The Single Atom Maser and the Quantum Electrodynamics in a Cavity

Experiments on the interaction of a single atom with a single mode of a resonant electromagnetic field in a cavity are reviewed. The atoms used in these experiments were Rydberg atoms with a very large principal quantum number. Another important ingredient is a superconductivity cavity, the quality factor of which is high enough for a periodic energy exchange between atom and cavity field to be observed. The dynamics of the atom-field interaction predicted by theory was measured. Some of the features are explicitly a consequence of the quantum nature of the electromagnetic field: The statistical and discrete nature of the photon field leads to new dynamic characteristics such as collapse and revivals in the Rabi nutation.