Observation of unconventional many-body scarring in a quantum simulator

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 $\mathbb{Z}_2$

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.