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.
Highlights
Typical quantum many-body systems evolve into a locally thermal state after driven out of equilibrium by a global quench [1]
Closed generic quantum many-body systems may fail to thermalize under certain conditions even after long times, a phenomenon called many-body localization (MBL)
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
Summary
Typical quantum many-body systems evolve into a locally thermal state after driven out of equilibrium by a global quench [1]. An experiment which allows us to probe such delocalizing phenomena in a highly controlled setting and in the complex regime near the transition between the ergodic and localized phases consists of an interacting two-component mixture composed of a “dirty” component in a random potential and a “clean” component insensitive to the disorder [22,23,24]. In such a hybrid system, the clean component, which on its own would quantum thermalize, can be. While the dirty component shows strong indication of localization in the absence of a bath, the introduction of a large enough number of clean atoms alters the dynamics qualitatively, and the signs of localization vanish eventually
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