Long-time dynamics of self-dressing

We consider a system formed by a two-level atom initially in its bare groun d state and the electromagnetic field in the absence of radiation. The inte raction of the atom with the radiation field leads to the formation of a dr essed ground state. To describe the dynamics of self-dressing, we study the time evolution of the permanence amplitude in the initial stare. We adopt non-relativistic QED and take the atom-field interaction Hamiltonian in the minimal coupling form, within the electric dipole approximation. In order to follow the evolution of the permanence amplitude for long enough time pe riods we use the van Hove resolvent technique with appropriate partial summ ation of Feynman graphs. We show that the self-dressing process presents th e typical behaviour of a decay process and occurs with a timescale Gamma(a) (*-1), which is long compared with both the atom's inverse transition frequ ency omega(0)(-1) and the excited state decay time gamma(-1). This time is comparable with the lifetime of the excited state due to ordinary two-photo n decay. We consider the reasons for such a long time period of self-dressi ng and make comparison with previous results.