coupled to a free quantum field}, journal = {Phys. Rev. D}, volume = {100}, number = {12}, year = {2019}, month = {DEC 26}, pages = {125019}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {This paper presents a nonperturbative treatment of strong-coupling induced effects in atom-field systems which cannot be seen in traditional perturbative treatments invoking compromising assumptions such as the Born-Markov, rotating wave, or Fermi Golden rule. We consider an atom whose internal degrees of freedom are modeled by a harmonic oscillator which is bilinearly coupled to a scalar quantum field, representing one of the two polarizations of an electromagnetic field. Because the whole system is Gaussian we can solve this problem exactly. Using the open quantum system conceptual framework and the influence functional formalism we derive the dynamics of the reduced density matrix for the atom which enables the calculation of atomic transition probability and other relevant physical quantities. Finding an exact solution to this problem has the distinct advantage of enabling one to capture fully the strong coupling regime and discover interesting effects such as spontaneous ground state excitation {[}R. Passante, T. Petrosky, and I. Prigogine, Long-time behaviour of self-dressing and indirect spectroscopy, Physica (Amsterdam) 218A, 437 (1995).] which is unfathomable in perturbative treatments. The conventional description of atomic-optical activities is predicated on the assumption that the state of the total atom-field system is a product state of the atomic excitations and the photon number states, an assumption which is valid only for vanishingly weak coupling. The correct energy eigenfunctions to use should be that of the Hamiltonian of the combined atom-field system. Other features associated with finite to strong coupling effects such as resonance peak broadening and transition from a gapped to a gapless spectrum can all be understood from this perspective. Finally, to put the issues in a proper perspective we take the perturbative limit of the exact results and compare them with those from conventional time-dependent perturbation theory (TDPT). This enables one to pin-point where the deficiencies of TDPT lie as one removes the ultraweak coupling assumption.}, issn = {2470-0010}, doi = {10.1103/PhysRevD.100.125019}, author = {Hsiang, Jen-Tsung and Hu, Bei-Lok} } @article {ISI:000483803100006, title = {Ground state of the three-dimensional BCS d-wave superconductor}, journal = {Phys. Rev. B}, volume = {100}, number = {10}, year = {2019}, month = {SEP 4}, pages = {104503}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We determine the mean-field ground state of the three-dimensional rotationally symmetric d-wave (l = 2) superconductor at weak coupling. It is a noninert state, invariant under the symmetry C-2 only, which breaks time-reversal symmetry almost maximally, and features a high but again less-than-maximal average magnetization. The state obtained by minimization of the expanded sixth-order Ginzburg-Landau free energy is found to be an excellent approximation to the true ground state. The coupling to a parasitic s-wave component has only a minuscule quantitative and no qualitative effect on the ground state.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.100.104503}, author = {Herbut, Igor F. and Boettcher, Igor and Mandal, Subrata} } @article {ISI:000473018400004, title = {Ground-state degeneracy of non-Abelian topological phases from coupled wires}, journal = {Phys. Rev. B}, volume = {99}, number = {24}, year = {2019}, month = {JUN 20}, pages = {245138}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We construct a family of two-dimensional non-Abelian topological phases from coupled wires using a non-Abelian bosonization approach. We then demonstrate how to determine the nature of the non-Abelian topological order (in particular, the anyonic excitations and the topological degeneracy on the torus) realized in the resulting gapped phases of matter. This paper focuses on the detailed case study of a coupled-wire realization of the bosonic su(2)(2) Moore-Read state, but the approach we outline here can be extended to general bosonic su(2)(k) topological phases described by non-Abelian Chern-Simons theories. We also discuss possible generalizations of this approach to the construction of three-dimensional non-Abelian topological phases.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.245138}, author = {Iadecola, Thomas and Neupert, Titus and Chamon, Claudio and Mudry, Christopher} } @article { ISI:000489036000001, title = {Heisenberg-scaling measurement protocol for analytic functions with quantum sensor networks}, journal = {Phys. Rev. A}, volume = {100}, number = {4}, year = {2019}, month = {OCT 7}, pages = {042304}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We generalize past work on quantum sensor networks to show that, for d input parameters, entanglement can yield a factor O(d) improvement in mean-squared error when estimating an analytic function of these parameters. We show that the protocol is optimal for qubit sensors, and we conjecture an optimal protocol for photons passing through interferometers. Our protocol is also applicable to continuous variable measurements, such as one quadrature of a field operator. We outline a few potential applications, including calibration of laser operations in trapped ion quantum computing.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.100.042304}, author = {Qian, Kevin and Eldredge, Zachary and Ge, Wenchao and Pagano, Guido and Monroe, Christopher and Porto, V, J. and Gorshkov, V, Alexey} } @article {ISI:000467739200016, title = {Helical Hinge Majorana Modes in Iron-Based Superconductors}, journal = {Phys. Rev. Lett.}, volume = {122}, number = {18}, year = {2019}, month = {MAY 10}, pages = {187001}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Motivated by recent experiments on FeTe1-xSex, we construct an explicit minimal model of an iron-based superconductor with band inversion at the Z point and nontopological bulk s(+/-) pairing. While there has been considerable interest in Majorana zero modes localized at vortices in such systems, we find that our model-without any vortices-intrinsically supports 1D helical Majorana modes localized at the hinges between (001) and (100) or (010) surfaces, suggesting that this is a viable platform for observing {\textquoteleft}{\textquoteleft}higher-order{{\textquoteright}{\textquoteright}} topological superconductivity. We provide a general theory for these hinge modes and discuss their stability and experimental manifestation. Our work indicates the possible experimental observability of hinge Majorana modes in iron-based topological superconductors.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.122.187001}, author = {Zhang, Rui-Xing and Cole, William S. and S. Das Sarma} } @article {ISI:000465163400005, title = {Hierarchical Majoranas in a programmable nanowire network}, journal = {Phys. Rev. B}, volume = {99}, number = {15}, year = {2019}, month = {APR 19}, pages = {155138}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We propose a hierarchical architecture for building {\textquoteleft}{\textquoteleft}logical{{\textquoteright}{\textquoteright}} Majorana zero modes using {\textquoteleft}{\textquoteleft}physical{{\textquoteright}{\textquoteright}} Majorana zero modes at the Y-junctions of a hexagonal network of semiconductor nanowires. Each Y-junction contains three {\textquoteleft}{\textquoteleft}physical{{\textquoteright}{\textquoteright}} Majoranas, which hybridize when placed in close proximity, yielding a single effective Majorana mode near zero energy. The hybridization of effective Majorana modes on neighboring Y-junctions is controlled by applied gate voltages on the links of the honeycomb network. This gives rise to a tunable tight-binding model of effective Majorana modes. We show that selecting the gate voltages that generate a Kekule vortex pattern in the set of hybridization amplitudes yields an emergent {\textquoteleft}{\textquoteleft}logical{{\textquoteright}{\textquoteright}} Majorana zero mode bound to the vortex core. The position of a logical Majorana can be tuned adiabatically, without moving any of the {\textquoteleft}{\textquoteleft}physical{{\textquoteright}{\textquoteright}} Majoranas or closing any energy gaps, by programming the values of the gate voltages to change as functions of time. A nanowire network supporting multiple such {\textquoteleft}{\textquoteleft}logical{{\textquoteright}{\textquoteright}} Majorana zero modes provides a physical platform for performing adiabatic non-Abelian braiding operations in a fully controllable manner.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.155138}, author = {Yang, Zhi-Cheng and Iadecola, Thomas and Chamon, Claudio and Mudry, Christopher} } @article { ISI:000488282800085, title = {High purity single photons entangled with an atomic qubit}, journal = {Opt. Express}, volume = {27}, number = {20}, year = {2019}, month = {SEP 30}, pages = {28143-28149}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {Trapped atomic ions are an ideal candidate for quantum network nodes, with long-lived identical qubit memories that can be locally entangled through their Coulomb interaction and remotely entangled through photonic channels. The integrity of this photonic interface is generally reliant on the purity of single photons produced by the quantum memory. Here, we demonstrate a single-photon source for quantum networking based on a trapped Ba-138(+) ion with a single photon purity of g((2))(0) = (8.1 +/- 2.3) x 10(-5) without background subtraction. We further optimize the tradeoff between the photonic generation rate and the memory-photon entanglement fidelity for the case of polarization photonic qubits by tailoring the spatial mode of the collected light. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement}, issn = {1094-4087}, doi = {10.1364/OE.27.028143}, author = {Crocker, C. and Lichtman, M. and Sosnova, K. and Carter, A. and Scarano, S. and Monroe, C.} } @article { ISI:000498883600001, title = {High-Coherence Fluxonium Qubit}, journal = {Phys. Rev. X}, volume = {9}, number = {4}, year = {2019}, month = {NOV 25}, pages = {041041}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We report superconducting fluxonium qubits with coherence times largely limited by energy relaxation and reproducibly satisfying T-2 > 100 mu s (T-2 > 400 mu s in one device). Moreover, given the state-of-the-art values of the surface loss tangent and the 1/f flux-noise amplitude, the coherence time can be further improved beyond 1 ms. Our results violate a common viewpoint that the number of Josephson junctions in a superconducting circuit-over 10(2) here-must be minimized for best qubit coherence. We outline how the unique to fluxonium combination of long coherence time and large anharmonicity can benefit both gate-based and adiabatic quantum computing.}, issn = {2160-3308}, doi = {10.1103/PhysRevX.9.041041}, author = {Nguyen, Long B. and Lin, Yen-Hsiang and Somoroff, Aaron and Mencia, Raymond and Grabon, Nicholas and Manucharyan, Vladimir E.} } @article {15801, title = {Higher-Order Topology and Nodal Topological Superconductivity in Fe(Se,Te) Heterostructures}, journal = {Phys. Rev. Lett.}, volume = {123}, year = {2019}, month = {Oct}, pages = {167001}, doi = {10.1103/PhysRevLett.123.167001}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.123.167001}, author = {Zhang, Rui-Xing and Cole, William S. and Wu, Xianxin and S Das Sarma} } @article { ISI:000496923500007, title = {High-precision measurement and ab initio calculation of the (6s(2)6p(2)) P-3(0) -> P-3(2) electric-quadrupole-transition amplitude in Pb-208}, journal = {Phys. Rev. A}, volume = {100}, number = {5}, year = {2019}, month = {NOV 18}, pages = {052506}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We have completed a measurement of the (6s(2)6p(2)) P-3(0) -> P-3(2) 939 nm electric quadrupole (E2) transition amplitude in atomic lead. Using a Faraday rotation spectroscopy technique and a sensitive polarimeter, we have measured this very weak E2 transition, and determined its amplitude to be < P-3(2) parallel to Q parallel to P-3(0)> = 8.91(9) a.u. We also present an ab initio theoretical calculation of this matrix element, determining its value to be 8.86(5) a.u., which is in excellent agreement with the experimental result. We heat a quartz vapor cell containing Pb-208 to between 800 and 940 degrees C, apply a similar to 10 G longitudinal magnetic field, and use polarization modulation and lock-in detection to measure optical rotation amplitudes of order 1 mrad with noise near 1 mu rad. We compare the Faraday rotation amplitude of the E2 transition to that of the P-3(0)-P-3(1) 1279 nm magnetic dipole (M1) transition under identical sample conditions.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.100.052506}, author = {Maser, Daniel L. and Hoenig, Eli and Wang, B-Y and Rupasinghe, P. M. and Porsev, S. G. and Safronova, M. S. and Majumder, P. K.} } @article {ISI:000465439100022, title = {Hot electron heatsinks for microwave attenuators below 100 mK}, journal = {Appl. Phys. Lett.}, volume = {114}, number = {15}, year = {2019}, month = {APR 15}, pages = {152602}, publisher = {AMER INST PHYSICS}, type = {Article}, abstract = {We demonstrate improvements to the cooling power of broad bandwidth (10 GHz) microwave attenuators designed for operation at temperatures below 100 mK. By interleaving 9-mu m thick conducting copper heatsinks in between 10-mu m long, 70-nm thick resistive nichrome elements, the electrical heat generated in the nichrome elements is conducted more readily into the heatsinks, effectively decreasing the thermal resistance between the hot electrons and cold phonons. For a 20 dB attenuator mounted at 20 mK, a minimum noise temperature of T-n similar to 50 mK was obtained for small dissipated powers (P-d < 1 nW) in the attenuator. For higher dissipated powers, we find T-n proportional to P-d(1/4.4), with P-d = 100 nW corresponding to a noise temperature of 90 mK. This is in good agreement with thermal modeling of the system and represents nearly a factor of 20 improvement in cooling power or a factor of 1.8 reduction in T-n for the same dissipated power, when compared to a previous design without interleaved heatsinks. Published under license by AIP Publishing.}, issn = {0003-6951}, doi = {10.1063/1.5097369}, author = {Yeh, Jen-Hao and Huang, Yizhou and Zhang, Rui and Premaratne, Shavindra and LeFebvre, Jay and Wellstood, F. C. and Palmer, B. S.} } @article {ISI:000473755200026, title = {Hyperbolic lattices in circuit quantum electrodynamics}, journal = {Nature}, volume = {571}, number = {7763}, year = {2019}, month = {JUL 4}, pages = {45+}, publisher = {NATURE PUBLISHING GROUP}, type = {Article}, abstract = {After two decades of development, cavity quantum electrodynamics with superconducting circuits has emerged as a rich platform for quantum computation and simulation. Lattices of coplanar waveguide resonators constitute artificial materials for microwave photons, in which interactions between photons can be incorporateded either through the use of nonlinear resonator materials or through coupling between qubits and resonators. Here we make use of the previously overlooked property that these lattice sites are deformable and permit tight-binding lattices that are unattainable even in solid-state systems. We show that networks of coplanar waveguide resonators can create a class of materials that constitute lattices in an effective hyperbolic space with constant negative curvature. We present numerical simulations of hyperbolic analogues of the kagome lattice that show unusual densities of states in which a macroscopic number of degenerate eigenstates comprise a spectrally isolated flat band. We present a proof-of-principle experimental realization of one such lattice. This paper represents a step towards on-chip quantum simulation of materials science and interacting particles in curved space.}, issn = {0028-0836}, doi = {10.1038/s41586-019-1348-3}, author = {Kollar, Alicia J. and Fitzpatrick, Mattias and Houck, Andrew A.} } @article { ISI:000493335100001, title = {Identification of advanced spin-driven thermoelectric materials via interpretable machine learning}, journal = {npj Comput. Mater.}, volume = {5}, year = {2019}, month = {OCT 30}, pages = {103}, publisher = {SPRINGERNATURE}, type = {Article}, abstract = {Machine learning is becoming a valuable tool for scientific discovery. Particularly attractive is the application of machine learning methods to the field of materials development, which enables innovations by discovering new and better functional materials. To apply machine learning to actual materials development, close collaboration between scientists and machine learning tools is necessary. However, such collaboration has been so far impeded by the black box nature of many machine learning algorithms. It is often difficult for scientists to interpret the data-driven models from the viewpoint of material science and physics. Here, we demonstrate the development of spin-driven thermoelectric materials with anomalous Nernst effect by using an interpretable machine learning method called factorized asymptotic Bayesian inference hierarchical mixture of experts (FAB/HMEs). Based on prior knowledge of material science and physics, we were able to extract from the interpretable machine learning some surprising correlations and new knowledge about spin-driven thermoelectric materials. Guided by this, we carried out an actual material synthesis that led to the identification of a novel spin-driven thermoelectric material. This material shows the largest thermopower to date.}, issn = {2057-3960}, doi = {10.1038/s41524-019-0241-9}, author = {Iwasaki, Yuma and Sawada, Ryohto and Stanev, Valentin and Ishida, Masahiko and Kirihara, Akihiro and Omori, Yasutomo and Someya, Hiroko and Takeuchi, Ichiro and Saitoh, Eiji and Yorozu, Shinichi} } @article {ISI:000473013000002, title = {Identification of superconducting pairing symmetry in twisted bilayer graphene using in-plane magnetic field and strain}, journal = {Phys. Rev. B}, volume = {99}, number = {22}, year = {2019}, month = {JUN 25}, pages = {220507}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We show how the pairing symmetry of superconducting states in twisted bilayer graphene can be experimentally identified by theoretically studying effects of externally applied in-plane magnetic field and strain. In the low-field regime, superconducting critical temperature T-c is suppressed by in-plane magnetic field B-parallel to in singlet channels, but is enhanced by weak B-parallel to in triplet channels, providing an important distinction. The in-plane angular dependence of the critical B-parallel to,B-c has a sixfold rotational symmetry, which is broken when strain is present. We show that anisotropy in B-parallel to,B-c generated by strain can be similar for s- and d-wave channels in moire superlattices. The d-wave state is pinned to be nematic by strain and consequently gapless, which is distinguishable from the fully gapped s-wave state by tunneling gap measurements.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.220507}, author = {Wu, Fengcheng and S. Das Sarma} } @article {ISI:000467473500012, title = {Imaging topology of Hofstadter ribbons}, journal = {New J. Phys.}, volume = {21}, year = {2019}, month = {MAY 8}, pages = {053021}, publisher = {IOP PUBLISHING LTD}, type = {Article}, abstract = {Physical systems with non-trivial topological order find direct applications in metrology (Klitzing et al 1980 Phys. Rev. Lett. 45 494-7) and promise future applications in quantum computing (Freedman 2001 Found. Comput. Math. 1 183-204; Kitaev 2003 Ann. Phys. 303 2-30). The quantum Hall effect derives from transverse conductance, quantized to unprecedented precision in accordance with the system{\textquoteright}s topology (Laughlin 1981 Phys. Rev. B 23 5632-33). At magnetic fields beyond the reach of current condensed matter experiment, around 10(4)T, this conductance remains precisely quantized with values based on the topological order (Thouless et al 1982 Phys. Rev. Lett. 49 405-8). Hitherto, quantized conductance has only been measured in extended 2D systems. Here, we experimentally studied narrow 2D ribbons, just 3 or 5 sites wide along one direction, using ultracold neutral atoms where such large magnetic fields can be engineered (Jaksch and Zoller 2003 New J. Phys. 5 56; Miyake et al 2013 Phys. Rev. Lett. 111 185302; Aidelsburger et al 2013 Phys. Rev. Lett. 111 185301; Celi et al 2014 Phys. Rev. Lett. 112 043001; Stuhl et al 2015 Science 349 1514; Mancini et al 2015 Science 349 1510; An et al 2017 Sci. Adv. 3). We microscopically imaged the transverse spatial motion underlying the quantized Hall effect. Our measurements identify the topological Chern numbers with typical uncertainty of 5\%, and show that although band topology is only properly defined in infinite systems, its signatures are striking even in nearly vanishingly thin systems.}, keywords = {quantum Hall effect, quantum simulation, quantum transport, ultracold atoms}, issn = {1367-2630}, doi = {10.1088/1367-2630/ab165b}, author = {Genkina, Dina and Aycock, Lauren M. and Lu, I, Hsin- and Lu, Mingwu and Pineiro, Alina M. and Spielman, I. B.} } @article {ISI:000455683000004, title = {Implementation of a generalized controlled-NOT gate between fixed-frequency transmons}, journal = {Phys. Rev. A}, volume = {99}, number = {1}, year = {2019}, month = {JAN 11}, pages = {012317}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We have embedded two fixed-frequency Al/AlOx/Al transmons, with ground-to-excited transition frequencies at 6.0714 and 6.7543 GHz, in a single three-dimensional Al cavity with a fundamental mode at 7.7463 GHz. Strong coupling between the cavity and each transmon results in an effective qubit-qubit coupling strength of 26 MHz and a -1 MHz dispersive shift in each qubit{\textquoteright}s transition frequency, depending on the state of the other qubit. Using the all-microwave SWIPHT (speeding up wave forms by inducing phases to harmful transitions) technique {[}Economou and Barnes, Phys. Rev. B 91, 161405 (2015)], we demonstrate the operation of a generalized controlled-NOT gate between the two qubits, with a gate time of tau(g) = 907 ns optimized for this device. Using quantum process tomography we find that the gate fidelity is 83-84\%, somewhat less than the 87\% fidelity expected from relaxation and dephasing in the transmons during the gate time.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.99.012317}, author = {Premaratne, Shavindra P. and Yeh, Jen-Hao and Wellstood, F. C. and Palmer, B. S.} } @article {ISI:000459579600002, title = {Incorporation of random alloy GaBixAs1-x barriers in InAs quantum dot molecules: Energy levels and confined hole states}, journal = {Phys. Rev. B}, volume = {99}, number = {7}, year = {2019}, month = {FEB 22}, pages = {075308}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Self-assembled InAs quantum dots (QDs), which have long hole-spin coherence times and are amenable to optical control schemes, have long been explored as building blocks for qubit architectures. One such design consists of vertically stacking two QDs to create a QD molecule (QDM) and using the spin-mixing properties of {\textquoteleft}{\textquoteleft}moleculelike{{\textquoteright}{\textquoteright}} coupled hole states for all-optical qubit manipulation. In this paper, the first of two papers, we introduce the incorporation of dilute GaBixAs1-x alloys in the barrier region between the two dots. GaBixAs1-x is expected to increase the spin mixing of the molecular states needed for qubit operations by raising the barrier valence-band edge and spin-orbit splitting. Using an atomistic tight-binding model, we compute the properties of GaBixAs1-x and the modification of hole states that arise when the alloy is used in the barrier of an InAs QDM. An atomistic treatment is necessary to correctly capture nontraditional alloy effects such as the band-anticrossing valence band. It also allows for the study of configurational variances and clustering effects of the alloy. We find that in InAs QDMs with a GaBiAs interdot barrier, electron states are not strongly affected by the inclusion of Bi. However, hole states are much more sensitive to the presence and configuration of Bi in the barriers. By independently studying the alloy-induced strain and electronic scattering off Bi and As orbitals, we conclude that an initial increase in QDM hole-state energy at low Bi concentration is caused by the alloy-induced strain. We further find that the decrease in QDM hole energy at higher Bi concentrations can only be explained when both alloy strain and orbital effects are considered. In our second paper, we use the understanding developed here to discuss how the alloyed barriers contribute to enhancement in hole spin-mixing and the implications for QDM qubit architectures.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.075308}, author = {Lin, Arthur and Doty, Matthew F. and Bryant, Garnett W.} } @article { ISI:000490353500059, title = {Indistinguishable Photons from Deterministically Integrated Single Quantum Dots in Heterogeneous GaAs/Si3N4 Quantum Photonic Circuits}, journal = {Nano Lett.}, volume = {19}, number = {10}, year = {2019}, month = {OCT}, pages = {7164-7172}, publisher = {AMER CHEMICAL SOC}, type = {Article}, abstract = {Silicon photonics enables scaling of quantum photonic systems by allowing the creation of extensive, low-loss, reconfigurable networks linking various functional on-chip elements. Inclusion of single quantum emitters onto photonic circuits, acting as on-demand sources of indistinguishable photons or single-photon nonlinearities, may enable large-scale chip-based quantum photonic circuits and networks. Toward this, we use low-temperature in situ electron-beam lithography to deterministically produce hybrid GaAs/Si3N4 photonic devices containing single InAs quantum dots precisely located inside nanophotonic structures, which act as efficient, Si3N4 waveguide-coupled on-chip, on-demand single-photon sources. The precise positioning afforded by our scalable fabrication method furthermore allows observation of postselected indistinguishable photons. This indicates a promising path toward significant scaling of chip-based quantum photonics, enabled by large fluxes of indistinguishable single-photons produced on-demand, directly on-chip.}, keywords = {deterministic sample fabrication, hybrid devices, indistinguishable photons, Quantum Dots, Quantum optics}, issn = {1530-6984}, doi = {10.1021/acs.nanolett.9b02758}, author = {Schnauber, Peter and Singh, Anshuman and Schall, Johannes and Park, Suk In and Song, Jin Dong and Rodt, Sven and Srinivasan, Kartik and Reitzenstein, Stephan and Davanco, Marcelo} } @conference {ISI:000482226301193, title = {Integration of Quantum Emitters with Lithium Niobate Photonics}, booktitle = {2019 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO)}, series = {Conference on Lasers and Electro-Optics}, year = {2019}, note = {Conference on Lasers and Electro-Optics (CLEO), San Jose, CA, MAY 05-10, 2019}, publisher = {IEEE; AdValue Photon; Amer Elements; Class5 Photon; Coherent; GoFoton; Light Convers; LightTrans; MKS; OZ Opt Online; Santec; ThorLabs; UQDevices; YSL Photon}, organization = {IEEE; AdValue Photon; Amer Elements; Class5 Photon; Coherent; GoFoton; Light Convers; LightTrans; MKS; OZ Opt Online; Santec; ThorLabs; UQDevices; YSL Photon}, type = {Proceedings Paper}, abstract = {We demonstrate integration of telecom quantum dots with lithium niobate photonics using a pick-and-place technique. Second order photon correlation measurement performed with an on-chip beamsplitter confirms the single-photon nature of the emission. (C) 2019 The Author(s)}, isbn = {978-1-943580-57-6}, issn = {2160-9020}, author = {Aghaeimeibodi, Shahriar and Desiatov, Boris and Kim, Je-Hyung and Lee, Chang-Min and Buyukkaya, Mustafa Atabey and Karasahin, Aziz and Richardson, Christopher J. K. and Leavitt, Richard P. and Loncar, Marko and Waks, Edo} } @article { ISI:000457704900001, title = {Interacting Qubit-Photon Bound States with Superconducting Circuits}, journal = {PHYSICAL REVIEW X}, volume = {9}, number = {1}, year = {2019}, month = {FEB 1}, pages = {011021}, issn = {2160-3308}, doi = {10.1103/PhysRevX.9.011021}, author = {Sundaresan, Neereja M. and Lundgren, Rex and Zhu, Guanyu and Gorshkov, V, Alexey and Houck, Andrew A.} } @article {ISI:000469902700001, title = {Interaction-induced transition in the quantum chaotic dynamics of a disordered metal}, journal = {Ann. Phys.}, volume = {405}, year = {2019}, month = {JUN}, pages = {1-13}, publisher = {ACADEMIC PRESS INC ELSEVIER SCIENCE}, type = {Article}, abstract = {We demonstrate that a weakly disordered metal with short-range interactions exhibits a transition in the quantum chaotic dynamics when changing the temperature or the interaction strength. For weak interactions, the system displays exponential growth of the out-of-time-ordered correlator (OTOC) of the current operator. The Lyapunov exponent of this growth is temperature-independent in the limit of vanishing interaction. With increasing the temperature or the interaction strength, the system undergoes a transition to a non-chaotic behaviour, for which the exponential growth of the OTOC is absent. We conjecture that the transition manifests itself in the quasiparticle energy-level statistics and also discuss ways of its explicit observation in cold-atom setups. (C) 2019 Elsevier Inc. All rights reserved.}, issn = {0003-4916}, doi = {10.1016/j.aop.2019.03.008}, author = {Syzranov, V, S. and Gorshkov, V, A. and Galitski, V. M.} } @article {14826, title = {Interference of Temporally Distinguishable Photons Using Frequency-Resolved Detection}, journal = {Phys. Rev. Lett.}, volume = {123}, year = {2019}, month = {Sep}, pages = {123603}, doi = {10.1103/PhysRevLett.123.123603}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.123.123603}, author = {Orre, Venkata Vikram and Goldschmidt, Elizabeth A. and Deshpande, Abhinav and Gorshkov, Alexey V. and Tamma, Vincenzo and Hafezi, Mohammad and Mittal, Sunil} } @article {ISI:000467378000002, title = {Interplay between magnetic and vestigial nematic orders in the layered J(1)-J(2) classical Heisenberg model}, journal = {Phys. Rev. B}, volume = {99}, number = {17}, year = {2019}, month = {MAY 6}, pages = {174404}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study the layered J(1)-J(2) classical Heisenberg model on the square lattice using a self-consistent bond theory. We derive the phase diagram for fixed J(1) as a function of temperature T, J(2), and interplane coupling J(z). Broad regions of (anti)ferromagnetic and stripe order are found, and are separated by a first-order transition near J(2) approximate to 0.5 (in units of vertical bar J(1)vertical bar). Within the stripe phase the magnetic and vestigial nematic transitions occur simultaneously in first-order fashion for strong J(z). For weaker J(z), there is in addition, for J(2){*} < J(2) < J(2){*}{*}, an intermediate regime of split transitions implying a finite temperature region with nematic order but no long-range stripe magnetic order. In this split regime, the order of the transitions depends sensitively on the deviation from J(2){*} and J(2){*}{*}, with split second-order transitions predominating for J(2){*} << J(2) << J(2){*}{*}. We find that the value of J(2){*} depends weakly on the interplane coupling and is just slightly larger than 0.5 for vertical bar J(z)vertical bar less than or similar to 0.01. In contrast, the value of J(2){*}{*} increases quickly from J(2){*} at vertical bar J(z)vertical bar less than or similar to 0.01 as the interplane coupling is further reduced. In addition, the magnetic correlation length is shown to directly depend on the nematic order parameter and thus exhibits a sharp increase (or jump) upon entering the nematic phase. Our results are broadly consistent with the predictions based on itinerant electron models of the iron-based superconductors in the normal state and, thus, help substantiate a classical spin framework for providing a phenomenological description of their magnetic properties.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.174404}, author = {Syljuasen, Olav F. and Paaske, Jens and Schecter, Michael} } @article { ISI:000459554300005, title = {Large stark tuning of InAs/InP quantum dots}, journal = {APPLIED PHYSICS LETTERS}, volume = {114}, number = {7}, year = {2019}, month = {FEB 18}, pages = {071105}, issn = {0003-6951}, doi = {10.1063/1.5082560}, author = {Aghaeimeibodi, Shahriar and Lee, Chang-Min and Buyukkaya, Mustafa Atabey and Richardson, Christopher J. K. and Waks, Edo} } @article {ISI:000457732400003, title = {Linear-in-T resistivity in dilute metals: A Fermi liquid perspective}, journal = {Phys. Rev. B}, volume = {99}, number = {8}, year = {2019}, month = {FEB 4}, pages = {085105}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We consider a short-range deformation-potential scattering model of electron-acoustic phonon interaction to calculate the resistivity of an ideal metal (i.e., no other scattering mechanism except acoustic phonon scattering) as a function of temperature (T) and electron density (n). The resistivity calculation is based on the Boltzmann transport theory within the relaxation-time approximation in the nearly-free-electron single-band approximation. We consider both 3D metals and 2D metals and focus on the dilute limit, i.e., low effective metallic carrier density (and hence low effective Fermi wave number k(F)) of the system. The main findings are (1) a phonon-scattering-induced linear-in-T resistivity could persist to arbitrarily low temperatures in the dilute limit independent of the Debye temperature (T-D), although, eventually, the low-T resistivity turns over to the expected Bloch-Grfineisen (BG) behavior with T-5(T-4) dependence, in 3D (2D), respectively, with the crossover temperature, T-BG, from the linear-in-T to the BG behavior, being proportional to the Fermi momentum, is small in the dilute limit; (2) because of low values of n, the phonon-induced resistivity could be very high in the system, orders of magnitude above the corresponding room temperature resistivity of ordinary metals; and (3) the resistivity shows an intrinsic saturation effect at very high temperatures (for T > T-D) and, in fact, weakly decreases with increasing T above a high crossover temperature with this crossover being dependent on both T-D and n in a nonuniversal manner-this high-temperature crossover is not directly connected with the Mott-Ioffe-Regel limit and is a reflection of phonon phase-space restriction. We discuss the qualitative trends in the resistivity as a function of temperature, density, phonon velocity, and system dimensionality. We also provide {\textquoteleft}{\textquoteleft}high-temperature{{\textquoteright}{\textquoteright}} linear-in-T resistivity results for 2D and 3D Dirac materials. Our work brings out the universal features of phonon-induced transport in dilute metals, and we comment on possible implications of our results for strange metals, emphasizing that the mere observation of a linear-in-T metallic resistivity at low temperatures or a very high metallic resistivity at high temperatures is not necessarily a reason to invoke an underlying quantum critical strange-metal behavior. Dilute metals may very well have highly unusual (compared with normal metals) transport properties arising from quantitative, but not qualitatively new, underlying physics. We discuss the temperature variation of the effective transport scattering rate showing that, for reasonable parameters, the scattering rate could be below or above k(B)T and, in particular, purely coincidentally, the calculated scattering rate happens to be k(B)T in normal metals with no implications whatsoever for the so-called Planckian behavior. Our work manifestly establishes that an apparent Planckian dissipative behavior could arise from the usual electron-phonon interaction without implying any strange metallicity or a failure of the quasiparticle paradigm in contrast to recent claims.