Theoretical work proves that interacting quantum systems can enter a many-body localized phase in which they cannot reach thermal equilibrium without an external bath.
In the presence of strong disorder and weak interactions, closed quantum systems can enter a many-body localized phase wherein the system does not conduct heat or charge, does not equilibrate even for arbitrarily long times, and robustly violates quantum statistical mechanics. While this is well established in closed quantum systems, the interplay of such systems with delocalized degrees of freedom is much less understood. Here, the authors consider a model for which, in the noninteracting limit, some degrees of freedom are localized while others remain delocalized. Such a system can be viewed as a model for a many-body localized system brought into contact with a small bath of a comparable number of degrees of freedom. The authors numerically and analytically study the effect of interactions on this system and find that in certain parameter regimes, results are consistent with interaction-induced localization of the entire system.
Understanding under which conditions physical systems thermalize is a long-standing question in many-body physics. While generic quantum systems thermalize, there are known instances where thermalization is hindered, for example in many-body localized (MBL) systems. Here we introduce a class of stochastic collision models coupling a many-body system out of thermal equilibrium to an external heat bath. We derive upper and lower bounds on the size of the bath required to thermalize the system via such models, under certain assumptions on the Hamiltonian. We use these bounds, expressed in terms of the max-relative entropy, to characterize the robustness of MBL systems against externally-induced thermalization. Our bounds are derived within the framework of resource theories using the convex split lemma, a recent tool developed in quantum information. We apply our results to the disordered Heisenberg chain, and numerically study the robustness of its MBL phase in terms of the required bath size. The thermalization of many-body localization phases poses a number of open questions related to our understanding of thermalization in quantum systems. Here, the authors aim to demonstrate that a quantum information approach can be used to investigate the mechanisms of thermalization in a quantum many-body system when coupled to an external system.