Perturbation theory for Wannier resonance states affected by ac field

The paper studies the effect of a weak ac field on the Wannier states, whic h 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 exact ly matches the spacing of the Wannier-Stark ladder the system complex quasi energy spectrum is obtained. it is shown, in particular, thar a weak ac fie ld can increase the lifetime of the Wannier states by several orders of mag nitude. The analytical results of a perturbation theoretical analysis are c ompared against the exact numerical calculation of the system spectrum. (C) 1999 Elsevier Science B.V. All rights reserved.