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.085105}, author = {Hwang, E. H. and S. Das Sarma} } @article {ISI:000474892400001, title = {Locality and Digital Quantum Simulation of Power-Law Interactions}, journal = {Phys. Rev. X}, volume = {9}, number = {3}, year = {2019}, month = {JUL 10}, pages = {031006}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The propagation of information in nonrelativistic quantum systems obeys a speed limit known as a Lieb-Robinson bound. We derive a new Lieb-Robinson bound for systems with interactions that decay with distance r as a power law, 1/r(alpha). The bound implies an effective light cone tighter than all previous bounds. Our approach is based on a technique for approximating the time evolution of a system, which was first introduced as part of a quantum simulation algorithm by Haah et al., FOCS{\textquoteright} 18. To bound the error of the approximation, we use a known Lieb-Robinson bound that is weaker than the bound we establish. This result brings the analysis full circle, suggesting a deep connection between Lieb-Robinson bounds and digital quantum simulation. In addition to the new Lieb-Robinson bound, our analysis also gives an error bound for the Haah et al. quantum simulation algorithm when used to simulate power-law decaying interactions. In particular, we show that the gate count of the algorithm scales with the system size better than existing algorithms when alpha > 3D (where D is the number of dimensions).}, issn = {2160-3308}, doi = {10.1103/PhysRevX.9.031006}, author = {Tran, Minh C. and Guo, Andrew Y. and Su, Yuan and Garrison, James R. and Eldredge, Zachary and Foss-Feig, Michael and Childs, Andrew M. and Gorshkov, Alexey V.} } @article { ISI:000456992300001, title = {Machine learning techniques for state recognition and auto-tuning in quantum dots}, journal = {NPJ QUANTUM INFORMATION}, volume = {5}, year = {2019}, month = {JAN 21}, pages = {6}, issn = {2056-6387}, doi = {10.1038/s41534-018-0118-7}, author = {Kalantre, Sandesh S. and Zwolak, Justyna P. and Ragole, Stephen and Wu, Xingyao and Zimmerman, Neil M. and Stewart, Jr., M. D. and Taylor, Jacob M.} } @article { ISI:000503808100004, title = {Manifestations of spin-orbit coupling in a cuprate superconductor}, journal = {Phys. Rev. B}, volume = {100}, number = {22}, year = {2019}, month = {DEC 20}, pages = {224512}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Exciting new work on Bi2Sr2CaCu2O8+delta (Bi2212) shows the presence of nontrivial spin-orbit coupling effects as seen in spin-resolved angle-resolved photoemission spectroscopy data {[}K. Gotlieb et al., Science 362, 1271 (2018)]. Motivated by these observations we consider how the picture of spin-orbit coupling through local inversion symmetry breaking might be observed in cuprate superconductors. Furthermore, we examine two spin-orbit driven effects, the spin-Hall effect and the Edelstein effect, focusing on the details of their realizations within both the normal and superconducting states.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.100.224512}, author = {Raines, Zachary M. and Allocca, Andrew A. and Galitski, Victor M.} } @article { ISI:000501342800003, title = {Measurement of the 7p P-2(3/2) state branching fractions in Ra+}, journal = {Phys. Rev. A}, volume = {100}, number = {6}, year = {2019}, month = {DEC 6}, pages = {062504}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We report a measurement of the radium ion{\textquoteright}s 7p(2)P(3/2) state branching fractions and improved theoretical calculations. With a single laser-cooled Ra-226(+) ion we measure the P-3/2 branching fractions to the 7s(2)S(1/2) ground state 0.876 78(20), the 6d D-2(5/2) state 0.107 59(10), and the 6d D-2(3/2) state 0.015 63(21).}, issn = {2469-9926}, doi = {10.1103/PhysRevA.100.062504}, author = {Fan, M. and Holliman, C. A. and Porsev, S. G. and Safronova, M. S. and Jayich, A. M.} } @article {ISI:000469016300011, title = {Measurement-induced dynamics and stabilization of spinor-condensate domain walls}, journal = {Phys. Rev. A}, volume = {99}, number = {5}, year = {2019}, month = {MAY 22}, pages = {053612}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Weakly measuring many-body systems and allowing for feedback in real time can simultaneously create and measure new phenomena in quantum systems. We theoretically study the dynamics of a continuously measured two-component Bose-Einstein condensate (BEC) potentially containing a domain wall and focus on the tradeoff between usable information obtained from measurement and quantum backaction. Each weakly measured system yields a measurement record from which we extract real-time dynamics of the domain wall. We show that quantum backaction due to measurement causes two primary effects: domain-wall diffusion and overall heating. The system dynamics and signal-to-noise ratio depend on the choice of measurement observable. We propose a feedback protocol to dynamically create a stable domain wall in the regime where domain walls are unstable, giving a prototype example of Hamiltonian engineering using measurement and feedback.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.99.053612}, author = {Hurst, Hilary M. and Spielman, I. B.} } @article {ISI:000483578600012, title = {Measurements of the branching ratios for 6P(1/2) decays in Ba-138(+)}, journal = {Phys. Rev. A}, volume = {100}, number = {3}, year = {2019}, month = {SEP 3}, pages = {032503}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Measurement of the branching ratios for 6P(1/2) decays to 6S(1/2) and 5D(3/2) in Ba-138(+) are reported with the decay probability from 6P(1/2) to 5D(3/2) measured to be p = 0.268177 +/- (37)(stat)-(20)(sys). This result differs from a recent report by 12 sigma. A detailed account of systematics is given, and the likely source of the discrepancy is identified. The new value of the branching reported here is combined with previous experimental results to give a new estimate of tau = 7.855(10) ns for the 6P(1/2) lifetime. In addition, ratios of matrix elements calculated from theory are combined with experimental results to provide improved theoretical estimates of the 6P(3/2) lifetime and the associated matrix elements.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.100.032503}, author = {Arnold, K. J. and Chanu, S. R. and Kaewuam, R. and Tan, T. R. and Yeo, L. and Zhang, Zhiqiang and Safronova, M. S. and Barrett, M. D.} } @article {ISI:000466709400015, title = {Microcontroller based scanning transfer cavity lock for long-term laser frequency stabilization}, journal = {Rev. Sci. Instrum.}, volume = {90}, number = {4}, year = {2019}, month = {APR}, pages = {043115}, publisher = {AMER INST PHYSICS}, type = {Article}, abstract = {We present a compact all-digital implementation of a scanning transfer cavity lock (STCL) for long-term laser frequency stabilization. An interrupt-driven state machine is employed to realize the STCL with the capability to correct for frequency drifts in the slave laser frequency due to measured changes in the lab environmental conditions. We demonstrate an accuracy of 0.9 MHz for master laser and slave laser wavelengths of 556 nm and 798 nm as an example. The slave laser is also demonstrated to dynamically scan over a wide frequency range while retaining its lock, allowing us to accurately interrogate atomic transitions. Published under license by AIP Publishing.}, issn = {0034-6748}, doi = {10.1063/1.5067266}, author = {Subhankar, S. and Restelli, A. and Wang, Y. and Rolston, S. L. and Porto, J. V.} } @article { ISI:000504926700014, title = {Milliwatt-threshold visible-telecom optical parametric oscillation using silicon nanophotonics}, journal = {Optica}, volume = {6}, number = {12}, year = {2019}, month = {DEC 20}, pages = {1535-1541}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {The on-chip creation of coherent light at visible wavelengths is crucial to field-level deployment of spectroscopy and metrology systems. Although on-chip lasers have been implemented in specific cases, a general solution that is not restricted by limitations of specific gain media has not been reported, to the best of our knowledge. Here, we propose creating visible light from an infrared pump by widely separated optical parametric oscillation (OPO) using silicon nanophotonics. The OPO creates signal and idler light in the 700 nm and 1300 nm bands, respectively, with a 900 nm pump. It operates at a threshold power of (0.9 +/- 0.1) mW, over 50 x smaller than other widely separated microcavity OPO works, which have been reported only in the infrared. This low threshold enables direct pumping without need of an intermediate optical amplifier. We further show how the device design can be modified to generate 780 nm and 1500 nm light with a similar power efficiency. Our nanophotonic OPO shows distinct advantages in power efficiency, operation stability, and device scalability, and is a major advance towards flexible on-chip generation of coherent visible light.}, issn = {2334-2536}, doi = {10.1364/OPTICA.6.001535}, author = {Lu, Xiyuan and Moille, Gregory and Singh, Anshuman and Li, Qing and Westly, Daron A. and Rao, Ashutosh and Yu, Su-Peng and Briles, Travis C. and Papp, Scott B. and Srinivasan, Kartik} } @article { ISI:000502782600002, title = {Momentum-space entanglement after a quench in one-dimensional disordered fermionic systems}, journal = {Phys. Rev. B}, volume = {100}, number = {24}, year = {2019}, month = {DEC 13}, pages = {241108}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We numerically investigate the momentum-space entanglement entropy and entanglement spectrum of the random-dimer model and its generalizations, which circumvent Anderson localization, after a quench in the Hamiltonian parameters. The type of dynamics that occurs depends on whether or not the Fermi level of the initial state is near the energy of the delocalized states present in these models. If the Fermi level of the initial state is near the energy of the delocalized states, we observe an interesting slow logarithmiclike growth of the momentum-space entanglement entropy followed by an eventual saturation. Otherwise, the momentum-space entanglement entropy is found to rapidly saturate. We also find that the momentum-space entanglement spectrum reveals the presence of delocalized states in these models for long times after the quench and the many-body entanglement gap decays logarithmically in time when the Fermi level is near the energy of the delocalized states.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.100.241108}, author = {Lundgren, Rex and Liu, Fangli and Laurell, Pontus and Fiete, Gregory A.} } @article { ISI:000504573300001, title = {A multiwell applicator for conformal brachytherapy of superficial skin tumors: A simulation study}, journal = {Skin Res. Technol.}, year = {2019}, month = {DEC 27}, publisher = {WILEY}, type = {Article; Early Access}, abstract = {Background Brachytherapy of thin skin tumors using beta particles can protect underlying sensitive structures such as the bone because of the rapid dose falloff of this type of radiation in tissue. The current work describes a skin brachytherapy applicator, based on beta radiation, that can provide the needed cell-killing radiation dose matched to the shape of individual skin tumors. Materials and methods The applicator and its template were fabricated using 3D printing technology. Any clinically approved beta-emitting isotope in the form of a radioactive gel could theoretically be used in this applicator. Monte Carlo simulations were employed to study the capability of the applicator in conforming dose distribution based on the shape of the tumor. Dose profile in the shallow depth, transverse dose profiles at different depths, and the percent depth dose from this applicator were calculated. The radioisotope of choice for our calculations was Yttrium-90 (Y-90). Results Using the proposed applicator, it is possible to create a desired dose profile matching the tumor surface shape. Conclusion The short-range of the beta radiation, together with the dose conforming capability of the applicator, may lead to minimal interactions with the healthy tissue around the skin lesion.}, keywords = {3D printing technology, beta particles, beta-emitting isotopes, brachytherapy, Monte Carlo methods, skin tumor, Y-90}, issn = {0909-752X}, doi = {10.1111/srt.12826}, author = {Pashazadeh, Ali and Robatjazi, Mostafa and Castro, Nathan J. and Friebe, Michael} } @article {14436, title = {Nanoscale Atomic Density Microscopy}, journal = {Phys. Rev. X}, volume = {9}, year = {2019}, month = {Apr}, pages = {021002}, doi = {10.1103/PhysRevX.9.021002}, url = {https://link.aps.org/doi/10.1103/PhysRevX.9.021002}, author = {Subhankar, S. and Wang, Y. and Tsui, T-C. and Rolston, S. L. and Porto, J. V.} } @article {ISI:000485768100009, title = {Narrow-line Cooling and Determination of the Magic Wavelength of Cd}, journal = {Phys. Rev. Lett.}, volume = {123}, number = {11}, year = {2019}, month = {SEP 13}, pages = {113201}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We experimentally and theoretically determine the magic wavelength of the (5s(2))S-1(0) - (5s5p)P-3(0) clock transition of Cd-111 to be 419.88(14) and 420.1(7) nm. To perform Lamb-Dicke spectroscopy of the clock transition, we use narrow-line laser cooling on the S-1(0) - P-3(1) transition to cool the atoms to 6 mu K and load them into an optical lattice. Cadmium is an attractive candidate for optical lattice clocks because it has a small sensitivity to blackbody radiation and its efficient narrow-line cooling mitigates higher order light shifts. We calculate the blackbody shift, including the dynamic correction, to be fractionally 2.83(8) x 10(-16) at 300 K, an order of magnitude smaller than that of Sr and Yb. We also report calculations of the Cd P-1(1) lifetime and the ground state C-6 coefficient.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.123.113201}, author = {Yamaguchi, A. and Safronova, M. S. and Gibble, K. and Katori, H.} } @article {ISI:000456484300001, title = {Neutral-Atom Wavelength-Compatible 780 nm Single Photons from a Trapped Ion via Quantum Frequency Conversion}, journal = {Phys. Rev. Appl.}, volume = {11}, number = {1}, year = {2019}, month = {JAN 23}, pages = {014044}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The interfacing of quantum platforms via photonic links is a precursor for establishing scalable quantum networks. The connection of different types of quantum memories for hybrid networking requires the overcoming of the disparate photon wavelengths emitted by each quantum memory. Given achievements in quantum information processing with trapped-ion and neutral-atom architectures, a hybrid system with modular interconnectivity is advantageous. Here, we use a trapped Ba-138(+) ion and a periodically poled lithium-niobate (PPLN) waveguide, with a fiber-coupled output, to demonstrate 19\% end-to-end efficient quantum frequency conversion (QFC) of single photons from 493 to 780 nm and use fluorescence of the ion to produce light at the Rb-87 D-2 transition wavelength. To demonstrate the quantum nature of both the unconverted 493 nm photons and the converted photons near 780 nm, we observe strong quantum statics in their respective second-order intensity correlations. This work extends the range of intralaboratory networking between ions and networking between disparate quantum memories.}, issn = {2331-7019}, doi = {10.1103/PhysRevApplied.11.014044}, author = {Siverns, James D. and Hannegan, John and Quraishi, Qudsia} } @article { ISI:000502040000002, title = {Next-generation crossover-free quantum Hall arrays with superconducting interconnections}, journal = {Metrologia}, volume = {56}, number = {6}, year = {2019}, month = {DEC}, pages = {065002}, publisher = {IOP PUBLISHING LTD}, type = {Article}, abstract = {This work presents precision measurements of quantized Hall array resistance devices using superconducting, crossover-free and multiple interconnections as well as graphene split contacts. These new techniques successfully eliminate the accumulation of internal resistances and leakage currents that typically occur at interconnections and crossing leads between interconnected devices. As a result, a scalable quantized Hall resistance array is obtained with a nominal value that is as precise and stable as that from single-element quantized Hall resistance standards.}, keywords = {epitaxial graphene, multiple connection, quantized Hall array resistance standards, quantum Hall effect, split contacts, superconducting contacts}, issn = {0026-1394}, doi = {10.1088/1681-7575/ab3ba3}, author = {Kruskopf, Mattias and Rigosi, Albert F. and Panna, Alireza R. and Marzano, Martina and Patel, Dinesh and Jin, Hanbyul and Newell, David B. and Elmquist, Randolph E.} } @article { ISI:000498063400002, title = {Nondestructive Cooling of an Atomic Quantum Register via State-Insensitive Rydberg Interactions}, journal = {Phys. Rev. Lett.}, volume = {123}, number = {21}, year = {2019}, month = {NOV 20}, pages = {213603}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We propose a protocol for sympathetically cooling neutral atoms without destroying the quantum information stored in their internal states. This is achieved by designing state-insensitive Rydberg interactions between the data-carrying atoms and cold auxiliary atoms. The resulting interactions give rise to an effective phonon coupling, which leads to the transfer of heat from the data atoms to the auxiliary atoms, where the latter can be cooled by conventional methods. This can be used to extend the lifetime of quantum storage based on neutral atoms and can have applications for long quantum computations. The protocol can also be modified to realize state-insensitive interactions between the data and the auxiliary atoms but tunable and nontrivial interactions among the data atoms, allowing one to simultaneously cool and simulate a quantum spin model.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.123.213603}, author = {Belyansky, Ron and Young, Jeremy T. and Bienias, Przemyslaw and Eldredge, Zachary and Kaufman, Adam M. and Zoller, Peter and Gorshkov, V, Alexey} } @article {ISI:000469324000004, title = {Nonlinear waves in an experimentally motivated ring-shaped Bose-Einstein-condensate setup}, journal = {Phys. Rev. A}, volume = {99}, number = {5}, year = {2019}, month = {MAY 29}, pages = {053619}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We systematically construct stationary soliton states in a one-component, two-dimensional, repulsive, Gross-Pitaevskii equation with a ring-shaped targetlike trap similar to the potential used to confine a Bose-Einstein condensate in a recent experiment {[}R. Mathew, A. Kumar, S. Eckel, F. Jendrzejewski, G. K. Campbell, M. Edwards, and E. Tiesinga, Phys. Rev. A 92, 033602 (2015)]. In addition to the ground-state configuration, we identify a wide variety of excited states involving phase jumps (and associated dark solitons) inside the ring. These configurations are obtained from a systematic bifurcation analysis starting from the linear, small atom density, limit. We study the stability and, when unstable, the dynamics of the most basic configurations. Often these lead to vortical dynamics inside the ring persisting over long time scales in our numerical experiments. To illustrate the relevance of the identified states, we showcase how such dark-soliton configurations (even the unstable ones) can be created in laboratory condensates by using phase-imprinting techniques.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.99.053619}, author = {Haberichter, M. and Kevrekidis, P. G. and Carretero-Gonzalez, R. and Edwards, M.} } @article {ISI:000455320600043, title = {Observation of chiral zero mode in inhomogeneous three-dimensional Weyl metamaterials}, journal = {Science}, volume = {363}, number = {6423}, year = {2019}, month = {JAN 11}, pages = {148-151}, publisher = {AMER ASSOC ADVANCEMENT SCIENCE}, type = {Article}, abstract = {Owing to the chirality of Weyl nodes, the Weyl systems can support one-way chiral zero modes under a strong magnetic field, which leads to nonconservation of chiral currents-the so-called chiral anomaly. Although promising for robust transport of optical information, the zero chiral bulk modes have not been observed in photonics. Here we design an inhomogeneous Weyl metamaterial in which a gauge field is generated for the Weyl nodes by engineering the individual unit cells. We experimentally confirm the presence of the gauge field and observe the zero-order chiral Landau level with one-way propagation. Without breaking the time-reversal symmetry, our system provides a route for designing an artificial magnetic field in three-dimensional photonic Weyl systems and may have potential for device applications in photonics.}, issn = {0036-8075}, doi = {10.1126/science.aau7707}, author = {Jia, Hongwei and Zhang, Ruixing and Gao, Wenlong and Guo, Qinghua and Yang, Biao and Hu, Jing and Bi, Yangang and Xiang, Yuanjiang and Liu, Chaoxing and Zhang, Shuang} } @article {ISI:000467042000002, title = {Observation of Many-Body Localization in a One-Dimensional System with a Single-Particle Mobility Edge}, journal = {Phys. Rev. Lett.}, volume = {122}, number = {17}, year = {2019}, month = {MAY 3}, pages = {170403}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We experimentally study many-body localization (MBL) with ultracold atoms in a weak onedimensional quasiperiodic potential, which in the noninteracting limit exhibits an intermediate phase that is characterized by a mobility edge. We measure the time evolution of an initial charge density wave after a quench and analyze the corresponding relaxation exponents. We find clear signatures of MBL when the corresponding noninteracting model is deep in the localized phase. We also critically compare and contrast our results with those from a tight-binding Aubry-Andre model, which does not exhibit a singleparticle intermediate phase, in order to identify signatures of a potential many-body intermediate phase.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.122.170403}, author = {Kohlert, Thomas and Scherg, Sebastian and Li, Xiao and Lueschen, Henrik P. and S. Das Sarma and Bloch, Immanuel and Aidelsburger, Monika} } @article {ISI:000461126600036, title = {Optical clock comparison for Lorentz symmetry testing}, journal = {Nature}, volume = {567}, number = {7747}, year = {2019}, month = {MAR 14}, pages = {204+}, publisher = {NATURE PUBLISHING GROUP}, type = {Article}, abstract = {Questioning basic assumptions about the structure of space and time has greatly enhanced our understanding of nature. State-of-the-art atomic clocks(1-3) make it possible to precisely test fundamental symmetry properties of spacetime and search for physics beyond the standard model at low energies of just a few electronvolts(4). Modern tests of Einstein{\textquoteright}s theory of relativity try to measure so-far-undetected violations of Lorentz symmetry(5); accurately comparing the frequencies of optical clocks is a promising route to further improving such tests(6). Here we experimentally demonstrate agreement between two single-ion optical clocks at the 10(-18) level, directly validating their uncertainty budgets, over a six-month comparison period. The ytterbium ions of the two clocks are confined in separate ion traps with quantization axes aligned along non-parallel directions. Hypothetical Lorentz symmetry violations(5-7) would lead to periodic modulations of the frequency offset as the Earth rotates and orbits the Sun. From the absence of such modulations at the 10(-19) level we deduce stringent limits of the order of 10(-21) on Lorentz symmetry violation parameters for electrons, improving previous limits(8-10) by two orders of magnitude. Such levels of precision will be essential for low-energy tests of future quantum gravity theories describing dynamics at the Planck scale(4), which are expected to predict the magnitude of residual symmetry violations.}, issn = {0028-0836}, doi = {10.1038/s41586-019-0972-2}, author = {Sanner, Christian and Huntemann, Nils and Lange, Richard and Tamm, Christian and Peik, Ekkehard and Safronova, Marianna S. and Porsev, Sergey G.} } @article {ISI:000462898900011, title = {Optical response of Luttinger semimetals in the normal and superconducting states}, journal = {Phys. Rev. B}, volume = {99}, number = {12}, year = {2019}, month = {MAR 25}, pages = {125146}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We investigate the optical response properties of three-dimensional Luttinger semimetals with the Fermi energy close to a quadratic band touching point. In particular, in order to address recent experiments on the spectroscopy of pyrochlore iridates and half-Heusler superconductors, we derive expressions for the optical conductivity in both the normal and general superconducting states in the linear response regime within the random phase approximation. The response functions can be decomposed into contributions from intraband and interband transitions, the latter comprising a genuine signature of the quadratic band touching point. We demonstrate the importance of interband transitions in the optical response in the normal state both in the homogeneous and quasistatic limit. Our analysis reveals a factorization property of the homogeneous conductivity in the spatially anisotropic case and the divergence of the conductivity for strong spatial anisotropy. In the quasistatic limit, the response is dominated by interband transitions and significantly different from systems with a single parabolic band. As an applications of the formalism in the superconducting state we compute the optical conductivity and superfluid density for the s-wave singlet superconducting case for both finite and vanishing chemical potential.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.125146}, author = {Boettcher, Igor} } @article {ISI:000473132200039, title = {Orbital-flop Induced Magnetoresistance Anisotropy in Rare Earth Monopnictide CeSb}, journal = {Nat. Commun.}, volume = {10}, year = {2019}, month = {JUN 28}, pages = {2875}, publisher = {NATURE PUBLISHING GROUP}, type = {Article}, abstract = {The charge and spin of the electrons in solids have been extensively exploited in electronic devices and in the development of spintronics. Another attribute of electrons-their orbital nature-is attracting growing interest for understanding exotic phenomena and in creating the next-generation of quantum devices such as orbital qubits. Here, we report on orbital-flop induced magnetoresistance anisotropy in CeSb. In the low temperature high magnetic-field driven ferromagnetic state, a series of additional minima appear in the angle-dependent magnetoresistance. These minima arise from the anisotropic magnetization originating from orbital-flops and from the enhanced electron scattering from magnetic multidomains formed around the first-order orbital-flop transition. The measured magnetization anisotropy can be accounted for with a phenomenological model involving orbital-flops and a spin-valve-like structure is used to demonstrate the viable utilization of orbital-flop phenomenon. Our results showcase a contribution of orbital behavior in the emergence of intriguing phenomena.}, issn = {2041-1723}, doi = {10.1038/s41467-019-10624-z}, author = {Xu, Jing and Wu, Fengcheng and Bao, Jin-Ke and Han, Fei and Xiao, Zhi-Li and Martin, Ivar and Lyu, Yang-Yang and Wang, Yong-Lei and Chung, Duck Young and Li, Mingda and Zhang, Wei and Pearson, John E. and Jiang, Jidong S. and Kanatzidis, Mercouri G. and Kwok, Wai-Kwong} } @article {ISI:000456825600004, title = {Origin of spectral brightness variations in InAs/InP quantum dot telecom single photon emitters}, journal = {J. Vac. Sci. Technol. B}, volume = {37}, number = {1}, year = {2019}, month = {JAN}, pages = {011202}, publisher = {A V S AMER INST PHYSICS}, type = {Article}, abstract = {Long-distance quantum communication relies on the ability to efficiently generate and prepare single photons at telecom wavelengths. Low-density InAs quantum dots on InP surfaces are grown in a molecular beam epitaxy system using a modified Stranski-Krastanov growth paradigm. This material is a source of bright and indistinguishable single photons in the 1.3 mu m telecom band. Here, the exploration of the growth parameters is presented as a phase diagram, while low-temperature photoluminescence and atomic resolution images are presented to correlate structure and spectral performance. This work identifies specific stacking faults and V-shaped defects that are likely causes of the observed low brightness emission at 1.55 mu m telecom wavelengths. The different locations of the imaged defects suggest possible guidance for future development of InAs/InP single photon sources for c-band, 1.55 mu m wavelength telecommunication systems.}, issn = {1071-1023}, doi = {10.1116/1.5042540}, author = {Richardson, Christopher J. K. and Leavitt, Richard P. and Kim, Je-Hyung and Waks, Edo and Arslan, Ilke and Arey, Bruce} } @article {14571, title = {Parallel entangling operations on a universal ion-trap quantum computer}, journal = {Nature}, year = {2019}, doi = {10.1038/s41586-019-1427-5}, url = {https://www.nature.com/articles/s41586-019-1427-5}, author = {Figgatt, Caroline and Ostrander, A and Linke, Norbert M. and Landsman, Kevin A. and Zhu, D and Maslov, Dmitri and Christopher Monroe} } @article {14286, title = {Parametric Heating in a 2D Periodically Driven Bosonic System: Beyond the Weakly Interacting Regime}, journal = {Physical Review X}, volume = {9}, year = {2019}, pages = {011047}, author = {Boulier, T and Maslek, J and Bukov, M and Bracamontes, C and Magnan, E and Lellouch, S and Demler, E and Goldman, N and Porto, J V} } @article {ISI:000461066200001, title = {Parametric Heating in a 2D Periodically Driven Bosonic System: Beyond the Weakly Interacting Regime}, journal = {Phys. Rev. X}, volume = {9}, number = {1}, year = {2019}, month = {MAR 13}, pages = {011047}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We experimentally investigate the effects of parametric instabilities on the short-time heating process of periodically driven bosons in 2D optical lattices with a continuous transverse (tube) degree of freedom. We analyze three types of periodic drives: (i) linear along the x-lattice direction only, (ii) linear along the lattice diagonal, and (iii) circular in the lattice plane. In all cases, we demonstrate that the Bose-Einstein condensate (BEC) decay is dominated by the emergence of unstable Bogoliubov modes, rather than scattering in higher Floquet bands, in agreement with recent theoretical predictions. The observed BEC depletion rates are much higher when shaking along both the x and y directions, as opposed to only x or only y. We also report an explosion of the decay rates at large drive amplitudes and suggest a phenomenological description beyond the Bogoliubov theory. In this strongly coupled regime, circular drives heat faster than diagonal drives, which illustrates the nontrivial dependence of the heating on the choice of drive.}, issn = {2160-3308}, doi = {10.1103/PhysRevX.9.011047}, author = {Boulier, T. and Maslek, J. and Bukov, M. and Bracamontes, C. and Magnan, E. and Lellouch, S. and Demler, E. and Goldman, N. and Porto, V, J.} } @article {ISI:000473018000001, title = {Parton construction of particle-hole-conjugate Read-Rezayi parafermion fractional quantum Hall states and beyond}, journal = {Phys. Rev. B}, volume = {99}, number = {24}, year = {2019}, month = {JUN 19}, pages = {241108}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The Read-Rezayi (RR) parafermion states form a series of exotic non-Abelian fractional quantum Hall (FQH) states at filling. = k/(k + 2). Computationally, the wave functions of these states are prohibitively expensive to generate for large systems. We introduce a series of parton states, denoted (\$2) over bar (k)1(k+1), and show that they lie in the same universality classes as the particle-hole-conjugate RR ({{\textquoteright}{\textquoteright}}anti-RR{{\textquoteright}{\textquoteright}}) states. Our analytical results imply that a {[}U(1)(k+1) xU(2k)(-1)]/{[}SU(k)(-2) xU(1)(-1)] coset conformal field theory describes the edge excitations of the (2) over bar (k)1(k+1) state, suggesting nontrivial dualities with respect to previously known descriptions. The parton construction allows wave functions in anti-RR phases to be generated for hundreds of particles. We further propose the parton sequence (n) over bar(2) over bar (4), with n = 1, 2, 3, to describe the FQH states observed at nu= 2 + 1/2, 2 + 2/5, and 2 + 3/8.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.241108}, author = {Balram, Ajit C. and Barkeshli, Maissam and Rudner, Mark S.} } @article {14481, title = {Perfect Andreev reflection due to the Klein paradox in a topological superconducting state}, journal = {Nature}, volume = {570}, year = {2019}, pages = {344{\textendash}348}, abstract = {In 1928, Dirac proposed a wave equation to describe relativistic electrons1. Shortly afterwards, Klein solved a simple potential step problem for the Dirac equation and encountered an apparent paradox: the potential barrier becomes transparent when its height is larger than the electron energy. For massless particles, backscattering is completely forbidden in Klein tunnelling, leading to perfect transmission through any potential barrier2,3. The recent advent of condensed-matter systems with Dirac-like excitations, such as graphene and topological insulators, has opened up the possibility of observing Klein tunnelling experimentally4{\textendash}6. In the surface states of topological insulators, fermions are bound by spin{\textendash}momentum locking and are thus immune from backscattering, which is prohibited by time-reversal symmetry. Here we report the observation of perfect Andreev reflection in point-contact spectroscopy{\textendash}-a clear signature of Klein tunnelling and a manifestation of the underlying {\textquoteleft}relativistic{\textquoteright}physics of a proximity-induced superconducting state in a topological Kondo insulator. Our findings shed light on a previously overlooked aspect of topological superconductivity and can serve as the basis for a unique family of spintronic and superconducting devices, the interface transport phenomena of which are completely governed by their helical topological states.

