A quantum cable car for Wannier-Stark ladders

This Letter studies the dynamics of transitions between the levels of a Wan nier-Stark ladder induced by a resonant periodic driving. The analysis of t he problem is done in terms of resonance quasienergy states, which take int o account the metastable character of the Wannier-Stark states. It is shown that the periodic driving creates from a localized Wannier-Stark state an extended Bloch-like state with a spatial length varying in time as similar to t(1/2). Such a state can find applications in the field of atomic optics because it generates a coherent pulsed atomic beam. (C) 2000 Elsevier Scie nce B.V. All rights reserved.