Some isolated quantum systems with disordered potentials fail to ever reach thermal equilibrium, a phenomenon known as many-body localization (MBL). An outstanding question concerns the stability of this phenomenon. While it is well known that exposing the quantum system to the outside world destroys localization, it is not clear what happens when the MBL system is connected to another small quantum system known as a quantum bath. Does a quantum bath destroy the localization, and if so, how small can that bath be?
