Vacuum-field atom trapping in a wide aperture spherical resonator

We consider the situation where a two-level atom is placed in the vicinity of the center of a, spherical cavity with a large numerical aperture. The vacuum field at the center of the cavity is actually equivalent to the one obtained in a microcavity, and both the dissipative and the reactive parts of the atom's spontaneous emission are significantly modified. Using an explicit calculation of the spatial dependence of the radiative relaxation rate and of the associated level shift, we show that for a weakly excitating light fields the atom cart be attracted to the center of the cavity by vacuum-induced light shifts.