Observation of unconventional many-body scarring in a quantum simulator

Abstract

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.

Weak Ergodicity Breaking in the Schwinger Model

“…4 for S = 1/2 to 2 show strikingly nonthermal behavior for quenches starting in |0 − . Indeed, over the timescales we simulate there are persistent oscillations in the signal and no equilibration, in agreement with experimental results for the spin-1/2 U(1) QLM [1,4]. The oscillations in C(t) have twice the frequency of the fidelity revivals.…”

“…In this Letter, we show that QMBS survive at any value of S. For a zero-mass quench, QMBS arise when the system is prepared in the extreme vacua of the spin-S U(1) QLM, which are the most highly excited vacuum states of lattice QED. Furthermore, we find that preparing the system in the physical (least excited) vacua or in the charge-proliferated state can still lead to detuned scarring behavior for certain massive quenches, similar to the case of S = 1/2 that has recently been demonstrated experimentally in a tilted Bose-Hubbard optical lattice [4]. Our results indicate that QMBS may persist toward the limit of lattice QED, S → ∞.…”

“…As shown in Fig. 5, the overlap of these initial states with the eigenstates of the quench Hamiltonian (1) at µ = 0.486J and g 2 = 0.6J shows distinctive towers equally spaced in energy, similar to the known case of S = 1/2 [4]. Also displayed in Fig.…”

“…Detuned scarring.-In a recent study [4], it has been shown theoretically and demonstrated experimentally that there are scarring regimes beyond the resonant one discussed above. This was demonstrated in the spin-1/2 U(1) QLM by starting in the charge-proliferated state and performing a quench at finite mass (detuning).…”

“…Introduction.-Quantum many-body scars (QMBS) form an intriguing paradigm of ergodicity breaking in interacting systems that are typically expected to thermalize due to their nonintegrability and spatial homogeneity [1][2][3][4][5]. QMBS comprise eigenstates of low entanglement entropy [6,7], many of which reside in the middle of the spectrum, and are often separated roughly equally in energy [8,9].…”