Ultra-fast propagation of Schr\"odinger waves in absorbing media

Abstract

We identify the characteristic times of the evolution of a quantum wave generated by a point source with a sharp onset in an absorbing medium. The "traversal'' or "B\"uttiker-Landauer'' time (which grows linearly with the distance to the source) for the Hermitian, non-absorbing case is substituted by three different characteristic quantities. One of them describes the arrival of a maximum of the density calculated with respect to position, but the maximum with respect to time for a given position becomes independent of the distance to the source and is given by the particle's ``survival time'' in the medium. This later effect, unlike the Hartman effect, occurs for injection frequencies under or above the cut-off, and for arbitrarily large distances. A possible physical realization is proposed by illuminating a two-level atom with a detuned laser.