Spontaneous decay of an excited atom in an absorbing dielectric

Starting from the quantized version of Maxwell's equations for the electrom agnetic field in an arbitrary linear Kramers-Kronig dielectric, the Heisenb eg equations of motion for a two-level atom resonantly coupled to the radia tion field in the presence of dispersive and absorbing dielectric bodies ar e derived. The theory is applied to the problem of spontaneous decay of exc ited atoms in absorbing media. The decay rate is calculated for the (Glaube r-Lewenstein) real-cavity model, and a comparison with the recently studied (Clausius-Mosotti) virtual-cavity model [S. Scheel, L. Knoll, D.-G. Welsch , and S. M. Barnett, Phys. Rev. A 60, 1590 (1999)] is given. It is shown th at owing to nonradiative decay associated with absorption, the rate of spon taneous decay sensitively depends on the cavity radius, particularly when t he atomic transition frequency approaches an absorption band of the medium. Only when the effect of absorption is fully disregarded, is the familiar l ocal-field correction factor recovered. [S1050-2947(99)03811-1].