Observation of two-photon decay of Rydberg atoms in a driven cavity

Enhanced two-photon decay has been observed for the first time in an electric dipole transition between two Rydberg levels coupled to a single mode of a strongly driven microwave cavity. This was achieved by dynamically suppressing the otherwise dominant single-photon decay. The experiment is compared with a dressed-state model which treats the external driving field exactly. Cavity-induced emission and absorption rates are calculated to fourth order in the interaction to include two-photon processes, and are found to fit the experimental data well.