'Shaking' of an atom in a non-stationary cavity

We consider an atom interacting with a quantized electromagnetic field insi de a cavity with variable parameters. The atom in the ground state located in the initially empty cavity can be excited by variation of cavity paramet ers. We have discovered two mechanisms of atomic excitation. The first aris es due to the interaction of the atom with the non-stationary electromagnet ic field created by modulation of cavity parameters. If the characteristic time of variation of cavity parameters is of the order of the atomic transi tion time, the processes of photon creation and atomic excitation are going on simultaneously and hence excitation of the atom cannot be reduced to tr ivial absorption of the photons produced by the dynamical Casimir effect. T he second mechanism is 'shaking' of the atom due to fast modulation of its ground state Lamb shift which takes place as a result of fast variation of cavity parameters. The last mechanism has no connection with the vacuum dyn amical Casimir effect. Moreover, it opens a new channel of photon creation in the non-stationary cavity. Nevertheless, the process of photon creation is altered by the presence of the atom in the cavity, even if one disregard s the existence of the new channel. In particular, it removes the restricti on for creation of only even number of photons and also changes the expecta tion value for the number of created photons. Our consideration is based on a simple model of a two-level atom interacting with a single mode of the c avity field. Qualitatively our results are valid for a real atom in a physi cal cavity. (C) 2000 Elsevier Science B.V. All rights reserved.