Universal scaling in a strongly interacting Rydberg gas

We study a gas of ultracold atoms resonantly driven into a strongly interacting Rydberg state. The long-distance behavior of the spatially frozen effective pseudospin system is determined by a set of dimensionless parameters, and we find that the experimental data exhibit algebraic scaling laws for the excitation dynamics and the saturation of Rydberg excitation. Mean-field calculations as well as numerical simulations provide an excellent agreement with the experimental finding and are evidence for universality in a strongly interacting frozen Rydberg gas.