@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 { 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 { 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:000405197700004,
title = {Continuous Symmetry Breaking in 1D Long-Range Interacting Quantum Systems},
journal = {PHYSICAL REVIEW LETTERS},
volume = {119},
number = {2},
year = {2017},
month = {JUL 11},
issn = {0031-9007},
doi = {10.1103/PhysRevLett.119.023001},
author = {Maghrebi, Mohammad F. and Gong, Zhe-Xuan and Gorshkov, Alexey V.}
}
@article { ISI:000406334600006,
title = {Correlated Photon Dynamics in Dissipative Rydberg Media},
journal = {PHYSICAL REVIEW LETTERS},
volume = {119},
number = {4},
year = {2017},
month = {JUL 26},
issn = {0031-9007},
doi = {10.1103/PhysRevLett.119.043602},
author = {Zeuthen, Emil and Gullans, Michael J. and Maghrebi, Mohammad F. and Gorshkov, Alexey V.}
}
@article {ISI:000400050700001,
title = {Multicritical behavior in dissipative Ising models},
journal = {PHYSICAL REVIEW A},
volume = {95},
number = {4},
year = {2017},
month = {APR 26},
abstract = {We analyze theoretically the many-body dynamics of a dissipative Ising model in a transverse field using a variational approach. We find that the steady-state phase diagram is substantially modified compared to its equilibrium counterpart, including the appearance of a multicritical point belonging to a different universality class. Building on our variational analysis, we establish a field-theoretical treatment corresponding to a dissipative variant of a Ginzburg-Landau theory, which allows us to compute the upper critical dimension of the system. Finally, we present a possible experimental realization of the dissipative Ising model using ultracold Rydberg gases.},
issn = {2469-9926},
doi = {10.1103/PhysRevA.95.042133},
author = {Overbeck, Vincent R. and Maghrebi, Mohammad F. and Gorshkov, Alexey V. and Weimer, Hendrik}
}
@article { ISI:000414424700002,
title = {Solvable Family of Driven-Dissipative Many-Body Systems},
journal = {PHYSICAL REVIEW LETTERS},
volume = {119},
number = {19},
year = {2017},
month = {NOV 6},
issn = {0031-9007},
doi = {10.1103/PhysRevLett.119.190402},
author = {Foss-Feig, Michael and Young, Jeremy T. and Albert, Victor V. and Gorshkov, Alexey V. and Maghrebi, Mohammad F.}
}
@article {ISI:000372413300003,
title = {Causality and quantum criticality in long-range lattice models},
journal = {PHYSICAL REVIEW B},
volume = {93},
number = {12},
year = {2016},
month = {MAR 17},
pages = {125128},
chapter = {125128},
issn = {2469-9950},
doi = {10.1103/PhysRevB.93.125128},
author = {Maghrebi, Mohammad F. and Gong, Zhe-Xuan and Foss-Feig, Michael and Gorshkov, Alexey V.}
}
@article {ISI:000369217400001,
title = {Flight of a heavy particle nonlinearly coupled to a quantum bath},
journal = {PHYSICAL REVIEW B},
volume = {93},
number = {1},
year = {2016},
month = {JAN 28},
pages = {014309},
abstract = {Fluctuation and dissipation are byproducts of coupling to the {\textquoteleft}{\textquoteleft}environment.{{\textquoteright}{\textquoteright}} The Caldeira-Leggett model, a successful paradigm of quantum Brownian motion, views the environment as a collection of harmonic oscillators linearly coupled to the system. However, symmetry considerations may forbid a linear coupling, e.g., for a neutral particle in quantum electrodynamics. We argue that the absence of linear couplings can lead to a fundamentally different behavior. Specifically, we consider a heavy particle quadratically coupled to quantum fluctuations of the bath. In one dimension the particle undergoes anomalous diffusion, unfolding as a power-law distribution in space, reminiscent of Levy flights. We suggest condensed matter analogs where similar effects may arise.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.93.014309},
author = {Maghrebi, Mohammad F. and Krueger, Matthias and Kardar, Mehran}
}
@article { ISI:000369216400001,
title = {Nonequilibrium many-body steady states via Keldysh formalism},
journal = {PHYSICAL REVIEW B},
volume = {93},
number = {1},
year = {2016},
month = {JAN 27},
pages = {014307},
chapter = {014307},
issn = {2469-9950},
doi = {10.1103/PhysRevB.93.014307},
author = {Maghrebi, Mohammad F. and Gorshkov, Alexey V.}
}
@article {ISI:000375705300002,
title = {Renyi information from entropic effects in one higher dimension},
journal = {JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT},
year = {2016},
month = {APR},
pages = {043102},
abstract = {Computing entanglement entropy and its cousins is often challenging even in the simplest continuum and lattice models, partly because such entropies depend nontrivially on all geometric characteristics of the entangling region. Quantum information measures between two or more regions are even more complicated, but contain more, and universal, information. In this paper, we focus on Renyi entropy and information of the order n = 2. For a free field theory, we show that these quantities are mapped to the change of the thermodynamic free energy by introducing boundaries subject to Dirichlet and Neumann boundary conditions in one higher dimension. This mapping allows us to exploit the powerful tools available in the context of thermal Casimir effect, specifically a multipole expansion suited for computing the Renyi information between arbitrarily-shaped regions. In particular, we compute the Renyi information between two disk-shaped regions at an arbitrary separation distance. We provide an alternative representation of the Renyi information as a sum over closed-loop polymers, which establishes a connection to purely entropic effects, and proves useful in deriving information inequalities. Finally, we discuss extensions of our results beyond free field theories.},
issn = {1742-5468},
doi = {10.1088/1742-5468/2016/04/043102},
author = {Maghrebi, Mohammad F.}
}
@article { ISI:000352058600004,
title = {Fractional quantum Hall states of Rydberg polaritons},
journal = {PHYSICAL REVIEW A},
volume = {91},
number = {3},
year = {2015},
month = {MAR 31},
pages = {033838},
issn = {1050-2947},
doi = {10.1103/PhysRevA.91.033838},
author = {Maghrebi, Mohammad F. and Yao, Norman Y. and Hafezi, Mohammad and Pohl, Thomas and Firstenberg, Ofer and Gorshkov, Alexey V.}
}
@article { ISI:000339093200004,
title = {Nonequilibrium quantum fluctuations of a dispersive medium: Spontaneous emission, photon statistics, entropy generation, and stochastic motion},
journal = {PHYSICAL REVIEW A},
volume = {90},
number = {1},
year = {2014},
month = {JUL 16},
issn = {1050-2947},
doi = {10.1103/PhysRevA.90.012515},
author = {Maghrebi, Mohammad F. and Jaffe, Robert L. and Kardar, Mehran}
}
@article { ISI:000326078100006,
title = {Quantum Cherenkov radiation and noncontact friction},
journal = {PHYSICAL REVIEW A},
volume = {88},
number = {4},
year = {2013},
month = {OCT 21},
issn = {1050-2947},
doi = {10.1103/PhysRevA.88.042509},
author = {Maghrebi, Mohammad F. and Golestanian, Ramin and Kardar, Mehran}
}