Cooperative Effects in Rydberg Atom-Cavity Experiments
A collection of Rydberg atoms in a resonant mm-wave cavity exhibits interesting collective behaviour. If the atoms are prepared by pulsed laser pumping in the lower state of a transition resonant with the cavity mode, they constitute a transient radiation absorber for the thermal field in this mode. The absorption is a cooperative process in which the atoms behave as a very low heat capacity Bose gas. The fluctuations of this absorption process can be interpreted in terms of the Brownian motion of the collective atomic polarization subjected to the random blackbody field in the cavity.