  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 exhibits 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.
