Deep thermalization in constrained quantum systems

Abstract

Generic quantum systems thermalize as entanglement builds up between a subsystem and its complement. Performing measurements on a complementary subsystem, however, can reveal finer nuances in the system's ability to thermalize. The authors show here that systems that look `thermal' under the lens of the Eigenstate Thermalization Hypothesis (ETH) can be highly `nonthermal' when probed deeper. They illustrate this finding on several constrained models that describe slow relaxation in quantum glasses and quantum many-body scars in Rydberg atom arrays.