}, isbn = {1476-4687}, doi = {10.1038/s41586-019-1305-1}, url = {https://doi.org/10.1038/s41586-019-1305-1}, author = {Lee, Seunghun and Stanev, Valentin and Zhang, Xiaohang and Stasak, Drew and Flowers, Jack and Higgins, Joshua S. and Dai, Sheng and Blum, Thomas and Pan, Xiaoqing and Yakovenko, Victor M. and Paglione, Johnpierre and Greene, Richard L. and Galitski, Victor and Takeuchi, Ichiro} } @article {ISI:000463889200003, title = {Phonon-induced giant linear-in-T resistivity in magic angle twisted bilayer graphene: Ordinary strangeness and exotic superconductivity}, journal = {Phys. Rev. B}, volume = {99}, number = {16}, year = {2019}, month = {APR 9}, pages = {165112}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study the effect of electron-acoustic phonon interactions in twisted bilayer graphene on resistivity in the high-temperature transport and superconductivity in the low-temperature phase diagram. We theoretically show that twisted bilayer graphene should have an enhanced and strongly twist-angle dependent linear-in-temperature resistivity in the metallic regime with the resistivity magnitude increasing as the twist angle approaches the magic angle. The slope of the resistivity versus temperature could approach one hundred ohm per kelvin with a strong angle dependence, but with a rather weak dependence on the carrier density. This higher-temperature density-independent linear-in-T resistivity crosses over to a T-4 dependence at a low density-dependent characteristic temperature, becoming unimportant at low temperatures. This angle-tuned resistivity enhancement arises from the huge increase in the effective electron-acoustic phonon coupling in the system due to the suppression of graphene Fermi velocity induced by the flat-band condition in the moire superlattice system. Our calculated temperature dependence is reminiscent of the so-called {\textquoteleft}{\textquoteleft}strange metal{{\textquoteright}{\textquoteright}} transport behavior except that it is arising from the ordinary electron-phonon coupling in a rather unusual parameter space due to the generic moire flat-band structure of twisted bilayer graphene. We also show that the same enhanced electron-acoustic phonon coupling also mediates effective attractive interactions in s, p, d, and f pairing channels with a theoretical superconducting transition temperature on the order of similar to 5 K near magic angle. The fact that ordinary acoustic phonons can produce exotic non-s-wave superconducting pairing arises from the unusual symmetries of the system.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.165112}, author = {Wu, Fengcheng and Hwang, Euyheon and S. Das Sarma} } @article {21371, title = {Phonon-induced giant linear-in-T resistivity in magic angle twisted bilayer graphene: Ordinary strangeness and exotic superconductivity}, journal = {Phys. Rev. B}, volume = {99}, year = {2019}, month = {Apr}, pages = {165112}, abstract = {We study the effect of electron-acoustic phonon interactions in twisted bilayer graphene on resistivity in the high-temperature transport and superconductivity in the low-temperature phase diagram. We theoretically show that twisted bilayer graphene should have an enhanced and strongly twist-angle dependent linear-in-temperature resistivity in the metallic regime with the resistivity magnitude increasing as the twist angle approaches the magic angle. The slope of the resistivity versus temperature could approach one hundred ohm per kelvin with a strong angle dependence, but with a rather weak dependence on the carrier density. This higher-temperature density-independent linear-in-T\ resistivity crosses over to a\ T4\ dependence at a low density-dependent characteristic temperature, becoming unimportant at low temperatures. This angle-tuned resistivity enhancement arises from the huge increase in the effective electron-acoustic phonon coupling in the system due to the suppression of graphene Fermi velocity induced by the flat-band condition in the moir{\'e} superlattice system. Our calculated temperature dependence is reminiscent of the so-called {\textquotedblleft}strange metal{\textquotedblright} transport behavior except that it is arising from the ordinary electron-phonon coupling in a rather unusual parameter space due to the generic moir{\'e} flat-band structure of twisted bilayer graphene. We also show that the same enhanced electron-acoustic phonon coupling also mediates effective attractive interactions in\ s,p,d, and\ f\ pairing channels with a theoretical superconducting transition temperature on the order of\ \~{}5\ K near magic angle. The fact that ordinary acoustic phonons can produce exotic non-s-wave superconducting pairing arises from the unusual symmetries of the system.

}, doi = {10.1103/PhysRevB.99.165112}, url = {https://link.aps.org/doi/10.1103/PhysRevB.99.165112}, author = {Wu, Fengcheng and Hwang, Euyheon and Das Sarma, Sankar} } @article {ISI:000479005400008, title = {Photon Pair Condensation by Engineered Dissipation}, journal = {Phys. Rev. Lett.}, volume = {123}, number = {6}, year = {2019}, month = {AUG 6}, pages = {063602}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Dissipation can usually induce detrimental decoherence in a quantum system. However, engineered dissipation can be used to prepare and stabilize coherent quantum many-body states. Here, we show that, by engineering dissipators containing photon pair operators, one can stabilize an exotic dark state, which is a condensate of photon pairs with a phase-nematic order. In this system, the usual superfluid order parameter, i.e., single-photon correlation, is absent, while the photon pair correlation exhibits long-range order. Although the dark state is not unique due to multiple parity sectors, we devise an additional type of dissipators to stabilize the dark state in a particular parity sector via a diffusive annihilation process which obeys Glauber dynamics in an Ising model. Furthermore, we propose an implementation of these photon pair dissipators in circuit-QED architecture.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.123.063602}, author = {Cian, Ze-Pei and Zhu, Guanyu and Chu, Su-Kuan and Seif, Alireza and DeGottardi, Wade and Jiang, Liang and Hafezi, Mohammad} } @article {ISI:000477918500001, title = {Photonic Anomalous Quantum Hall Effect}, journal = {Phys. Rev. Lett.}, volume = {123}, number = {4}, year = {2019}, month = {JUL 23}, pages = {043201}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We experimentally realize a photonic analogue of the anomalous quantum Hall insulator using a two-dimensional (2D) array of coupled ring resonators. Similar to the Haldane model, our 2D array is translation invariant, has a zero net gauge flux threading the lattice, and exploits next-nearest neighbor couplings to achieve a topologically nontrivial band gap. Using direct imaging and on-chip transmission measurements, we show that the band gap hosts topologically robust edge states. We demonstrate a topological phase transition to a conventional insulator by frequency detuning the ring resonators and thereby breaking the inversion symmetry of the lattice. Furthermore, the clockwise or the counterclockwise circulation of photons in the ring resonators constitutes a pseudospin degree of freedom. The two pseudospins acquire opposite hopping phases, and their respective edge states propagate in opposite directions. These results are promising for the development of robust reconfigurable integrated nanophotonic devices for applications in classical and quantum information processing.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.123.043201}, author = {Mittal, Sunil and Orre, Venkata Vikram and Leykam, Daniel and Chong, Y. D. and Hafezi, Mohammad} } @article {14466, title = {Photonic quadrupole topological phases}, journal = {Nature Photonics}, year = {2019}, abstract = {The topological phases of matter are characterized using the Berry phase, a geometrical phase associated with the energy-momentum band structure. The quantization of the Berry phase and the associated wavefunction polarization manifest as remarkably robust physical observables, such as quantized Hall conductivity and disorder-insensitive photonic transport1{\textendash}5. Recently, a novel class of topological phases, called higher-order topological phases, were proposed by generalizing the fundamental relationship between the Berry phase and quantized polarization, from dipole to multipole moments6{\textendash}8. Here, we demonstrate photonic realization of the quantized quadrupole topological phase, using silicon photonics. In our two-dimensional second-order topological phase, we show that the quantization of the bulk quadrupole moment manifests as topologically robust zero-dimensional corner states. We contrast these topological states against topologically trivial corner states in a system without bulk quadrupole moment, where we observe no robustness. Our photonic platform could enable the development of robust on-chip classical and quantum optical devices with higher-order topological protection.

}, isbn = {1749-4893}, doi = {10.1038/s41566-019-0452-0}, url = {https://doi.org/10.1038/s41566-019-0452-0}, author = {Mittal, Sunil and Orre, Venkata Vikram and Zhu, Guanyu and Gorlach, Maxim A. and Poddubny, Alexander and Hafezi, Mohammad} } @article { ISI:000492332900006, title = {Polarizability assessments of ion-based optical clocks}, journal = {Phys. Rev. A}, volume = {100}, number = {4}, year = {2019}, month = {OCT 24}, pages = {043418}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {It is shown that the dynamic differential scalar polarizability of the S-1/2 - D-5/2 transition in Ba-138(+) can be determined to an inaccuracy below 0.5\% across a wide wavelength range (lambda > 700 nm). This can be achieved using measurements for which accurate determination of laser intensity is not required, and most of the required measurements are already in the literature. Measurement of a laser-induced ac-Stark shift of the clock transition would then provide an in situ measurement of the laser{\textquoteright}s intensity to the same 0.5\% level of inaccuracy, which is not easily achieved by other means. This would allow accurate polarizability measurements for clock transitions in other ions, through comparison with Ba-138(+). The approach would be equally applicable to Sr+ and Ca+, with the latter being immediately applicable to Al+/Ca+ quantum logic clocks.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.100.043418}, author = {Barrett, M. D. and Arnold, K. J. and Safronova, M. S.} } @article { ISI:000488249400003, title = {Polynomial time algorithms for estimating spectra of adiabatic Hamiltonians}, journal = {Phys. Rev. A}, volume = {100}, number = {3}, year = {2019}, month = {SEP 30}, pages = {032336}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Much research regarding quantum adiabatic optimization has focused on stoquastic Hamiltonians with Hamming-symmetric potentials, such as the well-studied {\textquoteleft}{\textquoteleft}spike{{\textquoteright}{\textquoteright}} example. Due to the large amount of symmetry in these potentials such problems are readily open to analysis both analytically and computationally. However, more realistic potentials do not have such a high degree of symmetry and may have many local minima Here we present a somewhat more realistic class of problems consisting of many individually Hamming-symmetric potential wells. For two or three such wells we demonstrate that such a problem can be solved exactly in time polynomial in the number of qubits and wells. For greater than three wells, we present a tight-binding approach with which to efficiently analyze the performance of such Hamiltonians in an adiabatic computation. We provide several basic examples designed to highlight the usefulness of this toy model and to give insight into using the tight-binding approach to examining it, including (1) an adiabatic unstructured search with a transverse field driver and a prior guess to the marked item and (2) a scheme for adiabatically simulating the ground states of small collections of strongly interacting spins, with an explicit demonstration for an Ising-model Hamiltonian.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.100.032336}, author = {Bringewatt, Jacob and Dorland, William and Jordan, Stephen P.} } @article {ISI:000454776000002, title = {Possible Hundredfold Enhancement in the Direct Magnetic Coupling of a Single-Atom Electron Spin to a Circuit Resonator}, journal = {Phys. Rev. Appl.}, volume = {11}, number = {1}, year = {2019}, month = {JAN 2}, pages = {014001}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We report on the challenges and limitations of direct coupling of the magnetic field from a circuit resonator to an electron spin bound to a donor potential. We propose a device consisting of a trilayer lumped-element superconducting resonator and a single donor implanted in enriched Si-28. The resonator impedance is significantly smaller than the practically achievable limit obtained with prevalent coplanar resonators. Furthermore, the resonator includes a nanoscale spiral inductor to spatially focus the magnetic field from the photons at the location of the implanted donor. The design promises an increase of approximately 2 orders of magnitude in the local magnetic field, and thus the spin-to-photon coupling rate g, compared with the estimated rate of coupling to the magnetic field of coplanar transmission line resonators. We show that by use of niobium (aluminum) as the resonator{\textquoteright}s superconductor and a single phosphorous (bismuth) atom as the donor, a coupling rate of g/2 pi = 0.24 MHz (0.39 MHz) can be achieved in the single-photon regime. For this hybrid cavity-quantum-electrodynamic system, such enhancement in g is sufficient to enter the strong-coupling regime.}, issn = {2331-7019}, doi = {10.1103/PhysRevApplied.11.014001}, author = {Sarabi, Bahman and Huang, Peihao and Zimmerman, Neil M.} } @conference {ISI:000481657400006, title = {A post-processing-free single-photon random number generator with ultra-low latency}, booktitle = {ADVANCES IN PHOTONICS OF QUANTUM COMPUTING, MEMORY, AND COMMUNICATION XII}, series = {Proceedings of SPIE}, volume = {10933}, year = {2019}, note = {Conference on Advances in Photonics of Quantum Computing, Memory, and Communication XII, San Francisco, CA, FEB 05-07, 2019}, pages = {109330F}, publisher = {SPIE}, organization = {SPIE}, type = {Proceedings Paper}, abstract = {The low-latency requirements of a loophole-free Bell test prohibit time-consuming post-processing steps that arc often used to improve the statistical quality of a physical random number generator (RNG). Here we demonstrate a post-processing-free RNG that produces a random bit within 2.4(2) ns of an input trigger. We use the Allan variance as a tool for characterizing non-idealities in the RNG and designing a feedback mechanism to account for and correct long-term drift. The impact of the feedback on the predictability of the output is less than 6.4 x 10(7), and results in a system capable of 24 hour operation with output that is statistically indistinguishable from a balanced Bernoulli process.}, keywords = {Bell test, low latency, Quantum Information, random number generator, single-photon}, isbn = {978-1-5106-2509-9}, issn = {0277-786X}, doi = {10.1117/12.2514855}, author = {Wayne, Michael A. and Migdall, Alan L. and Levine, Zachary H. and Bienfang, Joshua C.}, editor = {Hemmer, PR and Migdall, AL and UlHasan, Z} } @article { ISI:000499991300005, title = {Precision Test of the Limits to Universality in Few-Body Physics}, journal = {Phys. Rev. Lett.}, volume = {123}, number = {23}, year = {2019}, month = {DEC 2}, pages = {233402}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We perform precise studies of two- and three-body interactions near an intermediate-strength Feshbach resonance in K-39 at 33.5820(14) G. Precise measurement of dimer binding energies, spanning three orders of magnitude, enables the construction of a complete two-body coupled-channel model for determination of the scattering lengths with an unprecedented low uncertainty. Utilizing an accurate scattering length map, we measure the precise location of the Efimov ground state to test van der Waals universality. Precise control of the sample{\textquoteright}s temperature and density ensures that systematic effects on the Efimov trimer state are well understood. We measure the ground Efimov resonance location to be at -14.05(17) times the van der Waals length r(vdW), significantly deviating from the value of -9.7r(vdW) predicted by van der Waals universality. We find that a refined multichannel three-body model, built on our measurement of two-body physics, can account for this difference and even successfully predict the Efimov inelasticity parameter eta.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.123.233402}, author = {Chapurin, Roman and Xie, Xin and Van de Graaff, Michael J. and Popowski, Jared S. and D{\textquoteright}Incao, Jose P. and Julienne, Paul S. and Ye, Jun and Cornell, Eric A.} } @article {ISI:000473540500004, title = {Prediction of a Non-Abelian Fractional Quantum Hall State with f-Wave Pairing of Composite Fermions in Wide Quantum Wells}, journal = {Phys. Rev. Lett.}, volume = {123}, number = {1}, year = {2019}, month = {JUL 2}, pages = {016802}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We theoretically investigate the nature of the state at the quarter filled lowest Landau level and predict that, as the quantum well width is increased, a transition occurs from the composite fermion Fermi sea into a novel non-Abelian fractional quantum Hall state that is topologically equivalent to f-wave pairing of composite fermions. This state is topologically distinct from the familiar p-wave paired Pfaffian state. We compare our calculated phase diagram with experiments and make predictions for many observable quantities.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.123.016802}, author = {Faugno, W. N. and Balram, Ajit C. and Barkeshli, Maissam and Jain, J. K.} } @article {ISI:000474369000008, title = {Presence versus absence of end-to-end nonlocal conductance correlations in Majorana nanowires: Majorana bound states versus Andreev bound states}, journal = {Phys. Rev. B}, volume = {100}, number = {4}, year = {2019}, month = {JUL 3}, pages = {045302}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {By calculating the differential tunneling conductance spectra from the two ends of a Majorana nanowire with a quantum dot embedded at one end, we establish that a careful examination of the nonlocal correlations of the zero-bias conductance peaks, as measured separately from the two ends of the wire, can distinguish between topological Majorana bound states and trivial Andreev bound states. In particular, there will be identical correlated zero-bias peaks from both ends for Majorana bound states, and thus the presence of correlated zero-bias conductance from the two wire ends could imply the presence of topological Majorana zero modes in the system. On the contrary, there will not be identical correlated zero-bias peaks from both ends for Andreev bound states, so the absence of correlated zero-bias conductance from the two wire ends implies the absence of topological Majorana zero modes in the system. We present detailed results for the calculated conductance, energy spectra, and wave functions for different chemical potentials at the same magnetic field values to motivate end-to-end conductance correlation measurements in Majorana nanowires.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.100.045302}, author = {Lai, Yi-Hua and Sau, Jay D. and S. Das Sarma} } @article {ISI:000485202800004, title = {Probing Ground-State Phase Transitions through Quench Dynamics}, journal = {Phys. Rev. Lett.}, volume = {123}, number = {11}, year = {2019}, month = {SEP 11}, pages = {115701}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The study of quantum phase transitions requires the preparation of a many-body system near its ground state, a challenging task for many experimental systems. The measurement of quench dynamics, on the other hand, is now a routine practice in most cold atom platforms. Here we show that quintessential ingredients of quantum phase transitions can be probed directly with quench dynamics in integrable and nearly integrable systems. As a paradigmatic example, we study global quench dynamics in a transverse-field Ising model with either short-range or long-range interactions. When the model is integrable, we discover a new dynamical critical point with a nonanalytic signature in the short-range correlators. The location of the dynamical critical point matches that of the quantum critical point and can be identified using a finite-time scaling method. We extend this scaling picture to systems near integrability and demonstrate the continued existence of a dynamical critical point detectable at prethermal timescales. We quantify the difference in the locations of the dynamical and quantum critical points away from (but near) integrability. Thus, we demonstrate that this method can be used to approximately locate the quantum critical point near integrability. The scaling method is also relevant to experiments with finite time and system size, and our predictions are testable in near-term experiments with trapped ions and Rydberg atoms.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.123.115701}, author = {Titum, Paraj and Iosue, Joseph T. and Garrison, James R. and Gorshkov, Alexey V. and Gong, Zhe-Xuan} } @article { ISI:000499482200011, title = {Probing Trions at Chemically Tailored Trapping Defects}, journal = {ACS Central Sci.}, volume = {5}, number = {11}, year = {2019}, month = {NOV 27}, pages = {1786-1794}, publisher = {AMER CHEMICAL SOC}, type = {Article}, abstract = {Trions, charged excitons that are reminiscent of hydrogen and positronium ions, have been intensively studied for energy harvesting, light-emitting diodes, lasing, and quantum computing applications because of their inherent connection with electron spin and dark excitons. However, these quasi-particles are typically present as a minority species at room temperature making it difficult for quantitative experimental measurements. Here, we show that by chemically engineering the well depth of sp(3) quantum defects through a series of alkyl functional groups covalently attached to semiconducting carbon nanotube hosts, trions can be efficiently generated and localized at the trapping chemical defects. The exciton-electron binding energy of the trapped trion approaches 119 meV, which more than doubles that of {\textquoteleft}{\textquoteleft}free{{\textquoteright}{\textquoteright}} trions in the same host material (54 meV) and other nanoscale systems (2-45 meV). Magnetoluminescence spectroscopy suggests the absence of dark states in the energetic vicinity of trapped trions. Unexpectedly, the trapped trions are approximately 7.3-fold brighter than the brightest previously reported and 16 times as bright as native nanotube excitons, with a photoluminescence lifetime that is more than 100 times larger than that of free trions. These intriguing observations are understood by an efficient conversion of dark excitons to bright trions at the defect sites. This work makes trions synthetically accessible and uncovers the rich photophysics of these tricarrier quasi-particles, which may find broad implications in bioimaging, chemical sensing, energy harvesting, and light emitting in the short-wave infrared.}, issn = {2374-7943}, doi = {10.1021/acscentsci.9b00707}, author = {Kwon, Hyejin and Kim, Mijin and Nutz, Manuel and Hartmann, Nicolai F. and Perrin, Vivien and Meany, Brendan and Hofmann, Matthias S. and Clark, Charles W. and Htoon, Han and Doorn, Stephen K. and Hoegele, Alexander and Wang, YuHuang} } @article {ISI:000462932400012, title = {Proposal for Measuring the Parity Anomaly in a Topological Superconductor Ring}, journal = {Phys. Rev. Lett.}, volume = {122}, number = {11}, year = {2019}, month = {MAR 22}, pages = {117001}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {A topological superconductor ring is uniquely characterized by a switch in the ground state fermion number parity upon insertion of one superconducting flux quantum-a direct consequence of the topological {\textquoteleft}{\textquoteleft}parity anomaly.{{\textquoteright}{\textquoteright}} Despite the many other tantalizing signatures and applications of topological superconductors, this fundamental, defining property remains to be observed experimentally. Here we propose definitive detection of the fermion parity switch from the charging energy, temperature, and tunnel barrier dependence of the flux periodicity of two-terminal conductance of a floating superconductor ring. We extend the Ambegaokar-Eckern-Schon formalism for superconductors with a Coulomb charging energy to establish new explicit relationships between thermodynamic and transport properties of such a ring and the topological invariant of the superconductor. Crucially, we show that the topological contribution to the conductance oscillations can be isolated from Aharonov-Bohm oscillations of nontopological origin by their different dependence on the charging energy or barrier transparency.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.122.117001}, author = {Liu, Chun-Xiao and Cole, William S. and Sau, Jay D.} } @article { ISI:000496588600002, title = {Protocol for Reading Out Majorana Vortex Qubits and Testing Non-Abelian Statistics}, journal = {Phys. Rev. Appl.}, volume = {12}, number = {5}, year = {2019}, month = {NOV 14}, pages = {054035}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The successful testing of non-Abelian statistics not only serves as a milestone in fundamental physics but also provides a quantum-gate operation in topological quantum computation. An accurate and efficient readout scheme of a topological qubit is an essential step toward the experimental confirmation of non-Abelian statistics. In the current work, we propose a protocol to read out the quantum state of a Majorana vortex qubit on a topological superconductor island. The protocol consists of four Majorana zero modes trapped in spatially well-separated vortex cores on the two-dimensional surface of a Coulomb blockaded topological superconductor. Our proposed measurement is implemented by a pair of weakly coupled Majorana modes separately in touch with two normal-metal leads and the readout is realized by observing the conductance-peak location in terms of the gate voltage. Using this protocol, we can further test the non-Abelian statistics of Majorana zero modes in the two-dimensional platform. A successful readout of a Majorana qubit is a crucial step toward the future application of topological quantum computation. In addition, this Coulomb-blockaded setup can distinguish Majorana zero modes from Caroli-de Gennes-Matricon modes in vortex cores.}, issn = {2331-7019}, doi = {10.1103/PhysRevApplied.12.054035}, author = {Liu, Chun-Xiao and Liu, Dong E. and Zhang, Fu-Chun and Chiu, Ching-Kai} } @article {ISI:000471060400001, title = {pyLLE: A Fast and User Friendly Lugiato-Lefever Equation Solver}, journal = {J. Res. Natl. Inst. Stand. Technol.}, volume = {124}, year = {2019}, month = {MAY 24}, pages = {012}, publisher = {NATL INST STANDARDS \& TECHNOLOGY-NIST}, type = {Article}, keywords = {Julia, micro-combs, non-linear optics, python}, issn = {2165-7254}, doi = {10.6028/jres.124.012}, author = {Moille, Gregory and Li, Qing and Lu, Xiyuan and Srinivasan, Kartik} } @article {ISI:000484374000020, title = {Quantum electrodynamics of a superconductor-insulator phase transition}, journal = {Nat. Phys.}, volume = {15}, number = {9}, year = {2019}, month = {SEP}, pages = {930+}, publisher = {NATURE PUBLISHING GROUP}, type = {Article}, abstract = {A chain of Josephson junctions represents one of the simplest many-body models undergoing a superconductor-insulator quantum phase transition(1,2). Apart from zero resistance, the superconducting state is necessarily accompanied by a sound-like mode due to collective oscillations of the phase of the complex-valued order parameter(3,4). Little is known about the fate of this mode on entering the insulating state, where the order parameter{\textquoteright}s amplitude remains non-zero, but the phase ordering is {\textquoteleft}melted{\textquoteright} by quantum fluctuations(5). Here, we show that the phase mode survives far into the insulating regime, such that megaohm-resistance chains can carry gigahertz-frequency alternating currents as nearly ideal superconductors. The insulator reveals itself through interaction-induced broadening and random frequency shifts of collective mode resonances. Our spectroscopic experiment puts forward the problem of quantum electrodynamics of a Bose glass for both theory and experiments(6-8). By pushing the chain parameters deeper into the insulating state, we achieved a wave impedance of the phase mode exceeding the predicted critical value by an order of magnitude(9-14). The effective fine structure constant of such a one-dimensional electromagnetic vacuum exceeds unity, promising transformative applications to quantum science and technology.}, issn = {1745-2473}, doi = {10.1038/s41567-019-0553-1}, author = {Kuzmin, R. and Mencia, R. and Grabon, N. and Mehta, N. and Lin, Y-H and Manucharyan, V. E.} } @article {ISI:000468373300008, title = {Quantum frequency conversion of a quantum dot single-photon source on a nanophotonic chip}, journal = {Optica}, volume = {6}, number = {5}, year = {2019}, month = {MAY 20}, pages = {563-569}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {Single self-assembled InAs/GaAs quantum dots are promising bright sources of indistinguishable photons for quantum information science. However, their distribution in emission wavelength, due to inhomogeneous broadening inherent to their growth, has limited the ability to create multiple identical sources. Quantum frequency conversion can overcome this issue, particularly if implemented using scalable chip-integrated technologies. Here, we report the first demonstration to our knowledge of quantum frequency conversion of a quantum dot single-photon source on a silicon nanophotonic chip. Single photons from a quantum dot in a micropillar cavity are shifted in wavelength with an on-chip conversion efficiency approximate to 12\%, limited by the linewidth of the quantum dot photons. The intensity auto-correlation function g((2)) (tau) for the frequency-converted light is antibunched with g((2)) (0) = 0.290 +/- 0.030, compared to the before-conversion value g((2)) (0) = 0.080 +/- 0.003. We demonstrate the suitability of our frequency-conversion interface as a resource for quantum dot sources by characterizing its effectiveness across a wide span of input wavelengths (840-980 nm) and its ability to achieve tunable wavelength shifts difficult to obtain by other approaches. