Onsager Prize (2022): Many-body localization

Many-body localization (MBL) is a type of quantum coherence, while thermalization is decoherence.  Thermalization has the upper hand, as decoherence always does, and as a result the MBL phase is in one sense very fragile.  This means that most systems that exhibit many-body localization actually do thermalize in the thermodynamic limit of large systems and (extremely!) long times.  However, many-body localization as a finite-size or finite-time effect is quite prevalent in model systems, as well as in various experiments.  Recently (Morningstar, et al., arXiv:2107.05642), we have developed a method to make better estimates of the location of the MBL phase transition in certain one-dimensional models, finding that it occurs at much weaker interactions than the numerically-seen crossover from thermalization to the finite-size MBL regime.  The physics behind this large difference can be understood in terms of many-body resonances and “avalanches”.