Many-body delocalization in the presence of a quantum bath

TL;DR

This study experimentally investigates how a quantum bath influences many-body localization in a disordered two-dimensional ultracold bosonic system, revealing conditions under which localization persists or breaks down due to bath coupling.

Contribution

It provides the first large-scale experimental analysis of many-body delocalization caused by a quantum bath in a 2D ultracold atom system, highlighting the role of bath size and coupling.

Findings

High clean population induces delocalization of the disordered component.

Small clean population maintains localization despite coupling.

Results offer insights into thermalization and localization stability in quantum systems.

Abstract

Closed generic quantum many-body systems may fail to thermalize under certain conditions even after long times, a phenomenon called many-body localization (MBL). Numerous studies support the stability of the MBL phase in strongly disordered one-dimensional systems. However, the situation is much less clear when a small part of the system is ergodic, a scenario which also has important implications for the existence of many-body localization in higher dimensions. Here we address this question experimentally using a large-scale quantum simulator of ultracold bosons in a two-dimensional optical lattice. We prepare two-component mixtures of varying relative population and implement a disorder potential which is only experienced by one of the components. The second non-disordered ''clean'' component plays the role of a bath of adjustable size that is collisionally coupled to the ''dirty'' component. Our experiments show how the dynamics of the dirty component, which, when on its own, show strong evidence of localization, become affected by the coupling to the clean component. For a high clean population, the clean component appears to behave as an effective bath for the system which leads to its delocalization, while for a smaller clean population, the ability of the bath to destabilize the system becomes strongly reduced. Our results reveal how a finite-sized quantum system can bring another one towards thermalization, in a regime of complex interplay between disorder, tunneling and intercomponent interactions. They provide a new benchmark for effective theories aiming to capture the complex physics of MBL in the weakly localized regime.