Electrodynamics in cavity: resonant experiments in strong coupling regime

Two neighbouring Rydberg levels of an alkali atom coherently exchange one quantum of energy with the electromagnetic field of a high quality factor microwave cavity. Such a situation is conceptually the simplest way to observe the atom-field coupling at the elementary scale. This work presents an experimental demonstration of this interaction, in a regime where the coherent atom-field evolution dominates the damping processes. First, the atom-field coupling is described theoretically (both classically and quantum mechanically), along with some demonstrative experiments. Next, an experiment to perform spectroscopy on the first excited states of the (atom + cavity) system is described. With this device, the frequency of the energy exchange between a three-atom sample and a resonant mode of the electromagnetic field has been measured. Finally, a new experimental apparatus is presented. It makes use of the Ramsey separated oscillatory field technique and has very high spectral resolution. It will allow the observation, in the microwave domain, of the elementary coupling of a single two-level atom with a single electromagnetic field mode, in both the spectral and time domains. Moreover, the realization of this sensitive device, in which the atomic and cavity damping is negligible, will allow fundamental experiments in Quantum Mechanics (non-demolition measurements, Schroedinger cat states, etc.) to be performed using a non-resonant atom-field interaction. (author)