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement}, issn = {2334-2536}, doi = {10.1364/OPTICA.6.000563}, author = {Singh, Anshuman and Li, Qing and Liu, Shunfa and Yu, Ying and Lu, Xiyuan and Schneider, Christian and Hoefling, Sven and Lawall, John and Verma, Varun and Mirin, Richard and Nam, Sae Woo and Liu, Jin and Srinivasan, Kartik} } @article {ISI:000485187000003, title = {Quantum information scrambling through a high-complexity operator mapping}, journal = {Phys. Rev. A}, volume = {100}, number = {3}, year = {2019}, month = {SEP 6}, pages = {032309}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Quantum information scrambling has attracted much attention amid the effort to reconcile the conflict between quantum-mechanical unitarity and the thermalization irreversibility in many-body systems. Here we propose an unconventional mechanism to generate quantum information scrambling through a high-complexity mapping from logical to physical degrees-of-freedom that hides the logical information into nonseparable many-body correlations. Corresponding to this mapping, we develop an algorithm to efficiently sample a Slater-determinant wave function and compute all physical observables in dynamics with a polynomial cost in system size. The system shows information scrambling in the quantum many-body Hilbert space characterized by the spreading of Hamming distance. At late time we find emergence of classical diffusion dynamics in this quantum many-body system. We establish that the operator mapping enabled growth in an out-of-time-order correlator exhibits exponential-scrambling behavior. The quantum information-hiding mapping approach may shed light on the understanding of fundamental connections among computational complexity, information scrambling, and quantum thermalization.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.100.032309}, author = {Li, Xiaopeng and Zhu, Guanyu and Han, Muxin and Wang, Xin} } @article {ISI:000466809600017, title = {QUANTUM INFORMATION The US National Quantum Initiative: From Act to action}, journal = {Science}, volume = {364}, number = {6439}, year = {2019}, month = {MAY 3}, pages = {440-442}, publisher = {AMER ASSOC ADVANCEMENT SCIENCE}, type = {Editorial Material}, issn = {0036-8075}, doi = {10.1126/science.aax0578}, author = {Monroe, Christopher and Raymer, Michael G. and Taylor, Jacob} } @article { ISI:000496930000002, title = {Quantum Interference between Photons from an Atomic Ensemble and a Remote Atomic Ion}, journal = {Phys. Rev. Lett.}, volume = {123}, number = {21}, year = {2019}, month = {NOV 18}, pages = {213601}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Many remote-entanglement protocols rely on the generation and interference of photons produced by nodes within a quantum network. Quantum networks based on heterogeneous nodes provide a versatile platform by utilizing the complementary strengths of the differing systems. Implementation of such networks is challenging, due to the disparate spectral and temporal characteristics of the photons generated by the different quantum systems. Here, we report on the observation of quantum interference between photons generated from a single ion and an atomic ensemble. The photons are produced on demand by each source located in separate buildings, in a manner suitable for quantum networking. Given these results, we analyze the feasibility of hybrid ion-ensemble remote entanglement generation.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.123.213601}, author = {Craddock, A. N. and Hannegan, J. and Ornelas-Huerta, D. P. and Siverns, J. D. and Hachtel, A. J. and Goldschmidt, A. and Porto, J. V. and Quraishi, Q. and Rolston, S. L.} } @article { ISI:000498849400002, title = {Quantum many-body scars from magnon condensation}, journal = {Phys. Rev. B}, volume = {100}, number = {18}, year = {2019}, month = {NOV 27}, pages = {184312}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study the eigenstate properties of a nonintegrable spin chain that was recently realized experimentally in a Rydberg-atom quantum simulator. In the experiment, long-lived coherent many-body oscillations were observed only when the system was initialized in a particular product state. This pronounced coherence has been attributed to the presence of special {\textquoteleft}{\textquoteleft}scarred{{\textquoteright}{\textquoteright}} eigenstates with nearly equally spaced energies and putative nonergodic properties despite their finite energy density. In this paper we uncover a surprising connection between these scarred eigenstates and low-lying quasiparticle excitations of the spin chain. In particular, we show that these eigenstates can be accurately captured by a set of variational states containing a macroscopic number of magnons with momentum pi. This leads to an interpretation of the scarred eigenstates as finite-energy-density condensates of weakly interacting pi magnons. One natural consequence of this interpretation is that the scarred eigenstates possess long-range connected correlations in both space and time. We verify numerically the presence of this spatiotemporal long-range order and explain how it is consistent with established no-go theorems precluding its existence in ground states and at thermal equilibrium.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.100.184312}, author = {Iadecola, Thomas and Schecter, Michael and Xu, Shenglong} } @article {ISI:000476860700002, title = {Quantum repeaters based on two species trapped ions}, journal = {New J. Phys.}, volume = {21}, year = {2019}, month = {JUL 1}, pages = {073002}, publisher = {IOP PUBLISHING LTD}, type = {Article}, abstract = {We examine the viability of quantum repeaters based on two-species trapped ion modules for long-distance quantum key distribution. Repeater nodes comprised of ion-trap modules of co-trapped ions of distinct species are considered. The species used for communication qubits has excellent optical properties while the other longer lived species serves as a memory qubit in the modules. Each module interacts with the network only via single photons emitted by the communication ions. Coherent Coulomb interaction between ions is utilized to transfer quantum information between the communication and memory ions and to achieve entanglement swapping between two memory ions. We describe simple modular quantum repeater architectures realizable with the ion-trap modules and numerically study the dependence of the quantum key distribution rate on various experimental parameters, including coupling efficiency, gate infidelity, operation time and length of the elementary links. Our analysis suggests crucial improvements necessary in a physical implementation for co-trapped two-species ions to be a competitive platform in long-distance quantum communication.}, keywords = {quantum key distribution, quantum repeaters, two species trapped ions}, issn = {1367-2630}, doi = {10.1088/1367-2630/ab2a45}, author = {Santra, Siddhartha and Muralidharan, Sreraman and Lichtman, Martin and Jiang, Liang and Monroe, Christopher and Malinovsky, Vladimir S.} } @article {ISI:000472681100001, title = {Quantum Sensing with Squeezed Light}, journal = {ACS Photonics}, volume = {6}, number = {6}, year = {2019}, month = {JUN}, pages = {1307-1318}, publisher = {AMER CHEMICAL SOC}, type = {Article}, abstract = {The minimum resolvable signal in sensing and metrology platforms that rely on optical readout fields is increasingly constrained by the standard quantum limit, which is determined by the sum of photon shot noise and back-action noise. A combination of back-action and shot noise reduction techniques will be critical to the development of the next generation of sensors for applications ranging from high-energy physics to biochemistry and for novel microscopy platforms capable of resolving material properties that were previously obscured by quantum noise. This Perspective reviews the dramatic advances made in the use of squeezed light for sub-shot-noise quantum sensing in recent years and highlights emerging applications that enable new science based on signals that would otherwise be obscured by noise at the standard quantum limit.}, keywords = {continuous variable quantum optics, quantum noise reduction, quantum sensing, squeezing}, issn = {2330-4022}, doi = {10.1021/acsphotonics.9b00250}, author = {Lawrie, B. J. and Lett, P. D. and Marino, A. M. and Pooser, R. C.} } @article {ISI:000482580900004, title = {Quantum work of an optical lattice}, journal = {Phys. Rev. B}, volume = {100}, number = {6}, year = {2019}, month = {AUG 26}, pages = {064308}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {A classic example of a quantum quench concerns the release of an interacting Bose gas from an optical lattice. The local properties of quenches such as this have been extensively studied; however, the global properties of these nonequilibrium quantum systems have received far less attention. Here we study several aspects of global nonequilibrium behavior by calculating the amount of work done by the quench as measured through the work distribution function. Using Bethe ansatz techniques, we determine the Loschmidt amplitude and work distribution function of the Lieb-Liniger gas after it is released from an optical lattice. We find the average work and its universal edge exponents from which we determine the long-time decay of the Loschmidt echo and highlight striking differences caused by the interactions as well as changes in the geometry of the system. We extend our calculation to the attractive regime of the model and show that the system exhibits properties similar to the super-Tonks-Girardeau gas. Finally, we examine the prominent role played by bound states in the work distribution and show that, with low probability, they allow for work to be extracted from the quench.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.100.064308}, author = {Rylands, Colin and Andrei, Natan} } @conference {ISI:000482226301355, title = {Quantum-correlated Light Source from Dual-seeded Four-wave Mixing with a Diode Laser System}, booktitle = {2019 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO)}, series = {Conference on Lasers and Electro-Optics}, year = {2019}, note = {Conference on Lasers and Electro-Optics (CLEO), San Jose, CA, MAY 05-10, 2019}, publisher = {IEEE; AdValue Photon; Amer Elements; Class5 Photon; Coherent; GoFoton; Light Convers; LightTrans; MKS; OZ Opt Online; Santec; ThorLabs; UQDevices; YSL Photon}, organization = {IEEE; AdValue Photon; Amer Elements; Class5 Photon; Coherent; GoFoton; Light Convers; LightTrans; MKS; OZ Opt Online; Santec; ThorLabs; UQDevices; YSL Photon}, type = {Proceedings Paper}, abstract = {We have obtained broadband intensity-difference squeezing from sub 10 Hz to 20 MHz via four-wave mixing (4WM) in a rubidium vapor. This was accomplished by dual-seeding the 4WM process and using semiconductor diode lasers. (C) 2019 The Author(s)}, isbn = {978-1-943580-57-6}, issn = {2160-9020}, author = {Wu, Meng-Chang and Brewer, Nicholas R. and Speirs, Rory W. and Schmittberger, Bonnie L. and Jones, Kevin M. and Lett, Paul D.} } @article {ISI:000470151800023, title = {Reduction of water-molecule-induced current-voltage hysteresis in graphene field effect transistor with semi-dry transfer using flexible supporter}, journal = {J. Appl. Phys.}, volume = {125}, number = {18}, year = {2019}, month = {MAY 14}, pages = {184302}, publisher = {AMER INST PHYSICS}, type = {Article}, abstract = {The polymethyl methacrylate-assisted wet transfer method of chemical vapor deposition (CVD) graphene has been widely used, thanks to its good coverage and simplicity. However, in the wet-transfer method, water molecules are inevitably trapped between the graphene and the substrate because the graphene is transferred to the substrate while floating in water. The trapped water molecules can cause the unwanted doping of graphene and hysteretic behavior in the current-voltage (I-V) curve. We here propose a new semidry transfer method using the Kapton tape as an additional flexible supporting layer. The N-2 blowing and heating processes are added to vaporize the water molecules adsorbed on graphene layer right before the transfer step. By comparing the I-V characteristics of wet-and semidry-transferred graphene field effect transistor (GFET), the field effect mobility is found to be larger for the semidry-transferred GFET in comparison with the wet-transferred one, possibly due to the more uniform Coulomb potential landscape. Most importantly, the hysteretic behavior is found to be reduced in accordance with the decrease of the trapped water molecules. The averaged electron mobilities obtained from the GFET measurements are 1118 cm(2)/Vs and 415 cm(2)/Vs for semidry- and wet-transferred graphene, respectively. Our semidry transfer method can provide a simple and reliable way to transfer the CVD graphene onto an arbitrary substrate with the minimized number of trapped water molecules, which is readily applicable for large-scale substrates with potential of commercialization.}, issn = {0021-8979}, doi = {10.1063/1.5089494}, author = {Jung, Sungchul and Yoon, Hoon Hahn and Jin, Hanbyul and Mo, Kyuhyung and Choi, Gahyun and Lee, Junghyun and Park, Hyesung and Park, Kibog} } @article { ISI:000503978100047, title = {Repeated measurements with minimally destructive partial-transfer absorption imaging}, journal = {Opt. Express}, volume = {27}, number = {25}, year = {2019}, month = {DEC 9}, pages = {36611-36624}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {We demonstrate partial-transfer absorption imaging as a technique for repeatedly imaging an ultracold atomic ensemble with minimal perturbation. We prepare an atomic cloud in a state that is dark to the imaging light. We then use a microwave pulse to coherently transfer a small fraction of the ensemble to a bright state, which we image using in situ absorption imaging. The amplitude or duration of the microwave pulse controls the fractional transfer from the dark to the bright state. For small transfer fractions, we can image the atomic cloud up to 50 times before it is depleted. As a sample application, we repeatedly image an atomic cloud oscillating in a dipole trap to measure the trap frequency. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement}, issn = {1094-4087}, doi = {10.1364/OE.27.036611}, author = {Seroka, Erin Marshall and Curiel, Ana Valdes and Trypogeorgos, Dimitrios and Lundblad, Nathan and Spielman, Ian B.} } @article { ISI:000500743400001, title = {Rydberg-Mediated Entanglement in a Two-Dimensional Neutral Atom Qubit Array}, journal = {Phys. Rev. Lett.}, volume = {123}, number = {23}, year = {2019}, month = {DEC 4}, pages = {230501}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We demonstrate high fidelity two-qubit Rydberg blockade and entanglement on a pair of sites in a large two-dimensional qubit array. The qubit array is defined by a grid of blue detuned lines of light with 121 sites for trapping atomic qubits. Improved experimental methods have increased the observed Bell state fidelity to F-Bell = 0.86(2). Accounting for errors in state preparation and measurement we infer a fidelity of F-(SPAM)(Bell) = 0.88. Accounting for errors in single qubit operations we infer that a Bell state created with the Rydberg mediated C-Z gate has a fidelity of F-Bell(CZ) = 0.89. Comparison with a detailed error model based on quantum process matrices indicates that finite atom temperature and laser noise are the dominant error sources contributing to the observed gate infidelity.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.123.230501}, author = {Graham, T. M. and Kwon, M. and Grinkemeyer, B. and Marra, Z. and Jiang, X. and Lichtman, M. T. and Sun, Y. and Ebert, M. and Saffman, M.} } @article {ISI:000482547000001, title = {Sauter-Schwinger effect with a quantum gas}, journal = {New J. Phys.}, volume = {21}, year = {2019}, month = {AUG 21}, pages = {083035}, publisher = {IOP PUBLISHING LTD}, type = {Article}, abstract = {The creation of particle-antiparticle pairs from vacuum by a large electric field is at the core of quantum electrodynamics. Despite the wide acceptance that this phenomenon occurs naturally when electric field strengths exceed E-c approximate to 10(18) Vm(-1), it has yet to be experimentally observed due to the limitations imposed by producing electric fields at this scale. The high degree of experimental control present in ultracold atomic systems allow experimentalists to create laboratory analogs to high-field phenomena. Here we emulated massive relativistic particles subject to large electric field strengths, thereby quantum-simulated particle-antiparticle pair creation, and experimentally explored particle creation from {\textquoteleft}the Dirac vacuum{\textquoteright}. Data collected from our analog system spans the full parameter regime from low applied field (negligible pair creation) below the Sauter-Schwinger limit, to high field (maximum rate of pair creation) far in excess of the Sauter-Schwinger limit. In our experiment, we perform direct measurements on an analog atomic system and show that this high-field phenomenon is well-characterized by Landau-Zener tunneling, well known in the atomic physics context, and we find full quantitative agreement with theory with no adjustable parameters.}, keywords = {particle creation, quantum gases, quantum simulation, Sauter-Schwinger effect}, issn = {1367-2630}, doi = {10.1088/1367-2630/ab3840}, author = {Pineiro, A. M. and Genkina, D. and Lu, Mingwu and Spielman, I. B.} } @article {ISI:000462935500003, title = {Scale-Invariant Continuous Entanglement Renormalization of a Chern Insulator}, journal = {Phys. Rev. Lett.}, volume = {122}, number = {12}, year = {2019}, month = {MAR 27}, pages = {120502}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The multiscale entanglement renormalization ansatz (MERA) postulates the existence of quantum circuits that renormalize entanglement in real space at different length scales. Chem insulators, however, cannot have scale-invariant discrete MERA circuits with a finite bond dimension. In this Letter, we show that the continuous MERA (cMERA), a modified version of MERA adapted for field theories, possesses a fixed point wave function with a nonzero Chern number. Additionally, it is well known that reversed MERA circuits can be used to prepare quantum states efficiently in time that scales logarithmically with the size of the system. However, state preparation via MERA typically requires the advent of a full-fledged universal quantum computer. In this Letter, we demonstrate that our cMERA circuit can potentially be realized in existing analog quantum computers, i.e., an ultracold atomic Fermi gas in an optical lattice with light-induced spin-orbit coupling.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.122.120502}, author = {Chu, Su-Kuan and Zhu, Guanyu and Garrison, James R. and Eldredge, Zachary and Curiel, Ana Valdes and Bienias, Przemyslaw and Spielman, I. B. and Gorshkov, V, Alexey} } @article { ISI:000501541900004, title = {Scanning tunneling Andreev microscopy of titanium nitride thin films}, journal = {Phys. Rev. B}, volume = {100}, number = {21}, year = {2019}, month = {DEC 9}, pages = {214505}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We report scanning tunneling microscopy results on 25- and 50-nm-thick films of superconducting TiN that show Andreev tunneling behavior at 0.5 K. At most locations on the topographically rough surfaces, we observe tip-sample current-voltage characteristics with a clear superconducting gap, as expected for superconductor-normal (S-N) tunneling through a low-transparency barrier, while in some places, we find a zero-voltage conductance peak, as expected for S-N Andreev tunneling through a highly transparent barrier. Fitting the Blonder-Tinkham-Klapwijk model to the conductance data allows an accurate extraction of the TiN superconducting gap Delta, by accounting for local variations in the tip-sample barrier height Z and junction temperature T. From spatial maps of the model parameters, we find that both films show a strong inhomogeneity, with Delta varying by as much as a factor of 2 from grain to grain. In the thicker film, however, correlations between T, Z, and Delta suggest the grains are thermally isolated, perhaps due to internal stress. We discuss possible mechanisms that could produce these large correlated variations, including local heating and surface contamination, and consider some of the implications for devices made from such films.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.100.214505}, author = {Liao, Wan-Ting and Kohler, T. P. and Osborn, K. D. and Butera, R. E. and Lobb, C. J. and Wellstood, F. C. and Dreyer, M.} } @article {ISI:000462882400010, title = {Scrambling in the Dicke model}, journal = {Phys. Rev. A}, volume = {99}, number = {4}, year = {2019}, month = {APR 1}, pages = {043602}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The scrambling rate lambda(L) associated with the exponential growth of out-of-time-ordered correlators can be used to characterize quantum chaos. Here we use a particular Majorana fermion representation of spin-1/2 systems to study quantum chaos in the Dicke model. We take the system to be in thermal equilibrium and compute lambda(L) throughout the phase diagram to leading order in 1/N. We find that the chaotic behavior is strongest close to the critical point. At high temperatures lambda(L) is nonzero over an extended region that includes both the normal and superradiant phases. At low temperatures lambda(L) is nonzero in (a) close vicinity of the critical point and (b) a region within the superradiant phase. In the process we also derive an effective theory for the superradiant phase at finite temperatures Our formalism does not rely on the assumption of total spin conservation.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.99.043602}, author = {Alavirad, Yahya and Lavasani, Ali} } @article {ISI:000471993700016, title = {The Search for Variation of Fundamental Constants with Clocks}, journal = {Ann. Phys.-Berlin}, volume = {531}, number = {5, SI}, year = {2019}, month = {MAY}, pages = {1800364}, publisher = {WILEY-V C H VERLAG GMBH}, type = {Article}, abstract = {In many theories beyond the Standard Model the quantities that we call {\textquoteleft}{\textquoteleft}fundamental constants{{\textquoteright}{\textquoteright}} become space-time dependent, leading to corresponding variation of atomic and molecular spectra and clock frequencies. The extraordinary improvement of the atomic clock precision in the past fifteen years enabled testing the constancy of the fundamental constant at a very high level of precision. Herein, searches for the variation of fundamental constants with clocks are discussed, focusing on recent key results and future proposals, including highly charged ion, molecular, and nuclear clocks. The relevance of the recent searches for oscillatory and transient variation of fundamental constants to the major unexplained phenomena of our Universe, the nature of dark matter, is discussed.}, keywords = {atomic clocks, highly charged ions, nuclear clock, variation of fundamental constants}, issn = {0003-3804}, doi = {10.1002/andp.201800364}, author = {Safronova, Marianna S.} } @article {ISI:000482530000002, title = {A semiclassical theory of phase-space dynamics of interacting bosons}, journal = {J. Phys. B-At. Mol. Opt. Phys.}, volume = {52}, number = {18}, year = {2019}, month = {SEP 28}, pages = {185302}, publisher = {IOP PUBLISHING LTD}, type = {Article}, abstract = {We study the phase-space representation of dynamics of bosons in the semiclassical regime where the occupation number of the modes is large. To this end, we employ the van Vleck-Gutzwiller propagator to obtain an approximation for the Green{\textquoteright}s function of the Wigner distribution. The semiclassical analysis incorporates interference of classical paths and reduces to the truncated Wigner approximation (TWA) when the interference is ignored. Furthermore, we identify the Ehrenfest time after which the TWA fails. As a case study, we consider a single-mode quantum nonlinear oscillator, which displays collapse and revival of observables. We analytically show that the interference of classical paths leads to revivals, an effect that is not reproduced by the TWA or a perturbative analysis.}, keywords = {Bose-Einstein condensates, phase-space dynamics, semiclassical physics}, issn = {0953-4075}, doi = {10.1088/1361-6455/ab319c}, author = {Mathew, R. and Tiesinga, E.} } @article {ISI:000470849000068, title = {Silicon photonic add-drop filter for quantum emitters}, journal = {Opt. Express}, volume = {27}, number = {12}, year = {2019}, month = {JUN 10}, pages = {16882-16889}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {Integration of single-photon sources and detectors to silicon-based photonics opens the possibility of complex circuits for quantum information processing. In this work. we demonstrate integration of quantum dots with a silicon photonic add-drop filter for on-chip filtering and muting of telecom photons. A silicon microdisk resonator acts as a narrow filter that transfers the quantum dot emission and filters the background over a wide wavelength range. Moreover, by tuning the quantum dot emission wavelength over the resonance of the microdisk, we can control the transmission of the quantum dot emission to the drop and through channels of the add-drop filter. This result is a step toward the on-chip control of single photons using silicon photonics for applications in quantum information processing. such as linear optical quantum computation and boson sampling. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement}, issn = {1094-4087}, doi = {10.1364/OE.27.016882}, author = {Aghaeimeibodi, Shahriar and Kim, Je-Hyung and Lee, Chang-Min and Buyukkaya, Mustafa Atabey and Richardson, Christopher and Waks, Edo} } @article {ISI:000478993000006, title = {Simulation of the coupling strength of capacitively coupled singlet-triplet qubits}, journal = {Phys. Rev. B}, volume = {100}, number = {7}, year = {2019}, month = {AUG 6}, pages = {075411}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We consider a system of two purely capacitively coupled singlet-triplet qubits and numerically simulate the energy structure of four electrons in two double quantum dots with a large potential barrier between them. We calculate the interqubit coupling strength using an extended Hund-Mulliken approach which includes excited orbitals in addition to the lowest-energy orbital for each quantum dot. We show the coupling strength as a function of the qubit separation as well as plotting it against the detunings of the two double quantum dots and show that the general qualitative features of our results can be captured by a potential-independent toy model of the system.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.100.075411}, author = {Buterakos, Donovan and Throckmorton, Robert E. and S. Das Sarma} } @article { ISI:000490353500045, title = {A Spin-Photon Interface Using Charge-Tunable Quantum Dots Strongly Coupled to a Cavity}, journal = {Nano Lett.}, volume = {19}, number = {10}, year = {2019}, month = {OCT}, pages = {7072-7077}, publisher = {AMER CHEMICAL SOC}, type = {Article}, abstract = {Charged quantum dots containing an electron or hole spin are bright solid-state qubits suitable for quantum networks and distributed quantum computing. Incorporating such quantum dot spin into a photonic crystal cavity creates a strong spin-photon interface in which the spin can control a photon by modulating the cavity reflection coefficient. However, previous demonstrations of such spin-photon interfaces have relied on quantum dots that are charged randomly by nearby impurities, leading to instability in the charge state, which causes poor contrast in the cavity reflectivity. Here we demonstrate a strong spin-photon interface using a quantum dot that is charged deterministically with a diode structure. By incorporating this actively charged quantum dot in a photonic crystal cavity, we achieve strong coupling between the cavity mode and the negatively charged state of the dot. Furthermore, by initializing the spin through optical pumping, we show strong spin-dependent modulation of the cavity reflectivity, corresponding to a cooperativity of 12. This spin-dependent reflectivity is important for mediating entanglement between spins using photons, as well as generating strong photon-photon interactions for applications in quantum networking and distributed quantum computing.}, keywords = {cavity quantum electrodynamics, Quantum Dots, single electron spin, strong light-matter interaction}, issn = {1530-6984}, doi = {10.1021/acs.nanolett.9b02443}, author = {Luo, Zhouchen and Sun, Shuo and Karasahin, Aziz and Bracker, Allan S. and Carter, Samuel G. and Yakes, Michael K. and Gammon, Daniel and Waks, Edo} } @article { ISI:000492332900005, title = {Stroboscopic approach to trapped-ion quantum information processing with squeezed phonons}, journal = {Phys. Rev. A}, volume = {100}, number = {4}, year = {2019}, month = {OCT 24}, pages = {043417}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {In trapped-ion quantum information processing, interactions between spins (qubits) are mediated by collective modes of motion of an ion crystal. While there are many different experimental strategies to design such interactions, they all face both technical and fundamental limitations to the achievable coherent interaction strength. In general, obtaining strong interactions and fast gates is an ongoing challenge. Here, we extend previous work {[}W. Ge, B. C. Sawyer, J. W. Britton, K. Jacobs, J. J. Bollinger, and M. Foss-Feig, Phys. Rev. Lett. 122, 030501 (2019)] and present a general strategy for enhancing the interaction strengths in trapped-ion systems via parametric amplification of the ions{\textquoteright} motion. Specifically, we propose a stroboscopic protocol using alternating applications of parametric amplification and spin-motion coupling. In comparison with the previous work, we show that the current protocol can lead to larger enhancements in the coherent interaction that increase exponentially with the gate time.