Quantum many-body scars and weak breaking of ergodicity

Serbyn, Maksym; Abanin, Dmitry A.; Papić, Zlatko

doi:10.1038/s41567-021-01230-2

Cited by 330 publications

(204 citation statements)

References 95 publications

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“…In recent years, progress in the development of experimental simulation platforms [2], including trapped ions [3,4] and ultracold atomic gases [5,6], has opened the door to the study of far-from-equilibrium manybody quantum dynamics [7]. Theoretical and experimental investigations have led to the discovery of a wealth of novel non-equilibrium quantum phenomena, such as the strong [8,9] or weak [10,11] breaking of ergodicity, generalized hydrodynamics describing integrable systems [12,13] and discrete time crystals [14].…”

Section: Introductionmentioning

confidence: 99%

Entanglement View of Dynamical Quantum Phase Transitions

2021

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Non-analytic points in the return probability of a quantum state as a function of time, known as dynamical quantum phase transitions (DQPTs), have received great attention in recent years, but the understanding of their mechanism is still incomplete. In our recent work .040602], we demonstrated that one-dimensional DQPTs can be produced by two distinct mechanisms, namely semiclassical precession and entanglement generation, leading to the definition of precession (pDQPTs) and entanglement (eDQPTs) dynamical quantum phase transitions. In this manuscript we extend and investigate the notion of p-and eDQPTs in two-dimensional systems by considering semi-infinite ladders of varying width. For square lattices, we find that pDQPTs and eDQPTs persist and are characterized by similar phenomenology as in 1D: pDQPTs are associated with a magnetization sign change and a wide entanglement gap, while eDQPTs correspond to suppressed local observables and avoided crossings in the entanglement spectrum. However, DQPTs show higher sensitivity to the ladder width and other details, challenging the extrapolation to the thermodynamic limit especially for eDQPTs. Moving to honeycomb lattices, we also demonstrate that lattices with odd number of nearest neighbors give rise to phenomenologies beyond the one-dimensional classification.

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Section: Introductionmentioning

confidence: 99%

Entanglement View of Dynamical Quantum Phase Transitions

2021

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“…More recently, quantum many-body scarring has emerged as another remarkable ergodicity-breaking phenomenon, where preparing the system in special initial states effectively traps it in a "cold" subspace that does not mix with the thermalizing bulk of the spectrum [7,8]. Such behavior hinders the scrambling of information encoded in the initial state and suppresses the spreading of quantum entanglement, allowing a many-body system to display persistent quantum revivals.…”

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confidence: 99%

Observation of unconventional many-body scarring in a quantum simulator

Su¹,

Hudomal²,

Desaules³

et al. 2022

Preprint

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The ongoing quest for understanding nonequilibrium dynamics of complex quantum systems underpins the foundation of statistical physics as well as the development of quantum technology. Quantum many-body scarring has recently opened a window into novel mechanisms for delaying the onset of thermalization, however its experimental realization remains limited to the Z2 state in a Rydberg atom system. Here we realize unconventional many-body scarring in a Bose-Hubbard quantum simulator with a previously unknown initial condition -the unit-filling state. Our measurements of entanglement entropy illustrate that scarring traps the many-body system in a low-entropy subspace. Further, we develop a quantum interference protocol to probe out-of-time correlations, and demonstrate the system's return to the vicinity of the initial state by measuring single-site fidelity. Our work makes the resource of scarring accessible to a broad class of ultracold-atom experiments, and it allows to explore its relation to constrained dynamics in lattice gauge theories, Hilbert space fragmentation, and disorder-free localization.

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“…In this way, subsystems can be in thermal equilibrium with the remaining system and expectation values of local observables then agree with those from conventional quantum statistical mechanics. While the eigenstate thermalization hypothesis makes powerful predictions about a large class of quantum systems, it is violated by various mechanisms, such as quantum integrability, many-body localization (MBL) [4,7], and quantum many-body scars [8][9][10]. MBL is typically achieved by introducing disorder into suitably chosen systems.…”

Section: Introductionmentioning

confidence: 99%

Escaping many-body localization in an exact eigenstate

Srivatsa¹,

Iversen²,

Nielsen³

2022

Preprint

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Closed quantum systems typically follow the eigenstate thermalization hypothesis, but there are exceptions, such as many-body localized (MBL) systems and quantum many-body scars. Here, we present the study of a weak violation of MBL due to a special state embedded in a spectrum of MBL states. The special state is not MBL since it displays logarithmic scaling of the entanglement entropy and of the bipartite fluctuations of particle number with subsystem size. In contrast, the bulk of the spectrum becomes MBL as disorder is introduced. We establish this by studying the mean entropy as a function of disorder strength for eigenstates in the middle of the spectrum and by observing that the adjacent gap ratio undergoes a transition from the value for Wigner-Dyson statistics to the value for Poisson statistics as the disorder strength is increased. When the Hamiltonian is perturbed in such a way that the special state is no longer an eigenstate, the weak violation of MBL disappears, which suggests that the partial solvability of the model together with the particular form of the state are the source of the violation.

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Quantum many-body scars and weak breaking of ergodicity

Cited by 330 publications

References 95 publications

Entanglement View of Dynamical Quantum Phase Transitions

Entanglement View of Dynamical Quantum Phase Transitions

Observation of unconventional many-body scarring in a quantum simulator

Escaping many-body localization in an exact eigenstate

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