Perturbation theory for Wannier resonance states affected by ac field

The paper studies the effect of a weak ac field on the Wannier states, which are known to be the metastable states of a quantum particle in a periodic potential subject to a static field, Provided that the photon energy exactly matches the spacing of the Wannier-Stark ladder the system complex quasienergy spectrum is obtained. it is shown, in particular, thar a weak ac field can increase the lifetime of the Wannier states by several orders of magnitude. The analytical results of a perturbation theoretical analysis are compared against the exact numerical calculation of the system spectrum. (C) 1999 Elsevier Science B.V. All rights reserved.