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.100.043417}, author = {Ge, Wenchao and Sawyer, Brian C. and Britton, Joseph W. and Jacobs, Kurt and Foss-Feig, Michael and Bollinger, John J.} } @conference {ISI:000466478500026, title = {Structured neutron waves}, booktitle = {OPTICAL, OPTO-ATOMIC, AND ENTANGLEMENT-ENHANCED PRECISION METROLOGY}, series = {Proceedings of SPIE}, volume = {10934}, year = {2019}, note = {Conference on Optical, Opto-Atomic, and Entanglement-Enhanced Precision Metrology, San Francisco, CA, FEB 02-07, 2019}, pages = {1093425}, publisher = {SPIE}, organization = {SPIE}, type = {Proceedings Paper}, abstract = {Emerging quantum materials are becoming the building blocks for quantum devices and they are enabling new advances from spintronics to topological insulators. Their functionality typically comes from their inner magnetic field structure. Neutrons are a particularly good probe to characterize such features. The control of neutron orbital angular momentum and the spin-orbit interaction enables new characterizing techniques and increased sensitivity towards specific material properties. Here we review the preparation and characterization methods of structured neutron waves.}, keywords = {Neutron Interferometry, Neutrons, orbital angular momentum, spin-orbit states, Structured Waves}, isbn = {978-1-5106-2511-2}, issn = {0277-786X}, doi = {10.1117/12.2515469}, author = {Sarenac, Dusan and Clark, Charles W. and Cory, David G. and Kapahi, Connor and Heacock, Benjamin and Huber, Michael G. and Nsofini, Joachim and Shahi, Chandra B. and Pushin, Dmitry A.}, editor = {Shahriar, SM and Scheuer, J} } @article {ISI:000485761800002, title = {Superconductor versus insulator in twisted bilayer graphene}, journal = {Phys. Rev. B}, volume = {100}, number = {11}, year = {2019}, month = {SEP 13}, pages = {115128}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We present a simple model that we believe captures the key aspects of the competition between superconducting and insulating states in twisted bilayer graphene. Within this model, the superconducting phase is primary, and arises at generic fillings, but is interrupted by the insulator at commensurate fillings. Importantly, the insulator forms because of electron-electron interactions, but the model is agnostic as to the superconducting pairing mechanism, which need not originate with electron-electron interactions. The model is composed of a collection of crossed one-dimensional quantum wires whose intersections form a superlattice. At each superlattice point, we place a locally superconducting puddle which can exchange Cooper pairs with the quantum wires. We analyze this model assuming weak wire-puddle and wire-wire couplings. We show that for a range of repulsive intrawire interactions, the system is superconducting at {\textquoteleft}{\textquoteleft}generic{{\textquoteright}{\textquoteright}} incommensurate fillings, with the superconductivity being {\textquoteleft}{\textquoteleft}interrupted{{\textquoteright}{\textquoteright}} by an insulating phase at commensurate fillings. We further show that the gapped insulating states at commensurate fillings give way to gapless states upon application of external Zeeman fields. These features are consistent with experimental observations in magic-angle twisted bilayer graphenes despite the distinct microscopic details. We further study the full phase diagram of this model and discover that it contains several distinct correlated insulating states, which we characterize herein.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.100.115128}, author = {Chou, Yang-Zhi and Lin, Yu-Ping and S. Das Sarma and Nandkishore, Rahul M.} } @article { ISI:000492968000008, title = {Supercurrent interference in semiconductor nanowire Josephson junctions}, journal = {Phys. Rev. B}, volume = {100}, number = {15}, year = {2019}, month = {OCT 28}, pages = {155431}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Semiconductor-superconductor hybrid systems provide a promising platform for hosting unpaired Majorana fermions towards the realization of fault-tolerant topological quantum computing. In this study we employ the Keldysh nonequilibrium Green{\textquoteright}s function formalism to model quantum transport in normal-superconductor junctions. We analyze III-V semiconductor nanowire Josephson junctions (InAs/Nb) using a three-dimensional discrete lattice model described by the Bogoliubov-de Gennes Hamiltonian in the tight-binding approximation, and compute the Andreev bound state spectrum and current-phase relations. Recent experiments {[}Zuo et al., Phys. Rev. Lett. 119, 187704 (2017) and Gharavi et al., arXiv: 1405.7455] reveal critical current oscillations in these devices, and our simulations confirm these to be an interference effect of the transverse subbands in the nanowire. We add disorder to model coherent scattering and study its effect on the critical current oscillations, with an aim to gain a thorough understanding of the experiments. The oscillations in the disordered junction are highly sensitive to the particular realization of the random disorder potential, and to the gate voltage. A macroscopic current measurement thus gives us information about the microscopic profile of the junction. Finally, we study dephasing in the channel by including elastic phase-breaking interactions. The oscillations thus obtained are in good qualitative agreement with the experimental data, and this signifies the essential role of phase-breaking processes in III-V semiconductor nanowire Josephson junctions.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.100.155431}, author = {Sriram, Praveen and Kalantre, Sandesh S. and Gharavi, Kaveh and Baugh, Jonathan and Muralidharan, Bhaskaran} } @article { ISI:000459821800002, title = {Superstrong coupling in circuit quantum electrodynamics}, journal = {NPJ QUANTUM INFORMATION}, volume = {5}, year = {2019}, month = {FEB 25}, pages = {20}, issn = {2056-6387}, doi = {10.1038/s41534-019-0134-2}, author = {Kuzmin, Roman and Mehta, Nitish and Grabon, Nicholas and Mencia, Raymond and Manucharyan, Vladimir E.} } @article {ISI:000479034100005, title = {Suppressing Inhomogeneous Broadening in a Lutetium Multi-ion Optical Clock}, journal = {Phys. Rev. Lett.}, volume = {123}, number = {6}, year = {2019}, month = {AUG 7}, pages = {063201}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We demonstrate precision measurement and control of inhomogeneous broadening in a multi-ion clock consisting of three Lu-176(+) ions. Microwave spectroscopy between hyperfine states in the D-3(1) level is used to characterize differential systematic shifts between ions, most notably those associated with the electric quadrupole moment. By appropriate alignment of the magnetic field, we demonstrate suppression of these effects to the similar to 10(-17) level relative to the S-1(0) <-> D-3(1) optical transition frequency. Correlation spectroscopy on the optical transition demonstrates the feasibility of a 10-s Ramsey interrogation in the three ion configuration with a corresponding projection noise limited stability of sigma(tau) = 8.2 x 10(-17)/root tau.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.123.063201}, author = {Tan, T. R. and Kaewuam, R. and Arnold, K. J. and Chanu, S. R. and Zhang, Zhiqiang and Safronova, M. S. and Barrett, M. D.} } @article {ISI:000461940700022, title = {Switchable detector array scheme to reduce the effect of single-photon detector{\textquoteright}s deadtime in a multi-bit/photon quantum link}, journal = {Opt. Commun.}, volume = {441}, year = {2019}, month = {JUN 15}, pages = {132-137}, publisher = {ELSEVIER SCIENCE BV}, type = {Article}, abstract = {{We explore the use of a switchable single-photon detector (SPD) array scheme to reduce the effect of a detector{\textquoteright}s deadtime for a multi-bit/photon quantum link. The case of data encoding using M possible orbital-angular-momentum (OAM) states is specifically studied in this paper. Our method uses N SPDs with a controllable M x N optical switch and we use a Monte Carlo-based method to simulate the quantum detection process. The simulation results show that with the use of the switchable SPD array, the detection system can allow a higher incident photon rate than what might otherwise be limited by detectors{\textquoteright} deadtime. For the case of M = 4}, keywords = {orbital angular momentum, quantum communication, Single photon detection}, issn = {0030-4018}, doi = {10.1016/j.optcom.2019.01.081}, author = {Liu, Cong and Ren, Yongxiong and Zhao, Jiapeng and Mirhosseini, Mohammad and Rafsanjani, Seyed Mohammad Hashemi and Xie, Guodong and Pang, Kai and Song, Haoqian and Zhao, Zhe and Wang, Zhe and Li, Long and Bienfang, Joshua C. and Migdall, Alan and Brun, Todd A. and Tur, Moshe and Boyd, Robert W. and Willner, Alan E.} } @article { ISI:000489831000001, title = {Synthetic Gauge Field for Two-Dimensional Time-Multiplexed Quantum Random Walks}, journal = {Phys. Rev. Lett.}, volume = {123}, number = {15}, year = {2019}, month = {OCT 11}, pages = {150503}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Temporal multiplexing provides an efficient and scalable approach to realize a quantum random walk with photons that can exhibit topological properties. But two-dimensional time-multiplexed topological quantum walks studied so far have relied on generalizations of the Su-Shreiffer-Heeger model with no synthetic gauge field. In this work, we demonstrate a two-dimensional topological quantum random walk where the nontrivial topology is due to the presence of a synthetic gauge field. We show that the synthetic gauge field leads to the appearance of multiple band gaps and, consequently, a spatial confinement of the quantum walk distribution. Moreover, we demonstrate topological edge states at an interface between domains with opposite synthetic fields. Our results expand the range of Hamiltonians that can be simulated using photonic quantum walks.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.123.150503}, author = {Chalabi, Hamidreza and Barik, Sabyasachi and Mittal, Sunil and Murphy, Thomas E. and Hafezi, Mohammad and Waks, Edo} } @article {ISI:000455826000001, title = {Tabletop experiments for quantum gravity: a user{\textquoteright}s manual}, journal = {Class. Quantum Gravity}, volume = {36}, number = {3}, year = {2019}, month = {FEB 7}, pages = {034001}, publisher = {IOP PUBLISHING LTD}, type = {Article}, abstract = {Recent advances in cooling, control, and measurement of mechanical systems in the quantum regime have opened the possibility of the first direct observation of quantum gravity, at scales achievable in experiments. This paper gives a broad overview of this idea, using some matter-wave and optomechanical systems to illustrate the predictions of a variety of models of low-energy quantum gravity. We first review the treatment of perturbatively quantized general relativity as an effective quantum field theory, and consider the particular challenges of observing quantum effects in this framework. We then move on to a variety of alternative models, such as those in which gravity is classical, emergent, or responsible for a breakdown of quantum mechanics.}, keywords = {experimental tests, Optomechanics, quantum gravity}, issn = {0264-9381}, doi = {10.1088/1361-6382/aaf9ca}, author = {Carney, Daniel and Stamp, Philip C. E. and Taylor, Jacob M.} } @article {14281, title = {Theory of Bose condensation of light via laser cooling of atoms}, journal = {Phys. Rev. A}, volume = {99}, year = {2019}, month = {Mar}, pages = {031801}, author = {Wang, Chiao-Hsuan and Gullans, M. J. and Porto, J. V. and Phillips, William D. and Taylor, Jacob M.} } @article {ISI:000461896700001, title = {Theory of Bose condensation of light via laser cooling of atoms}, journal = {Phys. Rev. A}, volume = {99}, number = {3}, year = {2019}, month = {MAR 14}, pages = {031801}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {A Bose-Einstein condensate (BEC) is a quantum phase of matter achieved at low temperatures. Photons, one of the most prominent species of bosons, do not typically condense due to the lack of a particle number conservation. We recently described a photon thermalization mechanism which gives rise to a grand canonical ensemble of light with effective photon number conservation between a subsystem and a particle reservoir. This mechanism occurs during Doppler laser cooling of atoms where the atoms serve as a temperature reservoir while the cooling laser photons serve as a particle reservoir. In contrast to typical discussions of BEC, our system is better treated with a controlled chemical potential rather than a controlled particle number, and is subject to energy-dependent loss. Here, we address the question of the possibility of a BEC of photons in this laser cooling photon thermalization scenario and theoretically demonstrate that a Bose condensation of photons can be realized by cooling an ensemble of two-level atoms (realizable with alkaline-earth atoms) inside a Fabry-Perot cavity.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.99.031801}, author = {Wang, Chiao-Hsuan and Gullans, M. J. and Porto, V, J. and Phillips, William D. and Taylor, Jacob M.} } @article {ISI:000473009200001, title = {Theory of coherent phase modes in insulating Josephson junction chains}, journal = {Phys. Rev. B}, volume = {99}, number = {21}, year = {2019}, month = {JUN 21}, pages = {214509}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Recent microwave reflection measurements of Josephson junction chains have suggested the presence of nearly coherent collective charge oscillations deep in the insulating phase. Here we develop a qualitative understanding of such coherent charge modes by studying the local dynamical polarizability of the insulating phase of a finite length sine-Gordon model. By considering parameters near the noninteracting fermion limit where the charge operator dominantly couples to soliton-antisoliton pairs of the sine-Gordon model, we find that the local dynamical polarizability shows an array of sharp peaks in frequency representing coherent phase oscillations on top of an incoherent background. The strength of the coherent peaks relative to the incoherent background increases as a power law in frequency as well as exponentially as the Luttinger parameter approaches a critical value. The dynamical polarizability also clearly shows the insulating gap. We then compare the results in the high frequency limit to a perturbative estimate of phase-slip-induced decay of plasmons in the Josephson junction chain.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.214509}, author = {Wu, Huan-Kuang and Sau, Jay D.} } @article {ISI:000471983100001, title = {Thermal radiation as a probe of one-dimensional electron liquids}, journal = {Phys. Rev. B}, volume = {99}, number = {23}, year = {2019}, month = {JUN 11}, pages = {235124}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Motivated by recent developments in the field of plasmonics, we develop the theory of radiation from one-dimensional electron liquids, showing that the spectrum of thermal radiation emitted from the system exhibits signatures of non-Fermi liquid behavior. We derive a multipole expansion for the radiation based on the Tomonaga-Luttinger liquid model. While the dipole radiation pattern is determined by the conductivity of the system, we demonstrate that the quadrupole radiation can reveal important features of the quantum liquid, such as the Luttinger parameter. Radiation offers a probe of the interactions of the system, including Mott physics as well as nonlinear Luttinger liquid behavior. We show that these effects can be probed in current experiments on effectively one-dimensional electron liquids, such as carbon nanotubes.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.235124}, author = {DeGottardi, Wade and Gullans, Michael J. and Hegde, Suraj and Vishveshwara, Smitha and Hafezi, Mohammad} } @article {ISI:000464711300007, title = {Tools for designing atom interferometers in a microgravity environment}, journal = {Phys. Rev. A}, volume = {99}, number = {4}, year = {2019}, month = {APR 15}, pages = {043615}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We present a variational model suitable for rapid preliminary design of atom interferometers in a microgravity environment. The model approximates the solution of the three-dimensional rotating-frame Gross-Pitaevskii equation as the sum of N-c Gaussian clouds. Each Gaussian cloud is assumed to have time-dependent center positions, widths, and linear and quadratic phase parameters. We applied the Lagrangian variational method (LVM) with this trial wave function to derive equations of motion for these parameters that can be adapted to any external potential. We also present a one-dimensional (1D) version of this variational model. As an example we apply the model to a 1D atom interferometry scheme for measuring Newton{\textquoteright}s gravitational constant, G, in a microgravity environment. We show how the LVM model can (1) constrain the experimental parameter space size, (2) show how the value of G can be obtained from the experimental conditions and interference pattern characteristics, and (3) show how to improve the sensitivity of the measurement and construct a preliminary error budget.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.99.043615}, author = {Ashwood, Elizabeth and Wells, Ed Wesley and Kurkcuoglu, Doga Murat and Sapp, Robert Colson and Clark, Charles W. and Edwards, Mark} } @article {ISI:000462967000001, title = {Topological bands for ultracold atoms}, journal = {Rev. Mod. Phys.}, volume = {91}, number = {1}, year = {2019}, month = {MAR 25}, pages = {015005}, publisher = {AMER PHYSICAL SOC}, type = {Review}, abstract = {There have been significant recent advances in realizing band structures with geometrical and topological features in experiments on cold atomic gases. This review summarizes these developments, beginning with a summary of the key concepts of geometry and topology for Bloch bands. Descriptions are given of the different methods that have been used to generate these novel band structures for cold atoms and of the physical observables that have allowed their characterization. The focus is on the physical principles that underlie the different experimental approaches, providing a conceptual framework within which to view these developments. Also described is how specific experimental implementations can influence physical properties. Moving beyond single-particle effects, descriptions are given of the forms of interparticle interactions that emerge when atoms are subjected to these energy bands and of some of the many-body phases that may be sought in future experiments.}, issn = {0034-6861}, doi = {10.1103/RevModPhys.91.015005}, author = {Cooper, N. R. and Dalibard, J. and Spielman, I. B.} } @article {ISI:000467383900001, title = {Topological chiral superconductivity with spontaneous vortices and supercurrent in twisted bilayer graphene}, journal = {Phys. Rev. B}, volume = {99}, number = {19}, year = {2019}, month = {MAY 8}, pages = {195114}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study d-wave superconductivity in twisted bilayer graphene and reveal phenomena that arise due to the moire superlattice. In the d-wave pairing, the relative motion (RM) of two electrons in a Cooper pair can have either d + id or d - id symmetry with opposite angular momenta. Due to the enlarged moire superlattice, the center-of-mass motion (COMM) can also carry a finite angular momentum while preserving the moire periodicity. By matching the total angular momentum, which has contributions from both the RM and the COMM, Cooper pairs with d + id and d - id RMs are intrinsically coupled in a way such that the COMM associated with one of the RMs has a spontaneous vortex-antivortex lattice configuration. Another phenomenon is that the chiral d-wave state carries spontaneous bulk circulating supercurrent. The chiral d-wave superconductors are gapped and also topological as characterized by an integer Chern number. Nematic d-wave superconductors, which could be stabilized, for example, by uniaxial strain, are gapless with point nodes.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.195114}, author = {Wu, Fengcheng} } @article {ISI:000459920900007, title = {Topological Insulators in Twisted Transition Metal Dichalcogenide Homobilayers}, journal = {Phys. Rev. Lett.}, volume = {122}, number = {8}, year = {2019}, month = {FEB 28}, pages = {086402}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We show that moire bands of twisted homobilayers can be topologically nontrivial, and illustrate the tendency by studying valence band states in +/- K valleys of twisted bilayer transition metal dichalcogenides, in particular, bilayer MoTe2. Because of the large spin-orbit splitting at the monolayer valence band maxima, the low energy valence states of the twisted bilayer MoTe2 at the +K (-K) valley can be described using a two-band model with a layer-pseudospin magnetic field Delta(r) that has the moire period. We show that Delta(r) has a topologically nontrivial skyrmion lattice texture in real space, and that the topmost moire valence bands provide a realization of the Kane-Mele quantum spin-Hall model, i. e., the two-dimensional time-reversal-invariant topological insulator. Because the bands narrow at small twist angles, a rich set of broken symmetry insulating states can occur at integer numbers of electrons per moire cell.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.122.086402}, author = {Wu, Fengcheng and Lovorn, Timothy and Tutuc, Emanuel and Martin, Ivar and MacDonald, A. H.} } @article {ISI:000474394600005, title = {Topological nanomaterials}, journal = {Nat. Rev. Mater.}, volume = {4}, number = {7}, year = {2019}, month = {JUL}, pages = {479-496}, publisher = {NATURE PUBLISHING GROUP}, type = {Review}, abstract = {The past decade has witnessed the emergence of a new frontier in condensed matter physics: topological materials with an electronic band structure belonging to a different topological class from that of ordinary insulators and metals. This non-trivial band topology gives rise to robust, spin-polarized electronic states with linear energy-momentum dispersion at the edge or surface of the materials. For topological materials to be useful in electronic devices, precise control and accurate detection of the topological states must be achieved in nanostructures, which can enhance the topological states because of their large surface-to-volume ratios. In this Review, we discuss notable synthesis and electron transport results of topological nanomaterials, from topological insulator nanoribbons and plates to topological crystalline insulator nanowires and Weyl and Dirac semimetal nanobelts. We also survey superconductivity in topological nanowires, a nanostructure platform that might enable the controlled creation of Majorana bound states for robust quantum computations. Two material systems that can host Majorana bound states are compared: spin-orbit coupled semiconducting nanowires and topological insulating nanowires, a focus of this Review. Finally, we consider the materials and measurement challenges that must be overcome before topological nanomaterials can be used in next-generation electronic devices.

}, issn = {2058-8437}, doi = {10.1038/s41578-019-0113-4}, author = {Liu, Pengzi and James R. Williams and Cha, Judy J.} } @article {ISI:000462967000002, title = {Topological photonics}, journal = {Rev. Mod. Phys.}, volume = {91}, number = {1}, year = {2019}, month = {MAR 25}, pages = {015006}, publisher = {AMER PHYSICAL SOC}, type = {Review}, abstract = {Topological photonics is a rapidly emerging field of research in which geometrical and topological ideas are exploited to design and control the behavior of light. Drawing inspiration from the discovery of the quantum Hall effects and topological insulators in condensed matter, recent advances have shown how to engineer analogous effects also for photons, leading to remarkable phenomena such as the robust unidirectional propagation of light, which hold great promise for applications. Thanks to the flexibility and diversity of photonics systems, this field is also opening up new opportunities to realize exotic topological models and to probe and exploit topological effects in new ways. This article reviews experimental and theoretical developments in topological photonics across a wide range of experimental platforms, including photonic crystals, waveguides, metamaterials, cavities, optomechanics, silicon photonics, and circuit QED. A discussion of how changing the dimensionality and symmetries of photonics systems has allowed for the realization of different topological phases is offered, and progress in understanding the interplay of topology with non-Hermitian effects, such as dissipation, is reviewed. As an exciting perspective, topological photonics can be combined with optical nonlinearities, leading toward new collective phenomena and novel strongly correlated states of light, such as an analog of the fractional quantum Hall effect.}, issn = {0034-6861}, doi = {10.1103/RevModPhys.91.015006}, author = {Ozawa, Tomoki and Price, Hannah M. and Amo, Alberto and Goldman, Nathan and Hafezi, Mohammad and Lu, Ling and Rechtsman, Mikael C. and Schuster, David and Simon, Jonathan and Zilberberg, Oded and Carusotto, Iacopo} } @article { ISI:000502778700003, title = {Toward convergence of effective-field-theory simulations on digital quantum computers}, journal = {Phys. Rev. A}, volume = {100}, number = {6}, year = {2019}, month = {DEC 16}, pages = {062319}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We report results for simulating an effective field theory to compute the binding energy of the deuteron nucleus using a hybrid algorithm on a trapped-ion quantum computer. Two increasingly complex unitary coupled-cluster ansatze have been used to compute the binding energy to within a few percent for successively more complex Hamiltonians. By increasing the complexity of the Hamiltonian, allowing more terms in the effective field theory expansion, and calculating their expectation values, we present a benchmark for quantum computers based on their ability to scalably calculate the effective field theory with increasing accuracy. Our result of E-4 = - 2.220 +/- 0.179 MeV may be compared with the exact deuteron ground-state energy -2.224 MeV. We also demonstrate an error mitigation technique using Richardson extrapolation on ion traps. The error mitigation circuit represents a record for deepest quantum circuit on a trapped-ion quantum computer.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.100.062319}, author = {Shehab, O. and Landsman, K. and Nam, Y. and Zhu, D. and Linke, N. M. and Keesan, M. and Pooser, R. C. and Monroe, C.} } @conference {ISI:000482226302343, title = {Toward experimental implementation of quantum-enabled, bandwidth and power efficient communications}, booktitle = {2019 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO)}, series = {Conference on Lasers and Electro-Optics}, year = {2019}, note = {Conference on Lasers and Electro-Optics (CLEO), San Jose, CA, MAY 05-10, 2019}, publisher = {IEEE; AdValue Photon; Amer Elements; Class5 Photon; Coherent; GoFoton; Light Convers; LightTrans; MKS; OZ Opt Online; Santec; ThorLabs; UQDevices; YSL Photon}, organization = {IEEE; AdValue Photon; Amer Elements; Class5 Photon; Coherent; GoFoton; Light Convers; LightTrans; MKS; OZ Opt Online; Santec; ThorLabs; UQDevices; YSL Photon}, type = {Proceedings Paper}, abstract = {Coherent Frequency Shift Keying (CFSK) protocols paired with a quantum receiver can significantly optimize power and bandwidth efficiency of communication channels. We present our preliminary experimental data obtained with the CFSK quantum communication testbed. (c) 2019 The Author(s)}, isbn = {978-1-943580-57-6}, issn = {2160-9020}, author = {Burenkov, Ivan A. and Jabir, M. V. and El Idrissi, Driss and Battou, Abdella and Polyakov, Sergey V.} } @article { ISI:000489954500050, title = {Towards an in situ, full-power gauge of the focal-volume intensity of petawatt-class lasers}, journal = {Opt. Express}, volume = {27}, number = {21}, year = {2019}, month = {OCT 14}, pages = {30020-30030}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {About 50 years ago, Sarachick and Schappert {[}Phys. Rev. D. 1, 2738-2752 (1970)] showed that relativistic Thomson scattering leads to wavelength shifts that are proportional to the laser intensity. About 28 years later, Chen et al. {[}Nature 396, 653-655 (1998)] used these shifts to estimate their laser intensity near 10(18) W/cm(2). More recently, there have been several theoretical studies aimed at exploiting nonlinear Thomson scattering as a tool for direct measurement of intensities well into the relativistic regime. We present the first quantitative study of this approach for intensities between 10(18) and 10(19) W/cm(2). We show that the spectral shifts are in reasonable agreement with estimates of the peak intensity extracted from images of the focal area obtained at reduced power. Finally, we discuss the viability of the approach, its range of usefulness and how it might be extended to gauge intensities well in excess of 10(19) W/cm(2). (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement}, issn = {1094-4087}, doi = {10.1364/OE.27.030020}, author = {He, C. Z. and Longman, A. and Perez-Hernandez, J. A. and de Marco, M. and Salgado, C. and Zeraouli, G. and Gatti, G. and Roso, L. and Fedosejevs, R. and Hill, III, W. T.} } @article {14841, title = {Training of quantum circuits on a hybrid quantum computer}, journal = {Science Advances}, volume = {5}, year = {2019}, abstract = {Generative modeling is a flavor of machine learning with applications ranging from computer vision to chemical design. It is expected to be one of the techniques most suited to take advantage of the additional resources provided by near-term quantum computers. Here, we implement a data-driven quantum circuit training algorithm on the canonical Bars-and-Stripes dataset using a quantum-classical hybrid machine. The training proceeds by running parameterized circuits on a trapped ion quantum computer and feeding the results to a classical optimizer. We apply two separate strategies, Particle Swarm and Bayesian optimization to this task. We show that the convergence of the quantum circuit to the target distribution depends critically on both the quantum hardware and classical optimization strategy. Our study represents the first successful training of a high-dimensional universal quantum circuit and highlights the promise and challenges associated with hybrid learning schemes.

