Steady-state properties of a driven atomic ensemble with nonlocal dissipation

In a driven dense ensemble of two-level atoms the decay acts in a correlated way on several atoms simultaneously. The competition between the coherent laser excitation and the dipole-dipole interaction induced by the dissipation gives rise to a bimodal distribution of the excitation density. More interestingly, the presence of nonlocal dissipation lifts the direct connection between the photon emission rate and the density of excited atoms present in typical open atomic systems formed by, for example, Rydberg gases or trapped ions. In contrast, here the bimodality present in the excitation density distribution, which indicates the existence of a dynamical first-order transition, is not accompanied by an intermittent behavior of the photon emission. Moreover, due to the nonlocal character of the dissipation the spatial coherence of the steady state can be measured experimentally by analyzing solely global quantities-the mean values of the photon emission rate and the density of excited atoms. We show that these effects can be experimentally probed in a system of trapped Sr atoms.