@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 { 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: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: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 { 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: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: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: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: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 { 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}
}