}, doi = {10.1126/sciadv.aaw9918}, url = {https://advances.sciencemag.org/content/5/10/eaaw9918}, author = {Zhu, D. and Linke, N. M. and Benedetti, M. and Landsman, K. A. and Nguyen, N. H. and Alderete, C. H. and Perdomo-Ortiz, A. and Korda, N. and Garfoot, A. and Brecque, C. and Egan, L. and Perdomo, O. and Monroe, C.} } @article {ISI:000456782500003, title = {Trapped Ion Quantum Information Processing with Squeezed Phonons}, journal = {Phys. Rev. Lett.}, volume = {122}, number = {3}, year = {2019}, month = {JAN 24}, pages = {030501}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Trapped ions offer a pristine platform for quantum computation and simulation, but improving their coherence remains a crucial challenge. Here, we propose and analyze a new strategy to enhance the coherent interactions in trapped ion systems via parametric amplification of the ions{\textquoteright} motion-by squeezing the collective motional modes (phonons), the spin-spin interactions they mediate can be significantly enhanced. We illustrate the power of this approach by showing how it can enhance collective spin states useful for quantum metrology, and how it can improve the speed and fidelity of two-qubit gates in multi-ion systems, important ingredients for scalable trapped ion quantum computation. Our results are also directly relevant to numerous other physical platforms in which spin interactions are mediated by bosons.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.122.030501}, author = {Ge, Wenchao and Sawyer, Brian C. and Britton, Joseph W. and Jacobs, Kurt and Bollinger, John J. and Foss-Feig, Michael} } @article { ISI:000498896500003, title = {Tunable Quantum Beat of Single Photons Enabled by Nonlinear Nanophotonics}, journal = {Phys. Rev. Appl.}, volume = {12}, number = {5}, year = {2019}, month = {NOV 22}, pages = {054054}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We demonstrate the tunable quantum beat of single photons through the co-development of core nonlinear nanophotonic technologies for frequency-domain manipulation of quantum states in a common physical platform. Spontaneous four-wave mixing in a nonlinear resonator is used to produce nondegenerate, quantum-correlated photon pairs. One photon from each pair is then frequency shifted, without degradation of photon statistics, using four-wave-mixing Bragg scattering in a second nonlinear resonator. Fine tuning of the applied frequency shift enables tunable quantum interference of the two photons as they are impinged on a beam splitter, with an oscillating signature that depends on their frequency difference. Our work showcases the potential of nonlinear nanophotonic devices as a valuable resource for photonic quantum-information science.}, issn = {2331-7019}, doi = {10.1103/PhysRevApplied.12.054054}, author = {Li, Qing and Singh, Anshuman and Lu, Xiyuan and Lawall, John and Verma, Varun and Mirin, Richard and Nam, Sae Woo and Srinivasan, Kartik} } @article {ISI:000460722900001, title = {Tunable surface plasmons in Weyl semimetals TaAs and NbAs}, journal = {Phys. Rev. B}, volume = {99}, number = {12}, year = {2019}, month = {MAR 4}, pages = {121401}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {By means of high-resolution electron energy loss spectroscopy, we investigate the low-energy excitation spectrum of transition-metal monopnictides hosting Weyl fermions. We observe gapped plasmonic modes in (001)-oriented surfaces of single crystals of NbAs and TaAs at 66 and 68 meV, respectively. Our findings are consistent with theory and we estimate an effective Coulomb interaction strength alpha(eff) approximate to 0.41 for both samples. We also demonstrate that the modification of the surface of transition-metal monopnictides by the adsorption of chemical species (in our case, oxygen and hydrocarbon fragments) changes the frequency of the plasmonic excitations, with a subsequent modification of the effective interaction strength in the 0.30-0.48 range. The remarkable dependence of plasmonic features on the presence of adsorbates paves the way for plasmonic sensors based on Weyl semimetals operating in the mid-infrared.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.121401}, author = {Chiarello, Gennaro and Hofmann, Johannes and Li, Zhilin and Fabio, Vito and Guo, Liwei and Chen, Xiaolong and S. Das Sarma and Politano, Antonio} } @article {ISI:000459152800093, title = {Twin-beam intensity-difference squeezing below 10 Hz}, journal = {Opt. Express}, volume = {27}, number = {4}, year = {2019}, month = {FEB 18}, pages = {4769-4780}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {We report the generation of strong, bright-beam intensity-difference squeezing down to measurement frequencies below 10 Hz. We generate two-mode squeezing in a four-wave mixing (4WM) process in Rb vapor, where the single-pass-gain nonlinear process does not require cavity locking and only relies on passive stability. We use diode laser technology and several techniques, including dual seeding, to remove the noise introduced by seeding the 4WM process as well as the background noise. Twin-beam intensity-difference squeezing down to frequencies limited only by the mechanical and atmospheric stability of the lab is achieved. These results should enable important low-frequency applications such as direct intensity-difference imaging with bright beams on integrating detectors. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement}, issn = {1094-4087}, doi = {10.1364/OE.27.004769}, author = {Wu, Meng-Chang and Schmittberger, Bonnie L. and Brewer, Nicholas R. and Speirs, Rory W. and Jones, Kevin M. and Lett, Paul D.} } @article { ISI:000489954500118, title = {Twin-beam sub-shot-noise raster-scanning microscope}, journal = {Opt. Express}, volume = {27}, number = {21}, year = {2019}, month = {OCT 14}, pages = {30810-30818}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {By exploiting the quantised nature of light, we demonstrate a sub-shot-noise scanning optical transmittance microscope. Our microscope demonstrates, with micron scale resolution, a factor of improvement in precision of 1.76(9) in transmittance estimation gained per probe photon relative to the theoretical model, a shot-noise-limited source of light, in an equivalent single-pass classical version of the same experiment using the same number of photons detected with a 90\% efficient detector. This would allow us to observe photosensitive samples with nearly twice the precision, without sacrificing image resolution or increasing optical power to improve signal-to-noise ratio. Our setup uses correlated twin-beams produced by parametric down-conversion, and a hybrid detection scheme comprising photon-counting-based feed-forward and a highly efficient CCD camera. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article{\textquoteright}s title, journal citation, and DOI.}, issn = {1094-4087}, doi = {10.1364/OE.27.030810}, author = {Sabines-Chesterking, J. and McMillan, A. R. and Moreau, P. A. and Joshi, S. K. and Knauer, S. and Johnston, E. and Rarity, J. G. and Matthews, J. C. F.} } @article {ISI:000484374000010, title = {Two are better than one}, journal = {Nat. Phys.}, volume = {15}, number = {9}, year = {2019}, month = {SEP}, pages = {882-883}, publisher = {NATURE PUBLISHING GROUP}, type = {News Item}, abstract = {Two-level quantum systems are routinely excited by resonant pump beams. Experiments now show resonant excitation through dichromatic, detuned pumps - providing a coherent control technique that will also aid single-photon emission from solid-state devices.}, issn = {1745-2473}, doi = {10.1038/s41567-019-0566-9}, author = {Solomon, Glenn S.} } @article { ISI:000492838300012, title = {Two-dimensional dilaton gravity theory and lattice Schwarzian theory}, journal = {Int. J. Mod. Phys. A}, volume = {34}, number = {29}, year = {2019}, month = {OCT 20}, pages = {1950176}, publisher = {WORLD SCIENTIFIC PUBL CO PTE LTD}, type = {Article}, abstract = {We report a holographic study of a two-dimensional dilaton gravity theory with the Dirichlet boundary condition for the cases of nonvanishing and vanishing cosmological constants. Our result shows that the boundary theory of the two-dimensional dilaton gravity theory with the Dirichlet boundary condition for the case of nonvanishing cosmological constants is the Schwarzian term coupled to a dilaton field, while for the case of vanishing cosmological constant, a theory does not have a kinetic term. We also include the higher derivative term R-2, where R is the scalar curvature that is coupled to a dilaton field. We find that the form of the boundary theory is not modified perturbatively. Finally, we show that a lattice holographic picture is realized up to the second-order perturbation of boundary cutoff epsilon(2) under a constant boundary dilaton field and the nonvanishing cosmological constant by identifying the lattice spacing a of a lattice Schwarzian theory with the boundary cutoff epsilon of the two-dimensional dilaton gravity theory.}, keywords = {Dilaton gravity theory, higher derivative term, isometry, lattice Schwarzian theory}, issn = {0217-751X}, doi = {10.1142/S0217751X19501768}, author = {Chu, Su-Kuan and Ma, Chen-Te and Wu, Chih-Hung} } @article {ISI:000455163900004, title = {Two-kind boson mixture honeycomb Hamiltonian of Bloch exciton-polaritons}, journal = {Phys. Rev. B}, volume = {99}, number = {4}, year = {2019}, month = {JAN 8}, pages = {045302}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The electronic band structure of a solid is a collection of allowed bands separated by forbidden bands, revealing the geometric symmetry of the crystal structures. Comprehensive knowledge of the band structure with band parameters explains intrinsic physical, chemical, and mechanical properties of the solid. Here we report the artificial polaritonic band structures of two-dimensional honeycomb lattices for microcavity exciton-polaritons using GaAs semiconductors in the wide-range detuning values, from cavity photonlike (red-detuned) to excitonlike (blue-detuned) regimes. In order to understand the experimental band structures and their band parameters, such as gap energies, bandwidths, hopping integrals, and density of states, we originally establish a polariton band theory within an augmented plane wave method with two-kind bosons, cavity photons trapped at the lattice sites, and freely moving excitons. In particular, this two-kind band theory is absolutely essential to elucidate the exciton effect in the band structures of blue-detuned exciton-polaritons, where the flattened excitonlike dispersion appears at larger in-plane momentum values captured in our experimental access window. We reach an excellent agreement between theory and experiments in all detuning values.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.045302}, author = {Pan, Haining and Winkler, K. and Powlowski, Mats and Xie, Ming and Schade, A. and Emmerling, M. and Kamp, M. and Klembt, S. and Schneider, C. and Byrnes, Tim and Hoefling, S. and Kim, Na Young} } @article {ISI:000482579500007, title = {Two-qubit entangling gates within arbitrarily long chains of trapped ions}, journal = {Phys. Rev. A}, volume = {100}, number = {2}, year = {2019}, month = {AUG 26}, pages = {022332}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Ion trap quantum computers are based on modulating the Coulomb interaction between atomic ion qubits using external forces. However, the spectral crowding of collective motional modes could pose a challenge to the control of such interactions for large numbers of qubits. Here, we show that high-fidelity quantum gate operations are still possible with very large trapped ion crystals by using a small and fixed number of motional modes, simplifying the scaling of ion trap quantum computers. We present analytical work that shows that gate operations need not couple to the motion of distant ions, allowing parallel entangling gates with a crosstalk error that falls off as the inverse cube of the distance between the pairs. We also experimentally demonstrate high-fidelity entangling gates on a fully connected set of seventeen Yb-171(+) qubits using simple laser pulse shapes that primarily couple to just a few modes.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.100.022332}, author = {Landsman, K. A. and Wu, Y. and Leung, P. H. and Zhu, D. and Linke, N. M. and Brown, K. R. and Duan, L. and Monroe, C.} } @article {ISI:000482583200042, title = {Two-Terminal and Multi-Terminal Designs for Next-Generation Quantized Hall Resistance Standards: Contact Material and Geometry}, journal = {IEEE Trans. Electron Devices}, volume = {66}, number = {9}, year = {2019}, month = {SEP}, pages = {3973-3977}, publisher = {IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC}, type = {Article}, abstract = {In this paper, we show that quantum Hall resistance measurements using two terminals may be as precise as four-terminal measurements when applying superconducting split contacts. The described sample designs eliminate resistance contributions of terminals and contacts such that the size and complexity of next-generation quantized Hall resistance devices can be significantly improved.}, keywords = {Epitaxial graphene (EG), multi-series (MS) contacts, quantized Hall resistance (QHR) standards, quantum Hall effect (QHE), superconducting contacts}, issn = {0018-9383}, doi = {10.1109/TED.2019.2926684}, author = {Kruskopf, Mattias and Rigosi, Albert F. and Panna, Alireza R. and Patel, Dinesh K. and Jin, Hanbyul and Marzano, Martina and Berilla, Michael and Newell, David B. and Elmquist, Randolph E.} } @article {ISI:000475499200001, title = {Universal level statistics of the out-of-time-ordered operator}, journal = {Phys. Rev. B}, volume = {100}, number = {3}, year = {2019}, month = {JUL 15}, pages = {035112}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The out-of-time-ordered correlator has been proposed as an indicator of chaos in quantum systems due to its simple interpretation in the semiclassical limit. In particular, its rate of possible exponential growth at h -> 0 is closely related to the classical Lyapunov exponent. Here we explore how this approach to quantum chaos relates to the random-matrix theoretical description. To do so, we introduce and study the level statistics of the logarithm of the out-of-time-ordered operator, (Lambda) over cap (t) = In (-{[}(x) over cap (t),(p) over cap (x)(0)](2) )/(2t), that we dub the {\textquoteleft}{\textquoteleft}Lyapunovian{{\textquoteright}{\textquoteright}} or {\textquoteleft}{\textquoteleft}Lyapunov operator{{\textquoteright}{\textquoteright}} for brevity. The Lyapunovian{\textquoteright}s level statistics is calculated explicitly for the quantum stadium billiard. It is shown that in the bulk of the filtered spectrum, this statistics perfectly aligns with the Wigner-Dyson distribution. One of the advantages of looking at the spectral statistics of this operator is that it has a well-defined semiclassical limit where it reduces to the matrix of uncorrelated classical finite-time Lyapunov exponents in a partitioned phase space. We provide a heuristic picture interpolating these two limits using Moyal quantum mechanics. Our results show that the Lyapunov operator may serve as a useful tool to characterize quantum chaos and in particular quantum-to-classical correspondence in chaotic systems by connecting the semiclassical Lyapunov growth at early times, when the quantum effects are weak, to universal level repulsion that hinges on strong quantum interference effects.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.100.035112}, author = {Rozenbaum, Efim B. and Ganeshan, Sriram and Galitski, Victor} } @article {ISI:000482956700001, title = {Universal logical gates with constant overhead: instantaneous Dehn twists for hyperbolic quantum codes}, journal = {Quantum}, volume = {3}, year = {2019}, month = {JUL 26}, publisher = {VEREIN FORDERUNG OPEN ACCESS PUBLIZIERENS QUANTENWISSENSCHAF}, type = {Article}, abstract = {A basic question in the theory of fault-tolerant quantum computation is to understand the fundamental resource costs for performing a universal logical set of gates on encoded qubits to arbitrary accuracy. Here we consider qubits encoded with constant space overhead (i.e. finite encoding rate) in the limit of arbitrarily large code distance d through the use of topological codes associated to triangulations of hyperbolic surfaces. We introduce explicit protocols to demonstrate how Dehn twists of the hyperbolic surface can be implemented on the code through constant depth unitary circuits, without increasing the space overhead. The circuit for a given Dehn twist consists of a permutation of physical qubits, followed by a constant depth local unitary circuit, where locality here is defined with respect to a hyperbolic metric that defines the code. Applying our results to the hyperbolic Fibonacci Turaev-Viro code implies the possibility of applying universal logical gate sets on encoded qubits through constant depth unitary circuits and with constant space overhead. Our circuits are inherently protected from errors as they map local operators to local operators while changing the size of their support by at most a constant factor; in the presence of noisy syndrome measurements, our results suggest the possibility of universal fault tolerant quantum computation with constant space overhead and time overhead of O(d/log d). For quantum circuits that allow parallel gate operations, this yields the optimal scaling of space-time overhead known to date.}, issn = {2521-327X}, author = {Lavasani, Ali and Zhu, Guanyu and Barkeshli, Maissam} } @article {ISI:000464281100001, title = {Universal Scattering of Ultracold Atoms and Molecules in Optical Potentials}, journal = {Atoms}, volume = {7}, number = {1}, year = {2019}, month = {MAR 15}, pages = {36}, publisher = {MDPI}, type = {Article}, abstract = {Universal collisions describe the reaction of molecules and atoms as dominated by long-range interparticle interactions. Here, we calculate the universal inelastic rate coefficients for a large group of ultracold polar molecules in their lower ro-vibrational states colliding with one of their constituent atoms. The rate coefficients are solely determined by values of the dispersion coefficient and reduced mass of the collisional system. We use the ab initio coupled-cluster linear response method to compute dynamic molecular polarizabilities and obtain the dispersion coefficients for some of the collisional partners and use values from the literature for others. Our polarizability calculations agree well with available experimental measurements. Comparison of our inelastic rate coefficients with results of numerically exact quantum-mechanical calculations leads us to conjecture that collisions with heavier atoms can be expected to be more universal.}, keywords = {chemical reactions, dispersion interaction, dynamic polorizability, ultracold atom-molecule collisions, universal model, van der Waals coefficients}, issn = {2218-2004}, doi = {10.3390/atoms7010036}, author = {Li, Hui and Li, Ming and Makrides, Constantinos and Petrov, Alexander and Kotochigova, Svetlana} } @article {ISI:000459572900004, title = {The US National Quantum Initiative}, journal = {Quantum Sci. Technol.}, volume = {4}, number = {2}, year = {2019}, month = {APR}, pages = {020504}, publisher = {IOP PUBLISHING LTD}, type = {Article}, abstract = {Quantum technology exploits the unique quantum features of superposition, entanglement, and fundamental metrology metrics in order to create new opportunities in secure communication, high-precision sensing, and revolutionary computers. Quantum technology may eventually underlie a whole new technological infrastructure, much as the semiconductor revolution changed everything in last half of the 20th century. This paper summarizes the motivations and goals for the National Quantum Initiative (NQI) in the United States, and describes some of the processes that led to the introduction and passage of legislation in the US Congress to create the NQI.}, issn = {2058-9565}, doi = {10.1088/2058-9565/ab0441}, author = {Raymer, Michael G. and Monroe, Christopher} } @article { ISI:000515524300011, title = {Use of quantum effects as potential qualifying metrics for "quantum grade silicon"}, journal = {AIP Adv.}, volume = {9}, number = {12}, year = {2019}, month = {DEC 1}, pages = {125153}, publisher = {AMER INST PHYSICS}, type = {Article}, abstract = {Across solid state quantum information, material deficiencies limit performance through enhanced relaxation, charge defect motion, or isotopic spin noise. While classical measurements of device performance provide cursory guidance, specific qualifying metrics and measurements applicable to quantum devices are needed. For quantum applications, new material metrics, e.g., enrichment, are needed, while existing classical metrics such as mobility might be relaxed compared to conventional electronics. In this work, we examine locally grown silicon that is superior in enrichment, but inferior in chemical purity compared to commercial-silicon, as part of an effort to underpin the material standards needed for quantum grade silicon and establish a standard approach for the intercomparison of these materials. We use a custom, mass-selected ion beam deposition technique, which has produced isotopic enrichment levels up to 99.999 98\% Si-28, to isotopically enrich Si-28, but with chemical purity \>99.97\% due to the molecular beam epitaxy techniques used. From this epitaxial silicon, we fabricate top-gated Hall bar devices simultaneously on Si-28 and on the adjacent natural abundance Si substrate for intercomparison. Using standard-methods, we measure maximum mobilities of approximate to(1740 +/- 2) cm(2)/(V s) at an electron density of (2.7 x 10(12) +/- 3 x 10(8)) cm(-2) and approximate to(6040 +/- 3) cm(2)/(V s) at an electron density of (1.2 x 10(12) +/- 5 x 10(8)) cm(-2) at T = 1.9 K for devices fabricated on Si-28 and Si-nat, respectively. For magnetic fields B \> 2 T, both devices demonstrate well developed Shubnikov-de Haas oscillations in the longitudinal magnetoresistance. This provides the transport characteristics of isotopically enriched Si-28 and will serve as a benchmark for the classical transport of Si-28 at its current state and low temperature, epitaxially grown Si for quantum devices more generally. (C) 2019 Author(s).

}, doi = {10.1063/1.5128098}, author = {Ramanayaka, A. N. and Tang, Ke and Hagmann, J. A. and Kim, Hyun-Soo and Simons, D. S. and Richter, C. A. and Pomeroy, J. M.} } @article {ISI:000466372200007, title = {Validating and certifying stabilizer states}, journal = {Phys. Rev. A}, volume = {99}, number = {4}, year = {2019}, month = {APR 30}, pages = {042337}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We propose a measurement scheme that validates the preparation of an n-qubit stabilizer state. The scheme involves a measurement of n Pauli observables, a priori determined from the stabilizer state and which can be realized using single-qubit gates. Based on the proposed validation scheme, we derive an explicit expression for the worst-case fidelity, i.e., the minimum fidelity between the stabilizer state and any other state consistent with the measured data. We also show that the worst-case fidelity can be certified, with high probability, using O(n(2)) copies of the state.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.99.042337}, author = {Kalev, Amir and Kyrillidis, Anastasios and Linke, Norbert M.} } @article {14171, title = {Verified quantum information scrambling}, journal = {Nature}, year = {2019}, month = {03/2019}, doi = {10.1038/s41586-019-0952-6}, author = {Landsman, Kevin A. and Figgatt, Caroline and Schuster, T and Linke, Norbert M. and Yoshida, B and Yao, Norman Y. and Monroe, Christopher R.} } @article { ISI:000488514800006, title = {Weak Ergodicity Breaking and Quantum Many-Body Scars in Spin-1 XY Magnets}, journal = {Phys. Rev. Lett.}, volume = {123}, number = {14}, year = {2019}, month = {OCT 1}, pages = {147201}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study the spin-1 XY model on a hypercubic lattice in d dimensions and show that this well-known nonintegrable model hosts an extensive set of anomalous finite-energy-density eigenstates with remarkable properties. Namely, they exhibit subextensive entanglement entropy and spatiotemporal long-range order, both believed to be impossible in typical highly excited eigenstates of nonintegrable quantum many-body systems. While generic initial states are expected to thermalize, we show analytically that the eigenstates we construct lead to weak crgodicity breaking in the form of persistent oscillations of local observablcs following certain quantum quenches-in other words, these eigenstates provide an archetypal example of so-called quantum many-body scars. This Letter opens the door to the analytical study of the microscopic origin, dynamical signatures, and stability of such phenomena.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.123.147201}, author = {Schecter, Michael and Iadecola, Thomas} } @article { ISI:000490121400025, title = {Weakly bound molecules as sensors of new gravity like forces}, journal = {Sci Rep}, volume = {9}, year = {2019}, month = {OCT 15}, pages = {14807}, publisher = {NATURE PUBLISHING GROUP}, type = {Article}, abstract = {Several extensions to the Standard Model of particle physics, including light dark matter candidates and unification theories predict deviations from Newton{\textquoteright}s law of gravitation. For macroscopic distances, the inverse-square law of gravitation is well confirmed by astrophysical observations and laboratory experiments. At micrometer and shorter length scales, however, even the state-of-the-art constraints on deviations from gravitational interaction, whether provided by neutron scattering or precise measurements of forces between macroscopic bodies, are currently many orders of magnitude larger than gravity itself. Here we show that precision spectroscopy of weakly bound molecules can be used to constrain non-Newtonian interactions between atoms. A proof-of-principle demonstration using recent data from photoassociation spectroscopy of weakly bound Yb-2 molecules yields constraints on these new interactions that are already close to state-of-the-art neutron scattering experiments. At the same time, with the development of the recently proposed optical molecular clocks, the neutron scattering constraints could be surpassed by at least two orders of magnitude.}, issn = {2045-2322}, doi = {10.1038/s41598-019-51346-y}, author = {Borkowski, Mateusz and Buchachenko, Alexei A. and Ciurylo, Roman and Julienne, Paul S. and Yamada, Hirotaka and Kikuchi, Yuu and Takasu, Yosuke and Takahashi, Yoshiro} } @article {ISI:000457732400002, title = {Wiedemann-Franz law and Fermi liquids}, journal = {Phys. Rev. B}, volume = {99}, number = {8}, year = {2019}, month = {FEB 4}, pages = {085104}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We consider in depth the applicability of the Wiedemann-Franz (WF) law, namely that the electronic thermal conductivity (K) is proportional to the product of the absolute temperature (T) and the electrical conductivity (a) in a metal with the constant of proportionality, the so-called Lorenz number L-0, being a materials-independent universal constant in all systems obeying the Fermi liquid (FL) paradigm. It has been often stated that the validity (invalidity) of the WF law is the hallmark of an FL {[}non-Fermi liquid (NFL)]. We consider, both in two (2D) and three (3D) dimensions, a system of conduction electrons at a finite temperature T coupled to a bath of acoustic phonons and quenched impurities, ignoring effects of electron-electron interactions. We find that the WF law is violated arbitrarily strongly with the effective Lorenz number vanishing at low temperatures as long as phonon scattering is stronger than impurity scattering. This happens both in 2D and in 3D for T < T-BG, where T-BG is the Bloch-Griineisen temperature of the system. In the absence of phonon scattering (or equivalently, when impurity scattering is much stronger than the phonon scattering), however, the WF law is restored at low temperatures even if the impurity scattering is mostly small angle forward scattering. Thus, strictly at T = 0 the WF law is always valid in a FL in the presence of infinitesimal impurity scattering. For strong phonon scattering, the WF law is restored for T > T-BG (or the Debye temperature T-D, whichever is lower) as in usual metals. At very high temperatures, thermal smearing of the Fermi surface causes the effective Lorenz number to go below L-0, manifesting a quantitative deviation from the WF law. Our paper establishes definitively that the uncritical association of an NFL behavior with the failure of the WF law is incorrect.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.085104}, author = {Lavasani, Ali and Bulmash, Daniel and S. Das Sarma} } @article { ISI:000433962700091, title = {A 3D-printed alkali metal dispenser}, journal = {REVIEW OF SCIENTIFIC INSTRUMENTS}, volume = {89}, number = {5}, year = {2018}, month = {MAY}, pages = {056101}, issn = {0034-6748}, doi = {10.1063/1.5023906}, author = {Norrgard, E. B. and Barker, D. S. and Fedchak, J. A. and Klimov, N. and Scherschligt, J. and Eckel, S.} } @article {ISI:000423432700002, title = {Absence of thermalization in finite isolated interacting Floquet systems}, journal = {PHYSICAL REVIEW B}, volume = {97}, number = {1}, year = {2018}, month = {JAN 29}, pages = {014311}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Conventional wisdom suggests that the long-time behavior of isolated interacting periodically driven (Floquet) systems is a featureless maximal-entropy state characterized by an infinite temperature. Efforts to thwart this uninteresting fixed point include adding sufficient disorder to realize a Floquet many-body localized phase or working in a narrow region of drive frequencies to achieve glassy nonthermal behavior at long time. Here we show that in clean systems the Floquet eigenstates can exhibit nonthermal behavior due to finite system size. We consider a one-dimensional system of spinless fermions with nearest-neighbor interactions where the interaction term is driven. Interestingly, even with no static component of the interaction, the quasienergy spectrum contains gaps and a significant fraction of the Floquet eigenstates, at all quasienergies, have nonthermal average doublon densities. We show that this nonthermal behavior arises due to emergent integrability at large interaction strength and discuss how the integrability breaks down with power-law dependence on system size.}, \%\%Address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, issn = {2469-9950}, doi = {10.1103/PhysRevB.97.014311}, author = {Seetharam, Karthik and Titum, Paraj and Kolodrubetz, Michael and Refael, Gil} } @article { ISI:000454636100002, title = {Alkaline-Earth Atoms in Optical Tweezers}, journal = {PHYSICAL REVIEW X}, volume = {8}, number = {4}, year = {2018}, month = {DEC 28}, pages = {041055}, abstract = {We demonstrate single-shot imaging and narrow-line cooling of individual alkaline-earth atoms in optical tweezers; specifically, strontium trapped in 515.2-nm light. Our approach enables high-fidelity detection of single atoms by imaging photons from the broad singlet transition while cooling on the narrow intercombination line, and we extend this technique to highly uniform two-dimensional tweezer arrays with 121 sites. Cooling during imaging is based on a previously unobserved narrow-line Sisyphus mechanism, which we predict to be applicable in a wide variety of experimental situations. Further, we demonstrate optically resolved sideband cooling of a single atom to near the motional ground state of a tweezer, which is tuned to a magic-trapping configuration achieved by elliptical polarization. Finally, we present calculations, in agreement with our experimental results, that predict a linear-polarization and polarization-independent magic crossing at 520(2) nm and 500.65(50) nm, respectively. Our results pave the way for a wide range of novel experimental avenues based on individually controlled alkaline-earth atoms in tweezers-from fundamental experiments in atomic physics to quantum computing, simulation, and metrology.}, keywords = {Atomic and molecular physics, Quantum Information, Quantum Physics}, issn = {2160-3308}, doi = {10.1103/PhysRevX.8.041055}, author = {Cooper, Alexandre and Covey, Jacob P. and Madjarov, Ivaylo S. and Porsev, Sergey G. and Safronova, Marianna S. and Endres, Manuel} } @article { ISI:000442061000007, title = {Analogue stochastic gravity in strongly-interacting Bose-Einstein condensates}, journal = {ANNALS OF PHYSICS}, volume = {395}, year = {2018}, month = {AUG}, pages = {84-111}, keywords = {Collective modes, General relativity, Quantum fluids, Stochastic dynamics}, issn = {0003-4916}, doi = {10.1016/j.aop.2018.05.009}, author = {Keser, Aydin Cem and Galitski, Victor} } @article { ISI:000435333100006, title = {Anisotropic exciton transport in transition-metal dichalcogenides}, journal = {PHYSICAL REVIEW B}, volume = {97}, number = {24}, year = {2018}, month = {JUN 14}, pages = {245411}, issn = {2469-9950}, doi = {10.1103/PhysRevB.97.245411}, author = {Ghazaryan, Areg and Hafezi, Mohammad and Ghaemi, Pouyan} } @article { ISI:000452687700006, title = {Anomalous normal-state resistivity in superconducting La2-xCexCuO4: Fermi liquid or strange metal?}, journal = {PHYSICAL REVIEW B}, volume = {98}, number = {22}, year = {2018}, month = {DEC 10}, pages = {224503}, abstract = {We present experimental results for the in-plane resistivity of the electron-doped cuprate superconductor La2-xCexCuO4 above its transition temperature T-c as a function of Ce doping x and temperature. For the doping x between 0.11 and 0.17, where T-c varies from 30 K (x = 0.11) to 5 K (x = 0.17), we find that the resistivity shows a T-2 behavior for all values of doping over the measurement range from 70 to 250 K. The coefficient of the T-2 resistivity term decreases with increasing x following the trend in We analyze our data theoretically and posit that n-type cuprates are better thought of as strange metals. Although the quadratic temperature dependence appears to be in naive agreement with the Fermi-liquid (FL) expectations, the facts that the measured resistivity is large and approximate T-2 scattering dominates the resistivity even up to 400 K argue against a standard normal-metal FL picture being applicable. We discuss possible origins of the strange-metal behavior.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.98.224503}, author = {Sarkar, Tarapada and Greene, Richard L. and S. Das Sarma} } @article {10551, title = {Asymmetric Particle Transport and Light-Cone Dynamics Induced by Anyonic Statistics}, journal = {Phys. Rev. Lett.}, volume = {121}, year = {2018}, month = {Dec}, pages = {250404}, doi = {10.1103/PhysRevLett.121.250404}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.121.250404}, author = {Liu, Fangli and Garrison, James R. and Deng, Dong-Ling and Gong, Zhe-Xuan and Gorshkov, Alexey V.} } @article { ISI:000453488800011, title = {Atom-by-Atom Construction of a Cyclic Artificial Molecule in Silicon}, journal = {NANO LETTERS}, volume = {18}, number = {12}, year = {2018}, month = {DEC}, pages = {7502-7508}, abstract = {Hydrogen atoms on a silicon surface, H-Si (100), behave as a resist that can be patterned with perfect atomic precision using a scanning tunneling microscope. When a hydrogen atom is removed in this manner, the underlying silicon presents a chemically active site, commonly referred to as a dangling bond. It has been predicted that individual dangling bonds function as artificial atoms, which, if grouped together, can form designer molecules on the H-Si (100) surface. Here, we present an artificial ring structure molecule spanning three dimer rows, constructed from dangling bonds, and verified by spectroscopic measurement of its molecular orbitals. We found that removing 8 hydrogen atoms resulted in a molecular analog to 1,4-disilylene-hexasilabenzene (Si8H8). Scanning tunneling spectroscopic measurements reveal molecular pi and pi{*} orbitals that agree with those expected for the same molecule in a vacuum; this is validated by density functional theory calculations of the dangling bond system on a silicon slab that show direct links both to the experimental results and to calculations for the isolated molecule. We believe the unique electronic structure of artificial molecules constructed in this manner can be engineered to enable future molecule-based electronics, surface catalytic functionality, and templating for subsequent site selective deposition.}, keywords = {Artificial molecule, dangling bonds, feedback-controlled lithography, molecular orbitals}, issn = {1530-6984}, doi = {10.1021/acs.nanolett.8b02919}, author = {Wyrick, Jonathan and Wang, Xiqiao and Namboodiri, Pradeep and Schmucker, Scott W. and Kashid, Ranjit V. and Silver, Richard M.} } @article { ISI:000423426200008, title = {Atomic properties of actinide ions with particle-hole configurations}, journal = {PHYSICAL REVIEW A}, volume = {97}, number = {1}, year = {2018}, month = {JAN 25}, pages = {012511}, issn = {2469-9926}, doi = {10.1103/PhysRevA.97.012511}, author = {Safronova, M. S. and Safronova, U. I. and Kozlov, M. G.} } @article { ISI:000428774000001, title = {Attosecond transient absorption spectrum of argon at the L-2,L-3 edge}, journal = {PHYSICAL REVIEW A}, volume = {97}, number = {3}, year = {2018}, month = {MAR 30}, pages = {031407}, issn = {2469-9926}, doi = {10.1103/PhysRevA.97.031407}, author = {Chew, Andrew and Douguet, Nicolas and Cariker, Coleman and Li, Jie and Lindroth, Eva and Ren, Xiaoming and Yin, Yanchun and Argenti, Luca and Hill, III, Wendell T. and Chang, Zenghu} } @article { ISI:000433912300001, title = {An autonomous single-piston engine with a quantum rotor}, journal = {QUANTUM SCIENCE AND TECHNOLOGY}, volume = {3}, number = {3}, year = {2018}, month = {JUL}, pages = {UNSP 035008}, keywords = {autonomous heat engine, quantum thermodynamics, rotor heat engine}, issn = {2058-9565}, doi = {10.1088/2058-9565/aac40d}, author = {Roulet, Alexandre and Nimmrichter, Stefan and Taylor, Jacob M.} } @article { ISI:000450960700005, title = {Bell monogamy relations in arbitrary qubit networks}, journal = {PHYSICAL REVIEW A}, volume = {98}, number = {5}, year = {2018}, month = {NOV 20}, pages = {052325}, issn = {2469-9926}, doi = {10.1103/PhysRevA.98.052325}, author = {Tran, M. C. and Ramanathan, R. and McKague, M. and Kaszlikowski, D. and Paterek, T.} } @article {ISI:000431374900011, title = {Beyond triplet: Unconventional superconductivity in a spin-3/2 topological semimetal}, journal = {SCIENCE ADVANCES}, volume = {4}, number = {4}, year = {2018}, month = {APR}, pages = {eaao4513}, publisher = {AMER ASSOC ADVANCEMENT SCIENCE}, type = {Article}, abstract = {In all known fermionic superfluids, Cooper pairs are composed of spin-1/2 quasi-particles that pair to formeither spinsinglet or spin-triplet bound states. The {\textquoteleft}{\textquoteleft}spin{{\textquoteright}{\textquoteright}} of a Bloch electron, however, is fixed by the symmetries of the crystal and the atomic orbitals from which it is derived and, in some cases, can behave as if it were a spin-3/2 particle. The superconducting state of such a system allows pairing beyond spin-triplet, with higher spin quasi-particles combining to formquintet or septet pairs. We report evidence of unconventional superconductivity emerging from a spin-3/2 quasi-particle electronic structure in the half-Heusler semimetal YPtBi, a low-carrier density noncentrosymmetric cubic material with a high symmetry that preserves the p-like j = 3/2 manifold in the Bi-based Gamma(8) band in the presence of strong spin-orbit coupling. With a striking linear temperature dependence of the London penetration depth, the existence of line nodes in the superconducting order parameter Delta is directly explained by a mixed-parity Cooper pairing model with high total angular momentum, consistent with a high-spin fermionic superfluid state. We propose a k.p model of the j = 3/2 fermions to explain how a dominant J = 3 septet pairing state is the simplest solution that naturally produces nodes in the mixed even-odd parity gap. Together with the underlying topologically nontrivial band structure, the unconventional pairing in this system represents a truly novel form of superfluidity that has strong potential for leading the development of a new series of topological superconductors.

