Dynamical Lamb effect versus dynamical Casimir effect - art. no. 053807

An atom interacting with a quantized electromagnetic field in a cavity with time-dependent parameters is considered, Variation of the cavity parameter s results in nonstationary dynamics of the field which leads, in turn. to e xcitation of the atom, even if photons were initially absent in the cavity. We distinguish three mechanisms of such excitation: excitation due to abso rption of real photons created by the dynamical Casimir effect, excitation due to absorption of virtual photons during the transient process, and exci tation due to nonadiabatic parametric modulation of the atomic Lamb shift. The last mechanism has no relation to the dynamical Casimir effect and thus should be considered as a new vacuum QED effect. Normally all these three mechanisms give a contribution to the amplitude of the atom excitation and are accompanied by the creation of photons. Therefore the presence of an at om in the cavity alters the average number of created photons in comparison with the case of an empty non-stationary cavity. Our consideration is base d mainly on a simple model of a two-level atom interacting with a single mo de of quantized electromagnetic field. However, our results are qualitative ly valid for more realistic models.