Two of the grand challenges of modern science concern: (I) extending our quantitative understanding of matter to out-of-equilibrium scenarios, and (ii) uncovering general laws governing how complex non-equilibrium phenomena emerge from underlying physical principles. In fact, most physical systems found in nature are not in thermodynamic equilibrium, as, for instance, their inevitable coupling to the environment can give rise to fundamentally new behaviour. Understanding open quantum many-body systems poses a significant challenge, since theoretical methods capable of dealing with such scenarios are less developed and it is experimentally difficult to devise observables capable of distinguishing their vastly different types of behaviour.
We experimentally investigate the dynamics and phase structure of an open quantum systems consisting of clouds of ultracold atoms laser-excited from the ground state to a Rydberg state. The strong interplay between coherent driving, dissipation and interactions gives rise to wide variety of new phenomena.