}, issn = {2375-2548}, doi = {10.1126/sciadv.aao4513}, author = {Kim, Hyunsoo and Wang, Kefeng and Nakajima, Yasuyuki and Hu, Rongwei and Ziemak, Steven and Syers, Paul and Wang, Limin and Hodovanets, Halyna and Denlinger, Jonathan D. and Brydon, Philip M. R. and Agterberg, Daniel F. and Tanatar, Makariy A. and Prozorov, Ruslan and Paglione, Johnpierre} } @article { ISI:000419615700007, title = {Building topological quantum circuits: Majorana nanowire junctions}, journal = {PHYSICAL REVIEW B}, volume = {97}, number = {4}, year = {2018}, month = {JAN 9}, pages = {045410}, issn = {2469-9950}, doi = {10.1103/PhysRevB.97.045410}, author = {Stanescu, Tudor D. and S. Das Sarma} } @article { ISI:000433001000002, title = {Cavity-Enhanced Optical Readout of a Single Solid-State Spin}, journal = {PHYSICAL REVIEW APPLIED}, volume = {9}, number = {5}, year = {2018}, month = {MAY 9}, pages = {054013}, issn = {2331-7019}, doi = {10.1103/PhysRevApplied.9.054013}, author = {Sun, Shuo and Kim, Hyochul and Solomon, Glenn S. and Waks, Edo} } @article { ISI:000444740400001, title = {Challenges to miniaturizing cold atom technology for deployable vacuum metrology}, journal = {METROLOGIA}, volume = {55}, number = {5}, year = {2018}, month = {OCT}, pages = {S182-S193}, keywords = {cold atom sensing, quantum-SI, vacuum metrology}, issn = {0026-1394}, doi = {10.1088/1681-7575/aadbe4}, author = {Eckel, Stephen and Barker, Daniel S. and Fedchak, James A. and Klimov, Nikolai N. and Norrgard, Eric and Scherschligt, Julia and Makrides, Constantinos and Tiesinga, Eite} } @article { ISI:000452326000001, title = {Chiral anomaly without Landau levels: From the quantum to the classical regime}, journal = {PHYSICAL REVIEW B}, volume = {98}, number = {24}, year = {2018}, month = {DEC 6}, pages = {245109}, abstract = {We study the chiral anomaly in disordered Weyl semimetals, where the broken translational symmetry prevents the direct application of Nielsen and Ninomiya{\textquoteright}s mechanism and disorder is strong enough that quantum effects are important. In the weak disorder regime, there exist rare regions of the random potential where the disorder strength is locally strong, which gives rise to quasilocalized resonances and their effect on the chiral anomaly is unknown. We numerically show that these resonant states do not affect the chiral anomaly only in the case of a single Weyl node. At energies away from the Weyl point, or with strong disorder where one is deep in the diffusive regime, the chiral Landau level itself is not well defined and the semiclassical treatment is not justified. In this limit, we analytically use the supersymmetry method and find that the Chern-Simons term in the effective action which is not present in nontopological systems gives rise to a nonzero average level velocity which implies chiral charge pumping. We numerically establish that the nonzero average level velocity serves as an indicator of the chiral anomaly in the diffusive limit.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.98.245109}, author = {Lee, Junhyun and Pixley, J. H. and Sau, Jay D.} } @article { ISI:000445336700001, title = {Chiral Majorana fermion modes on the surface of superconducting topological insulators}, journal = {EPL}, volume = {123}, number = {4}, year = {2018}, month = {AUG}, pages = {47005}, issn = {0295-5075}, doi = {10.1209/0295-5075/123/47005}, author = {Chiu, Ching-Kai and Bian, Guang and Zheng, Hao and Yin, Jia-Xin and Zhang, Songtian S. and Sanchez, D. S. and Belopolski, I and Xu, Su-Yang and Hasan, M. Zahid} } @article { ISI:000423228300001, title = {Chiral spin currents in a trapped-ion quantum simulator using Floquet engineering}, journal = {PHYSICAL REVIEW A}, volume = {97}, number = {1}, year = {2018}, month = {JAN 19}, pages = {010302}, issn = {2469-9926}, doi = {10.1103/PhysRevA.97.010302}, author = {Grass, Tobias and Celi, Alessio and Pagano, Guido and Lewenstein, Maciej} } @article { ISI:000452324400004, title = {Chiral supercurrent through a quantum Hall weak link}, journal = {PHYSICAL REVIEW B}, volume = {98}, number = {21}, year = {2018}, month = {DEC 6}, pages = {214504}, abstract = {We use an effective model to calculate properties of the supercurrent carried by chiral edge states of a quantum Hall weak link. This {\textquoteleft}{\textquoteleft}chiral{{\textquoteright}{\textquoteright}} supercurrent is qualitatively distinct from the usual Josephson supercurrent in that it cannot be mediated by a single edge alone, i.e., both right- and left-going edges are needed. Moreover, the chiral supercurrent was previously shown to obey an unusual current-phase relation with period 2 phi(0) = h/e, which is twice the period of conventional Josephson junctions. We show that the {\textquoteleft}{\textquoteleft}chiral{{\textquoteright}{\textquoteright}} nature of this supercurrent is sharply defined, and is robust to interactions to infinite order in perturbation theory. We compare our results with recent experimental findings {[}Amet et al., Science 352 966 (2016)] and find that quantitative agreement in the magnitude of the supercurrent can be attained by making reasonable but critical assumptions about the superconductor quantum Hall interface.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.98.214504}, author = {Alavirad, Yahya and Lee, Junhyun and Lin, Ze-Xun and Sau, Jay D.} } @article { ISI:000441668600006, title = {Clock-related properties of Lu+}, journal = {PHYSICAL REVIEW A}, volume = {98}, number = {2}, year = {2018}, month = {AUG 14}, pages = {022509}, issn = {2469-9926}, doi = {10.1103/PhysRevA.98.022509}, author = {Porsev, S. G. and Safronova, U. I. and Safronova, M. S.} } @article { ISI:000428617600038, title = {A coherent spin-photon interface in silicon}, journal = {NATURE}, volume = {555}, number = {7698}, year = {2018}, month = {MAR 29}, pages = {599+}, issn = {0028-0836}, doi = {10.1038/nature25769}, author = {Mi, X. and Benito, M. and Putz, S. and Zajac, D. M. and Taylor, J. M. and Burkard, Guido and Petta, J. R.} } @article { ISI:000448933900004, title = {Collective Effects in Casimir-Polder Forces}, journal = {PHYSICAL REVIEW LETTERS}, volume = {121}, number = {18}, year = {2018}, month = {NOV 1}, pages = {183605}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.121.183605}, author = {Sinha, Kanupriya and Venkatesh, B. Prasanna and Meystre, Pierre} } @article { ISI:000423428400002, title = {Conductance interference in a superconducting Coulomb blockaded Majorana ring}, journal = {PHYSICAL REVIEW B}, volume = {97}, number = {3}, year = {2018}, month = {JAN 26}, pages = {035310}, issn = {2469-9950}, doi = {10.1103/PhysRevB.97.035310}, author = {Chiu, Ching-Kai and Sau, Jay D. and S. Das Sarma} } @article { ISI:000449292600001, title = {Configuration-controlled many-body localization and the mobility emulsion}, journal = {PHYSICAL REVIEW B}, volume = {98}, number = {17}, year = {2018}, month = {NOV 2}, pages = {174201}, issn = {2469-9950}, doi = {10.1103/PhysRevB.98.174201}, author = {Schecter, Michael and Iadecola, Thomas and S. Das Sarma} } @article { ISI:000452675100001, title = {Confocal laser scanning microscopy for rapid optical characterization of graphene}, journal = {COMMUNICATIONS PHYSICS}, volume = {1}, year = {2018}, month = {NOV 20}, pages = {83}, issn = {2399-3650}, doi = {10.1038/s42005-018-0084-6}, author = {Panchal, Vishal and Yang, Yanfei and Cheng, Guangjun and Hu, Jiuning and Kruskopf, Mattias and Liu, I, Chieh- and Rigosi, Albert F. and Melios, Christos and Walker, Angela R. Hight and Newell, David B. and Kazakova, Olga and Elmquist, Randolph E.} } @article { ISI:000423614600001, title = {Controlling the layer localization of gapless states in bilayer graphene with a gate voltage}, journal = {2D MATERIALS}, volume = {5}, number = {2}, year = {2018}, month = {APR}, pages = {025006}, keywords = {bilayer graphene, graphene, topologically protected states}, issn = {2053-1583}, doi = {10.1088/2053-1583/aaa490}, author = {Jaskolski, W. and Pelc, M. and Bryant, Garnett W. and Chico, Leonor and Ayuela, A.} } @article { ISI:000432031700004, title = {Cooper pair induced frustration and nematicity of two-dimensional magnetic adatom lattices}, journal = {PHYSICAL REVIEW B}, volume = {97}, number = {17}, year = {2018}, month = {MAY 10}, pages = {174412}, issn = {2469-9950}, doi = {10.1103/PhysRevB.97.174412}, author = {Schecter, Michael and Syljuasen, Olav F. and Paaske, Jens} } @article { ISI:000449713800005, title = {Coupling quantum emitters in WSe2 monolayers to a metal-insulator-metal waveguide}, journal = {APPLIED PHYSICS LETTERS}, volume = {113}, number = {19}, year = {2018}, month = {NOV 5}, pages = {191105}, issn = {0003-6951}, doi = {10.1063/1.5045727}, author = {Dutta, Subhojit and Cai, Tao and Buyukkaya, Mustafa Atabey and Barik, Sabyasachi and Aghaeimeibodi, Shahriar and Waks, Edo} } @conference { ISI:000450863900003, title = {Coupling single defects in 2D semiconductor to a silver nanowire}, booktitle = {2D PHOTONIC MATERIALS AND DEVICES}, series = {Proceedings of SPIE}, volume = {10534}, year = {2018}, note = {Conference on 2D Photonic Materials and Devices, San Francisco, CA, JAN 29-31, 2018}, pages = {105340F}, keywords = {2D semiconductors, defect emission, silver nanowire, Surface plasmon polaritons, transition metal dichalcogenide, tungsten diselenide}, isbn = {978-1-5106-1554-0; 978-1-5106-1553-3}, issn = {0277-786X}, doi = {10.1117/12.2285431}, author = {Cai, Tao and Dutta, Subhojit and Aghaeimeibodi, Shahriar and Yang, Zhili and Nah, Sanghee and Fourkas, John T. and Waks, Edo}, editor = {Majumdar, A and Xu, X and Hendrickson, JR} } @article { ISI:000423433700007, title = {Crosstalk error correction through dynamical decoupling of single-qubit gates in capacitively coupled singlet-triplet semiconductor spin qubits}, journal = {PHYSICAL REVIEW B}, volume = {97}, number = {4}, year = {2018}, month = {JAN 29}, pages = {045431}, issn = {2469-9950}, doi = {10.1103/PhysRevB.97.045431}, author = {Buterakos, Donovan and Throckmorton, Robert E. and S. Das Sarma} } @article {9151, title = {Dark State Optical Lattice with a Subwavelength Spatial Structure}, journal = {Phys. Rev. Lett.}, volume = {120}, year = {2018}, month = {Feb}, pages = {083601}, doi = {10.1103/PhysRevLett.120.083601}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.120.083601}, author = {Wang, Y. and Subhankar, S. and Bienias, P and {\L}{\k a}cki, M. and Tsui, T-C. and Baranov, M. A. and Gorshkov, A. V. and Zoller, P. and Porto, J. V. and Rolston, S. L.} } @article { ISI:000439334800001, title = {Demonstration of a Bayesian quantum game on an ion-trap quantum computer}, journal = {QUANTUM SCIENCE AND TECHNOLOGY}, volume = {3}, number = {4}, year = {2018}, month = {OCT}, pages = {UNSP 045002}, keywords = {ion traps, quantum computation, quantum games}, issn = {2058-9565}, doi = {10.1088/2058-9565/aacf0e}, author = {Solmeyer, Neal and Linke, Norbert M. and Figgatt, Caroline and Landsman, Kevin A. and Balu, Radhakrishnan and Siopsis, George and Monroe, C.} } @article { ISI:000428966400004, title = {Demonstration of a Sensitive Method to Measure Nuclear-Spin-Dependent Parity Violation}, journal = {PHYSICAL REVIEW LETTERS}, volume = {120}, number = {14}, year = {2018}, month = {APR 2}, pages = {142501}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.120.142501}, author = {Altuntas, Emine and Ammon, Jeffrey and Cahn, Sidney B. and DeMille, David} } @article { ISI:000429937300002, title = {Demonstration of Protection of a Superconducting Qubit from Energy Decay}, journal = {PHYSICAL REVIEW LETTERS}, volume = {120}, number = {15}, year = {2018}, month = {APR 13}, pages = {150503}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.120.150503}, author = {Lin, Yen-Hsiang and Nguyen, Long B. and Grabon, Nicholas and San Miguel, Jonathan and Pankratova, Natalia and Manucharyan, Vladimir E.} } @article { ISI:000443094300002, title = {Diluted magnetic Dirac-Weyl materials: Susceptibility and ferromagnetism in three-dimensional chiral gapless semimetals}, journal = {PHYSICAL REVIEW B}, volume = {98}, number = {6}, year = {2018}, month = {AUG 29}, pages = {064425}, issn = {2469-9950}, doi = {10.1103/PhysRevB.98.064425}, author = {Park, Sanghyun and Min, Hongki and Hwang, E. H. and S. Das Sarma} } @article { ISI:000447621900002, title = {Dimensionally mixed coupled collective modes}, journal = {PHYSICAL REVIEW B}, volume = {98}, number = {16}, year = {2018}, month = {OCT 18}, pages = {161304}, issn = {2469-9950}, doi = {10.1103/PhysRevB.98.161304}, author = {Hwang, E. H. and Hu, Ben Yu-Kuang and S. Das Sarma} } @article {ISI:000427010500002, title = {Disorder-induced half-integer quantized conductance plateau in quantum anomalous Hall insulator-superconductor structures}, journal = {PHYSICAL REVIEW B}, volume = {97}, number = {10}, year = {2018}, month = {MAR 9}, pages = {100501}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {A weak superconducting proximity effect in the vicinity of the topological transition of a quantum anomalous Hall system has been proposed as a venue to realize a topological superconductor (TSC) with chiral Majorana edge modes (CMEMs). A recent experiment {[}Science 357, 294 (2017)] claimed to have observed such CMEMs in the form of a half-integer quantized conductance plateau in the two-terminal transport measurement of a quantum anomalous Hall-superconductor junction. Although the presence of a superconducting proximity effect generically splits the quantum Hall transition into two phase transitions with a gapped TSC in between, in this Rapid Communication we propose that a nearly flat conductance plateau, similar to that expected from CMEMs, can also arise from the percolation of quantum Hall edges well before the onset of the TSC or at temperatures much above the TSC gap. Our Rapid Communication, therefore, suggests that, in order to confirm the TSC, it is necessary to supplement the observation of the half-quantized conductance plateau with a hard superconducting gap (which is unlikely for a disordered system) from the conductance measurements or the heat transport measurement of the transport gap. Alternatively, the half-quantized thermal conductance would also serve as a smoking-gun signature of the TSC.}, \%\%Address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, issn = {2469-9950}, doi = {10.1103/PhysRevB.97.100501}, author = {Huang, Yingyi and Setiawan, F. and Sau, Jay D.} } @article { ISI:000444557300003, title = {Dissipation-enabled fractional Josephson effect}, journal = {PHYSICAL REVIEW B}, volume = {98}, number = {12}, year = {2018}, month = {SEP 12}, pages = {125124}, issn = {2469-9950}, doi = {10.1103/PhysRevB.98.125124}, author = {Sticlet, Doru and Sau, Jay D. and Akhmerov, Anton} } @article {ISI:000426249900005, title = {Dissipation-induced dipole blockade and antiblockade in driven Rydberg systems}, journal = {PHYSICAL REVIEW A}, volume = {97}, number = {2}, year = {2018}, month = {FEB 28}, pages = {023424}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study theoretically and experimentally the competing blockade and antiblockade effects induced by spontaneously generated contaminant Rydberg atoms in driven Rydberg systems. These contaminant atoms provide a source of strong dipole-dipole interactions and play a crucial role in the system{\textquoteright}s behavior. We study this problem theoretically using two different approaches. The first is a cumulant expansion approximation, in which we ignore third-order and higher connected correlations. Using this approach for the case of resonant drive, a many-body blockade radius picture arises, and we find qualitative agreement with previous experimental results. We further predict that as the atomic density is increased, the Rydberg population{\textquoteright}s dependence on Rabi frequency will transition from quadratic to linear dependence at lower Rabi frequencies. We study this behavior experimentally by observing this crossover at two different atomic densities. We confirm that the larger density system has a smaller crossover Rabi frequency than the smaller density system. The second theoretical approach is a set of phenomenological inhomogeneous rate equations. We compare the results of our rate-equation model to the experimental observations {[}E. A. Goldschmidt et al., Phys. Rev. Lett. 116, 113001 (2016)] and find that these rate equations provide quantitatively good scaling behavior of the steady-state Rydberg population for both resonant and off-resonant drives.}, \%\%Address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, issn = {2469-9926}, doi = {10.1103/PhysRevA.97.023424}, author = {Young, Jeremy T. and Boulier, Thomas and Magnan, Eric and Goldschmidt, Elizabeth A. and Wilson, Ryan M. and Rolston, Steven L. and Porto, James V. and Gorshkov, Alexey V.} } @article { ISI:000434209100002, title = {Distinguishing topological Majorana bound states from trivial Andreev bound states: Proposed tests through differential tunneling conductance spectroscopy}, journal = {PHYSICAL REVIEW B}, volume = {97}, number = {21}, year = {2018}, month = {JUN 5}, pages = {214502}, issn = {2469-9950}, doi = {10.1103/PhysRevB.97.214502}, author = {Liu, Chun-Xiao and Sau, Jay D. and S. Das Sarma} } @article { ISI:000439744700003, title = {Distributed Quantum Metrology with Linear Networks and Separable Inputs}, journal = {PHYSICAL REVIEW LETTERS}, volume = {121}, number = {4}, year = {2018}, month = {JUL 25}, pages = {043604}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.121.043604}, author = {Ge, Wenchao and Jacobs, Kurt and Eldredge, Zachary and Gorshkov, V, Alexey and Foss-Feig, Michael} } @article { ISI:000432971400001, title = {Does a Single Eigenstate Encode the Full Hamiltonian?}, journal = {PHYSICAL REVIEW X}, volume = {8}, number = {2}, year = {2018}, month = {APR 30}, pages = {021026}, issn = {2160-3308}, doi = {10.1103/PhysRevX.8.021026}, author = {Garrison, James R. and Grover, Tarun} } @article { ISI:000419476900017, title = {Dressed infrared quantum information}, journal = {PHYSICAL REVIEW D}, volume = {97}, number = {2}, year = {2018}, month = {JAN 8}, pages = {025007}, issn = {2470-0010}, doi = {10.1103/PhysRevD.97.025007}, author = {Carney, Daniel and Chaurette, Laurent and Neuenfeld, Dominik and Semenoff, Gordon Walter} } @article {10101, title = {Dynamical Phase Transitions in Sampling Complexity}, journal = {Phys. Rev. Lett.}, volume = {121}, year = {2018}, month = {Jul}, pages = {030501}, doi = {10.1103/PhysRevLett.121.030501}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.121.030501}, author = {Deshpande, Abhinav and Fefferman, Bill and Tran, Minh C. and Foss-Feig, Michael and Gorshkov, Alexey V.} } @article {10476, title = {Dynamo Effect and Turbulence in Hydrodynamic Weyl Metals}, journal = {Phys. Rev. Lett.}, volume = {121}, year = {2018}, month = {Oct}, pages = {176603}, doi = {10.1103/PhysRevLett.121.176603}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.121.176603}, author = {Galitski, Victor and Kargarian, Mehdi and Syzranov, Sergey} } @article { ISI:000447148100009, title = {Effect of device design on charge offset drift in Si/SiO2 single electron devices}, journal = {JOURNAL OF APPLIED PHYSICS}, volume = {124}, number = {14}, year = {2018}, month = {OCT 14}, pages = {144302}, issn = {0021-8979}, doi = {10.1063/1.5048013}, author = {Hu, Binhui and Ochoa, Erick D. and Sanchez, Daniel and Perron, Justin K. and Zimmerman, Neil M. and Stewart, Jr., M. D.} } @article { ISI:000437843700001, title = {Effective renormalized multi-body interactions of harmonically confined ultracold neutral bosons (vol 14, 053037, 2012)}, journal = {NEW JOURNAL OF PHYSICS}, volume = {20}, year = {2018}, month = {JUL 6}, pages = {079501}, issn = {1367-2630}, doi = {10.1088/1367-2630/aacf78}, author = {Johnson, P. R. and Blume, D. and Yin, X. Y. and Flynn, W. F. and Tiesinga, E.} } @article { ISI:000439543800001, title = {Effective theory approach to the Schrodinger-Poisson problem in semiconductor Majorana devices}, journal = {PHYSICAL REVIEW B}, volume = {98}, number = {3}, year = {2018}, month = {JUL 24}, pages = {035428}, issn = {2469-9950}, doi = {10.1103/PhysRevB.98.035428}, author = {Woods, Benjamin D. and Stanescu, Tudor D. and S. Das Sarma} } @article {ISI:000430601100005, title = {Effects of resonant-laser excitation on the emission properties in a single quantum dot}, journal = {OPTICA}, volume = {5}, number = {4}, year = {2018}, month = {APR 20}, pages = {354-359}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {While many solid-state emitters can be optically excited non-resonantly, resonant excitation is necessary for many quantum information protocols as it often maximizes the non-classicality of the emitted light. Here, we study the resonance fluorescence in a solid-state system-a quantum dot-with the addition of weak, non-resonant light. In the inelastic scattering regime, changes in the resonance fluorescence intensity and linewidth are linked to both the non-resonant and resonant laser powers. Details of the intensity change indicate that charge-carrier loss from the quantum dot is resonant laser. As we enter the Mollow triplet regime, this resonant laser loss term rate is approximately 1/50 ns(-1). This work further clarifies resonance fluorescence in solid-state systems and will aid in the further improvement of solid-state non-classical light sources.}, \%\%Address = {2010 MASSACHUSETTS AVE NW, WASHINGTON, DC 20036 USA}, issn = {2334-2536}, doi = {10.1364/OPTICA.5.000354}, author = {Gazzano, O. and Huber, T. and Loo, V and Polyakov, S. and Flagg, E. B. and Solomon, G. S.} } @article { ISI:000425507400010, title = {Electro-mechano-optical detection of nuclear magnetic resonance}, journal = {OPTICA}, volume = {5}, number = {2}, year = {2018}, month = {FEB 20}, pages = {152-158}, issn = {2334-2536}, doi = {10.1364/OPTICA.5.000152}, author = {Takeda, Kazuyuki and Nagasaka, Kentaro and Noguchi, Atsushi and Yamazaki, Rekishu and Nakamura, Yasunobu and Iwase, Eiji and Taylor, Jacob M. and Usami, Koji} } @article { ISI:000435442300004, title = {Electronic hydrodynamics and the breakdown of the Wiedemann-Franz and Mott laws in interacting metals}, journal = {PHYSICAL REVIEW B}, volume = {97}, number = {24}, year = {2018}, month = {JUN 18}, pages = {245128}, issn = {2469-9950}, doi = {10.1103/PhysRevB.97.245128}, author = {Lucas, Andrew and S. Das Sarma} } @article { ISI:000428501200005, title = {Electronic sound modes and plasmons in hydrodynamic two-dimensional metals}, journal = {PHYSICAL REVIEW B}, volume = {97}, number = {11}, year = {2018}, month = {MAR 28}, pages = {115449}, issn = {2469-9950}, doi = {10.1103/PhysRevB.97.115449}, author = {Lucas, Andrew and S. Das Sarma} } @article { ISI:000447310800001, title = {Electrooptomechanical Equivalent Circuits for Quantum Transduction}, journal = {PHYSICAL REVIEW APPLIED}, volume = {10}, number = {4}, year = {2018}, month = {OCT 15}, pages = {044036}, issn = {2331-7019}, doi = {10.1103/PhysRevApplied.10.044036}, author = {Zeuthen, Emil and Schliesser, Albert and Taylor, Jacob M. and Sorensen, Anders S.} } @article { ISI:000450048400053, title = {Emergence of multi-body interactions in a fermionic lattice clock}, journal = {NATURE}, volume = {563}, number = {7731}, year = {2018}, month = {NOV 15}, pages = {369+}, issn = {0028-0836}, doi = {10.1038/s41586-018-0661-6}, author = {Goban, A. and Hutson, R. B. and Marti, G. E. and Campbell, S. L. and Perlin, M. A. and Julienne, P. S. and D{\textquoteright}Incao, J. P. and Rey, A. M. and Ye, J.} } @article { ISI:000438672400001, title = {Energy-level statistics in strongly disordered systems with power-law hopping}, journal = {PHYSICAL REVIEW B}, volume = {98}, number = {1}, year = {2018}, month = {JUL 16}, pages = {014201}, issn = {2469-9950}, doi = {10.1103/PhysRevB.98.014201}, author = {Titum, Paraj and Quito, Victor L. and Syzranov, V, Sergey} } @conference { ISI:000450231900106, title = {Epitaxial Graphene for High-Current QHE Resistance Standards}, booktitle = {2018 CONFERENCE ON PRECISION ELECTROMAGNETIC MEASUREMENTS (CPEM 2018)}, year = {2018}, note = {Conference on Precision Electromagnetic Measurements (CPEM), Paris, FRANCE, JUL 08-13, 2018}, keywords = {epitaxial graphene, face-to-graphite (FTG), polymer-assisted growth (PASG), quantum resistance metrology}, isbn = {978-1-5386-0974-3}, author = {Kruskopf, Mattias and Hu, Jiuning and Wu, Bi-Yi and Yang, Yanfei and Lee, Hsin-Yen and Rigosi, Albert F. and Newell, David B. and Elmquist, Randolph E.