Diffusive to Nonergodic Dipolar Transport in a Dissipative Atomic Medium

We investigate the dipole-mediated transport of Rydberg impurities through an ultracold gas of atoms prepared in an auxiliary Rydberg state. In one experiment, we continuously probe the system by coupling the auxiliary Rydberg state to a rapidly decaying state that realizes a dissipative medium. In situ imaging of the impurities reveals diffusive spreading controlled by the intensity of the probe laser. By preparing the same density of hopping partners, but then switching off the dressing fields, the spreading is effectively frozen. This is consistent with numerical simulations, which indicate the coherently evolving system enters a nonergodic extended phase. This opens the way to study transport and localization phenomena in systems with long-range hopping and controllable dissipation.