Quantum inversion of cold atoms in a microcavity

We study quantum inversion of a cold atom in the Jaynes-Cummings model when its centre-of-mass (CM) motion is described quantum mechanically. The atom and the quantized cavity mode are initially prepared in the excited state and the coherent state, respectively. Many dramatic changes take place in a tomic inversion when the atomic CM motion experiences a transition from the classical regime to the quantum regime. For ultra-cold atoms, in particula r, fine resonances are found in the inversion. This novel effect, which ori ginates from the de Broglie wave character of the atomic CM motion, is a di rect manifestation of the 'granularity' of the high-intensity cavity field. By means of the atom-field dressed-state picture, we explain the related p henomena in a qualitative way.