} } @article { ISI:000439337700001, title = {Epitaxial graphene for quantum resistance metrology}, journal = {METROLOGIA}, volume = {55}, number = {4}, year = {2018}, month = {AUG}, pages = {R27-R36}, keywords = {epitaxial graphene, quantum Hall effect, quantum resistance metrology}, issn = {0026-1394}, doi = {10.1088/1681-7575/aacd23}, author = {Kruskopf, Mattias and Elmquist, Randolph E.} } @conference { ISI:000450231900084, title = {Epitaxial Graphene p-n Junctions}, booktitle = {2018 CONFERENCE ON PRECISION ELECTROMAGNETIC MEASUREMENTS (CPEM 2018)}, year = {2018}, note = {Conference on Precision Electromagnetic Measurements (CPEM), Paris, FRANCE, JUL 08-13, 2018}, keywords = {epitaxial graphene, graphene p-n junction, quantum Hall effect, resistance standard}, isbn = {978-1-5386-0974-3}, author = {Hu, Jiuning and Kruskopf, Mattias and Yang, Yanfei and Wu, Bi-Yi and Tian, Jifa and Panna, Alireza and Rigosi, Albert F. and Lee, Hsin-Yen and Payagala, Shamith and Jones, George R. and Kraft, Marlin E. and Jarrett, Dean G. and Watanabe, Kenji and Taniguchi, Takashi and Elmquist, Randolph E. and Newell, David B.} } @article { ISI:000451073900001, title = {Equations of state from individual one-dimensional Bose gases}, journal = {NEW JOURNAL OF PHYSICS}, volume = {20}, year = {2018}, month = {NOV 23}, pages = {113032}, abstract = {We trap individual 1D Bose gases and obtain the associated equation of state by combining calibrated confining potentials with in situ density profiles. Our observations agree well with the exact Yang- Yang 1D thermodynamic solutions under the local density approximation. We find that our final 1D system undergoes inefficient evaporative cooling that decreases the absolute temperature, but monotonically reduces a degeneracy parameter.}, keywords = {atomic physics, equation of state, one-dimensonal Bose gas, quantum gases}, issn = {1367-2630}, doi = {10.1088/1367-2630/aaef9b}, author = {Salces-Carcoba, F. and Billington, C. J. and Putra, A. and Yue, Y. and Sugawa, S. and Ian B Spielman} } @article { ISI:000419616600003, title = {Equivalence principle for quantum systems: dephasing and phase shift of free-falling particles}, journal = {CLASSICAL AND QUANTUM GRAVITY}, volume = {35}, number = {3}, year = {2018}, month = {FEB 8}, pages = {035011}, keywords = {equivalence principle, free fall, gravitational phase shift, gravitational quantum physics}, issn = {0264-9381}, doi = {10.1088/1361-6382/aaa0e8}, author = {Anastopoulos, C. and Hu, B. L.} } @article { ISI:000437110200003, title = {Error correction for gate operations in systems of exchange-coupled singlet-triplet qubits in double quantum dots}, journal = {PHYSICAL REVIEW B}, volume = {98}, number = {3}, year = {2018}, month = {JUL 3}, pages = {035406}, issn = {2469-9950}, doi = {10.1103/PhysRevB.98.035406}, author = {Buterakos, Donovan and Throckmorton, Robert E. and S. Das Sarma} } @article { ISI:000433265900009, title = {Examining epitaxial graphene surface conductivity and quantum Hall device stability with Parylene passivation}, journal = {MICROELECTRONIC ENGINEERING}, volume = {194}, year = {2018}, month = {JUL 5}, pages = {51-55}, keywords = {epitaxial graphene, Parylene, quantum Hall effect, Surface conductivity, Transport mobility}, issn = {0167-9317}, doi = {10.1016/j.mee.2018.03.004}, author = {Rigosi, Albert F. and Liu, Chieh-I and Wu, Bi Yi and Lee, Hsin-Yen and Kruskopf, Mattias and Yang, Yanfei and Hill, Heather M. and Hu, Jiuning and Bittle, Emily G. and Obrzut, Jan and Walker, Angela R. Hight and Elmquist, Randolph E. and Newell, David B.} } @article { ISI:000446554000001, title = {Failure of Kohn{\textquoteright}s theorem and the apparent failure of the f-sum rule in intrinsic Dirac-Weyl materials in the presence of a filled Fermi sea}, journal = {PHYSICAL REVIEW B}, volume = {98}, number = {15}, year = {2018}, month = {OCT 5}, pages = {155112}, issn = {2469-9950}, doi = {10.1103/PhysRevB.98.155112}, author = {Throckmorton, Robert E. and S. Das Sarma} } @article { ISI:000439411700003, title = {Ferromagnetism and Wigner crystallization in kagome graphene and related structures}, journal = {PHYSICAL REVIEW B}, volume = {98}, number = {3}, year = {2018}, month = {JUL 23}, pages = {035135}, issn = {2469-9950}, doi = {10.1103/PhysRevB.98.035135}, author = {Chen, Yuanping and Xu, Shenglong and Xie, Yuee and Zhong, Chengyong and Wu, Congjun and Zhang, S. B.} } @article { ISI:000439974200006, title = {Fingerprints of Berry phases in the bulk exciton spectrum of a topological insulator}, journal = {PHYSICAL REVIEW B}, volume = {98}, number = {4}, year = {2018}, month = {JUL 27}, pages = {045430}, issn = {2469-9950}, doi = {10.1103/PhysRevB.98.045430}, author = {Allocca, Andrew A. and Efimkin, Dmitry K. and Galitski, Victor M.} } @article { ISI:000433040400001, title = {Floquet Supersymmetry}, journal = {PHYSICAL REVIEW LETTERS}, volume = {120}, number = {21}, year = {2018}, month = {MAY 24}, pages = {210603}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.120.210603}, author = {Iadecola, Thomas and Hsieh, Timothy H.} } @article { ISI:000426845500044, title = {Fractal universality in near-threshold magnetic lanthanide dimers}, journal = {SCIENCE ADVANCES}, volume = {4}, number = {2}, year = {2018}, month = {FEB}, pages = {UNSP eaap8308}, issn = {2375-2548}, doi = {10.1126/sciadv.aap8308}, author = {Makrides, Constantinos and Li, Ming and Tiesinga, Eite and Kotochigova, Svetlana} } @article { ISI:000448933900006, title = {Fractional Quantum Hall Effect at nu=2+6/13: The Parton Paradigm for the Second Landau Level}, journal = {PHYSICAL REVIEW LETTERS}, volume = {121}, number = {18}, year = {2018}, month = {NOV 1}, pages = {186601}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.121.186601}, author = {Balram, Ajit C. and Mukherjee, Sutirtha and Park, Kwon and Barkeshli, Maissam and Rudner, Mark S. and Jain, J. K.} } @article {10546, title = {Fractional Quantum Hall Phases of Bosons with Tunable Interactions: From the Laughlin Liquid to a Fractional Wigner Crystal}, journal = {Phys. Rev. Lett.}, volume = {121}, year = {2018}, month = {Dec}, pages = {253403}, doi = {10.1103/PhysRevLett.121.253403}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.121.253403}, author = {Gra{\ss}, Tobias and Bienias, Przemyslaw and Gullans, Michael J. and Lundgren, Rex and Maciejko, Joseph and Gorshkov, Alexey V.} } @article { ISI:000448756700003, title = {Generation of a Lattice of Spin-Orbit Beams via Coherent Averaging}, journal = {PHYSICAL REVIEW LETTERS}, volume = {121}, number = {18}, year = {2018}, month = {OCT 30}, pages = {183602}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.121.183602}, author = {Sarenac, D. and Cory, D. G. and Nsofini, J. and Hincks, I. and Miguel, P. and Arif, M. and Clark, Charles W. and Huber, M. G. and Pushin, D. A.} } @article { ISI:000448973100018, title = {Giant anomalous Nernst effect and quantum-critical scaling in a ferromagnetic semimetal}, journal = {NATURE PHYSICS}, volume = {14}, number = {11}, year = {2018}, month = {NOV}, pages = {1119+}, issn = {1745-2473}, doi = {10.1038/s41567-018-0225-6}, author = {Sakai, Akito and Mizuta, Yo Pierre and Nugroho, Agustinus Agung and Sihombing, Rombang and Koretsune, Takashi and Suzuki, Michi-To and Takemori, Nayuta and Ishii, Rieko and Nishio-Hamane, Daisuke and Arita, Ryotaro and Goswami, Pallab and Nakatsuji, Satoru} } @article { ISI:000441010300002, title = {Global phase diagram and momentum distribution of single-particle excitations in Kondo insulators}, journal = {PHYSICAL REVIEW B}, volume = {98}, number = {8}, year = {2018}, month = {AUG 7}, pages = {085110}, issn = {2469-9950}, doi = {10.1103/PhysRevB.98.085110}, author = {Pixley, J. H. and Yu, Rong and Paschen, Silke and Si, Qimiao} } @article { ISI:000445057800002, title = {Global Phase Diagram of a Dirty Weyl Liquid and Emergent Superuniversality}, journal = {PHYSICAL REVIEW X}, volume = {8}, number = {3}, year = {2018}, month = {SEP 19}, pages = {031076}, issn = {2160-3308}, doi = {10.1103/PhysRevX.8.031076}, author = {Roy, Bitan and Slager, Robert-Jan and Juricic, Vladimir} } @article {ISI:000428598700001, title = {Hardware-efficient fermionic simulation with a cavity-QED system}, journal = {NPJ QUANTUM INFORMATION}, volume = {4}, year = {2018}, month = {FEB 27}, pages = {16}, publisher = {NATURE PUBLISHING GROUP}, type = {Article}, abstract = {In digital quantum simulation of fermionic models with qubits, non-local maps for encoding are often encountered. Such maps require linear or logarithmic overhead in circuit depth which could render the simulation useless, for a given decoherence time. Here we show how one can use a cavity-QED system to perform digital quantum simulation of fermionic models. In particular, we show that highly nonlocal Jordan-Wigner or Bravyi-Kitaev transformations can be efficiently implemented through a hardware approach. The key idea is using ancilla cavity modes, which are dispersively coupled to a qubit string, to collectively manipulate and measure qubit states. Our scheme reduces the circuit depth in each Trotter step of the Jordan-Wigner encoding by a factor of N-2, comparing to the scheme for a device with only local connectivity, where N is the number of orbitals for a generic two-body Hamiltonian. Additional analysis for the Fermi-Hubbard model on an N x N square lattice results in a similar reduction. We also discuss a detailed implementation of our scheme with superconducting qubits and cavities.}, \%\%Address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, issn = {2056-6387}, doi = {10.1038/s41534-018-0065-3}, author = {Zhu, Guanyu and Subasi, Yigit and Whitfield, James D. and Hafezi, Mohammad} } @article { ISI:000443395600003, title = {Helical Majorana edge mode in a superconducting antiferromagnetic quantum spin Hall insulator}, journal = {PHYSICAL REVIEW B}, volume = {98}, number = {8}, year = {2018}, month = {AUG 31}, pages = {081412}, issn = {2469-9950}, doi = {10.1103/PhysRevB.98.081412}, author = {Huang, Yingyi and Chiu, Ching-Kai} } @article { ISI:000434628400002, title = {Higgs mechanism in higher-rank symmetric U(1) gauge theories}, journal = {PHYSICAL REVIEW B}, volume = {97}, number = {23}, year = {2018}, month = {JUN 8}, pages = {235112}, issn = {2469-9950}, doi = {10.1103/PhysRevB.97.235112}, author = {Bulmash, Daniel and Barkeshli, Maissam} } @inbook { ISI:000429191300003, title = {High-Dimensional Disorder-Driven Phenomena in Weyl Semimetals, Semiconductors, and Related Systems}, booktitle = {ANNUAL REVIEW OF CONDENSED MATTER PHYSICS, VOL 9}, series = {Annual Review of Condensed Matter Physics}, volume = {9}, year = {2018}, pages = {35-58}, keywords = {Dirac semimetals, disordered systems, localization, phase transitions}, issn = {1947-5454}, doi = {10.1146/annurev-conmatphys-033117-054037}, author = {Syzranov, Sergey V. and Radzihovsky, Leo}, editor = {Sachdev, S and Marchetti, MC} } @article { ISI:000425091300007, title = {High-fidelity quantum gates in Si/SiGe double quantum dots}, journal = {PHYSICAL REVIEW B}, volume = {97}, number = {8}, year = {2018}, month = {FEB 15}, pages = {085421}, issn = {2469-9950}, doi = {10.1103/PhysRevB.97.085421}, author = {Russ, Maximilian and Zajac, D. M. and Sigillito, A. J. and Borjans, F. and Taylor, J. M. and Petta, J. R. and Burkard, Guido} } @article { ISI:000451992400001, title = {Highly charged ions: Optical clocks and applications in fundamental physics}, journal = {REVIEWS OF MODERN PHYSICS}, volume = {90}, number = {4}, year = {2018}, month = {DEC 4}, pages = {045005}, abstract = {Recent developments in frequency metrology and optical clocks have been based on electronic transitions in atoms and singly charged ions as references. The control over all relevant degrees of freedom in these atoms has enabled relative frequency uncertainties at a level of 10(-18). This accomplishment not only allows for extremely accurate time and frequency measurements, but also to probe our understanding of fundamental physics, such as a possible variation of fundamental constants, a violation of the local Lorentz invariance, and the existence of forces beyond the standard model of physics. In addition, novel clocks are driving the development of sophisticated technical applications. Crucial for applications of clocks in fundamental physics are a high sensitivity to effects beyond the standard model and a small frequency uncertainty of the clock. Highly charged ions offer both. They possess optical transitions which can be extremely narrow and less sensitive to external perturbations compared to current atomic clock species. The large selection of highly charged ions offers narrow transitions that are among the most sensitive ones for the {\textquoteleft}{\textquoteleft}new physics{{\textquoteright}{\textquoteright}} effects. Recent experimental advances in trapping and sympathetic cooling of highly charged ions will in the future enable advanced quantum logic techniques for controlling motional and internal degrees of freedom and thus enable high-accuracy optical spectroscopy. Theoretical progress in calculating the properties of selected highly charged ions has allowed the evaluation of systematic shifts and the prediction of the sensitivity to the physics beyond the standard model. New theoretical challenges and opportunities emerge from relativistic, quantum electrodynamics, and nuclear-size contributions that become comparable with interelectronic correlations. This article reviews the current status of the field, addresses specific electronic configurations and systems which show the most promising properties for research, their potential limitations, and the techniques for their study.}, issn = {0034-6861}, doi = {10.1103/RevModPhys.90.045005}, author = {Kozlov, M. G. and Safronova, M. S. and Lopez-Urrutia, J. R. Crespo and Schmidt, P. O.} } @article { ISI:000425089500005, title = {High-precision measurements and theoretical calculations of indium excited-state polarizabilities}, journal = {PHYSICAL REVIEW A}, volume = {97}, number = {2}, year = {2018}, month = {FEB 15}, pages = {022507}, issn = {2469-9926}, doi = {10.1103/PhysRevA.97.022507}, author = {Vilas, N. B. and Wang, B. -Y. and Rupasinghe, P. M. and Maser, D. L. and Safronova, M. S. and Safronova, U. I. and Majumder, P. K.} } @article { ISI:000444724300005, title = {Implementing Majorana fermions in a cold-atom honeycomb lattice with textured pairings}, journal = {PHYSICAL REVIEW A}, volume = {98}, number = {3}, year = {2018}, month = {SEP 14}, pages = {033604}, issn = {2469-9926}, doi = {10.1103/PhysRevA.98.033604}, author = {Pan, Ruizhi and Clark, Charles W.} } @article { ISI:000451739700002, title = {Integration of quantum dots with lithium niobate photonics}, journal = {APPLIED PHYSICS LETTERS}, volume = {113}, number = {22}, year = {2018}, month = {NOV 26}, pages = {221102}, abstract = {The integration of quantum emitters with integrated photonics enables complex quantum photonic circuits that are necessary for photonic implementation of quantum simulators, computers, and networks. Thin-film lithium niobate is an ideal material substrate for quantum photonics because it can tightly confine light in small waveguides and has a strong electro-optic effect that can switch and modulate single photons at low power and high speed. However, lithium niobate lacks efficient single-photon emitters, which are essential for scalable quantum photonic circuits. We demonstrate deterministic coupling of single-photon emitters with a lithium niobate photonic chip. The emitters are composed of InAs quantum dots embedded in an InP nanobeam, which we transfer to a lithium niobate waveguide with nanoscale accuracy using a pick-and-place approach. An adiabatic taper transfers single photons emitted into the nanobeam to the lithium niobate waveguide with high efficiency. We verify the single photon nature of the emission using photon correlation measurements performed with an on-chip beamsplitter. Our results demonstrate an important step toward fast, reconfigurable quantum photonic circuits for quantum information processing. Published by AIP Publishing.}, issn = {0003-6951}, doi = {10.1063/1.5054865}, author = {Aghaeimeibodi, Shahriar and Desiatov, Boris and Kim, Je-Hyung and Lee, Chang-Min and Buyukkaya, Mustafa Atabey and Karasahin, Aziz and Richardson, Christopher J. K. and Leavitt, Richard P. and Loncar, Marko and Waks, Edo} } @article { ISI:000447148100013, title = {Long spin-flip time and large Zeeman splitting of holes in type-II ZnTe/ZnSe submonolayer quantum dots}, journal = {JOURNAL OF APPLIED PHYSICS}, volume = {124}, number = {14}, year = {2018}, month = {OCT 14}, pages = {144306}, issn = {0021-8979}, doi = {10.1063/1.5041478}, author = {Ji, H. and Dhomkar, S. and Wu, R. and Ludwig, J. and Lu, Z. and Smirnov, D. and Tamargo, M. C. and Bryant, G. W. and Kuskovsky, I. L.} } @article { ISI:000446561300009, title = {Long-Range Entanglement near a Kondo-Destruction Quantum Critical Point}, journal = {PHYSICAL REVIEW LETTERS}, volume = {121}, number = {14}, year = {2018}, month = {OCT 5}, pages = {147602}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.121.147602}, author = {Wagner, Christopher and Chowdhury, Tathagata and Pixley, J. H. and Ingersent, Kevin} } @article { ISI:000450258700003, title = {Low overhead Clifford gates from joint measurements in surface, color, and hyperbolic codes}, journal = {PHYSICAL REVIEW A}, volume = {98}, number = {5}, year = {2018}, month = {NOV 15}, pages = {052319}, issn = {2469-9926}, doi = {10.1103/PhysRevA.98.052319}, author = {Lavasani, Ali and Barkeshli, Maissam} } @article { ISI:000440590200010, title = {A low-steering piezo-driven mirror}, journal = {REVIEW OF SCIENTIFIC INSTRUMENTS}, volume = {89}, number = {7}, year = {2018}, month = {JUL}, pages = {073110}, issn = {0034-6748}, doi = {10.1063/1.5035326}, author = {Magnan, E. and Maslek, J. and Bracamontes, C. and Restelli, A. and Boulier, T. and Porto, J. V.} } @article { ISI:000442340900001, title = {Machine learning assisted readout of trapped-ion qubits}, journal = {JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS}, volume = {51}, number = {17}, year = {2018}, month = {SEP 14}, pages = {174006}, keywords = {ion traps, machine learning, quantum computing}, issn = {0953-4075}, doi = {10.1088/1361-6455/aad62b}, author = {Seif, Alireza and Landsman, Kevin A. and Linke, Norbert M. and Figgatt, Caroline and Monroe, C. and Hafezi, Mohammad} } @article { ISI:000435336200001, title = {Machine Learning Detection of Bell Nonlocality in Quantum Many-Body Systems}, journal = {PHYSICAL REVIEW LETTERS}, volume = {120}, number = {24}, year = {2018}, month = {JUN 14}, pages = {240402}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.120.240402}, author = {Deng, Dong-Ling} } @article { ISI:000452683500004, title = {Machine Learning Many-Body Localization: Search for the Elusive Nonergodic Metal}, journal = {PHYSICAL REVIEW LETTERS}, volume = {121}, number = {24}, year = {2018}, month = {DEC 10}, pages = {245701}, abstract = {The breaking of ergodicity in isolated quantum systems with a single-particle mobility edge is an intriguing subject that has not yet been fully understood. In particular, whether a nonergodic but metallic phase exists or not in the presence of a one-dimensional quasiperiodic potential is currently under active debate. In this Letter, we develop a neural-network-based approach to investigate the existence of this nonergodic metallic phase in a prototype model using many-body entanglement spectra as the sole diagnostic. We find that such a method identifies with high confidence the existence of a nonergodic metallic phase in the midspectrum at an intermediate quasiperiodic potential strength. Our neural-network-based approach shows how supervised machine learning can be applied not only in locating phase boundaries but also in providing a way to definitively examine the existence or not of a novel phase.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.121.245701}, author = {Hsu, Yi-Ting and Li, Xiao and Deng, Dong-Ling and S. Das Sarma} } @article { ISI:000433419500002, title = {Magnon-induced non-Markovian friction of a domain wall in a ferromagnet}, journal = {PHYSICAL REVIEW B}, volume = {97}, number = {17}, year = {2018}, month = {MAY 30}, pages = {174433}, issn = {2469-9950}, doi = {10.1103/PhysRevB.97.174433}, author = {Kim, Se Kwon and Tchernyshyov, Oleg and Galitski, Victor and Tserkovnyak, Yaroslav} } @article { ISI:000439729800001, title = {Many-body spectral reflection symmetry and protected infinite-temperature degeneracy}, journal = {PHYSICAL REVIEW B}, volume = {98}, number = {3}, year = {2018}, month = {JUL 25}, pages = {035139}, issn = {2469-9950}, doi = {10.1103/PhysRevB.98.035139}, author = {Schecter, Michael and Iadecola, Thomas} } @article { ISI:000442061000013, title = {Maximally entangled state and Bell{\textquoteright}s inequality in qubits}, journal = {ANNALS OF PHYSICS}, volume = {395}, year = {2018}, month = {AUG}, pages = {183-195}, keywords = {Bell{\textquoteright}s inequality, Maximally entangled state, Topological field theories, Topological states of matter}, issn = {0003-4916}, doi = {10.1016/j.aop.2018.05.016}, author = {Chu, Su-Kuan and Ma, Chen-Te and Miao, Rong-Xin and Wu, Chih-Hung} } @article { ISI:000418495400015, title = {Measurements of enthalpy of sublimation of Ne, N-2, O-2, Ar, CO2, Kr, Xe, and H2O using a double paddle oscillator}, journal = {JOURNAL OF CHEMICAL THERMODYNAMICS}, volume = {118}, year = {2018}, month = {MAR}, pages = {127-138}, keywords = {Argon, Carbon dioxide, Double paddle oscillator, Enthalpy of sublimation, Krypton, Neon, Nitrogen, Oxygen, Xenon and water}, issn = {0021-9614}, doi = {10.1016/j.jct.2017.11.004}, author = {Shakeel, Hamza and Wei, Haoyan and Pomeroy, J. M.} } @article { ISI:000428982800001, title = {Measuring nuclear-spin-dependent parity violation with molecules: Experimental methods and analysis of systematic errors}, journal = {PHYSICAL REVIEW A}, volume = {97}, number = {4}, year = {2018}, month = {APR 3}, pages = {042101}, issn = {2469-9926}, doi = {10.1103/PhysRevA.97.042101}, author = {Altuntas, Emine and Ammon, Jeffrey and Cahn, Sidney B. and DeMille, David} } @article { ISI:000418043100001, title = {Measuring the dielectric and optical response of millimeter-scale amorphous and hexagonal boron nitride films grown on epitaxial graphene}, journal = {2D MATERIALS}, volume = {5}, number = {1}, year = {2018}, month = {JAN}, pages = {011011}, keywords = {amorphous boron nitride, epitaxial graphene, hexagonal boron nitride, optical dielectric functions}, issn = {2053-1583}, doi = {10.1088/2053-1583/aa9ea3}, author = {Rigosi, Albert F. and Hill, Heather M. and Glavin, Nicholas R. and Pookpanratana, Sujitra J. and Yang, Yanfei and Boosalis, Alexander G. and Hu, Jiuning and Rice, Anthony and Allerman, Andrew A. and Nguyen, Nhan V. and Hacker, Christina A. and Elmquist, Randolph E. and Walker, Angela R. Hight and Newell, David B.} } @article { ISI:000451329500012, title = {Measuring the Renyi entropy of a two-site Fermi-Hubbard model on a trapped ion quantum computer}, journal = {PHYSICAL REVIEW A}, volume = {98}, number = {5}, year = {2018}, month = {NOV 26}, pages = {052334}, abstract = {The efficient simulation of correlated quantum systems is a promising near-term application of quantum computers. Here, we present a measurement of the second Renyi entropy of the ground state of the two-site Fermi-Hubbard model on a five-qubit programmable quantum computer based on trapped ions. Our work illustrates the extraction of a nonlinear characteristic of a quantum state using a controlled-swap gate acting on two copies of the state. This scalable measurement of entanglement on a universal quantum computer will, with more qubits, provide insights into many-body quantum systems t