Irreversibility of energy-conservative dipole dephasing in a simple model

Abstract

Abrupt radiative excitation into a one-electron atomic continuum of distinct zero-width energy levels is investigated in a simple energy-conservative atomic model. Induced off-diagonal coherence is shown to decay irreversibly. That is, it is shown that one cannot recover off-diagonal coherence by the application of subsequent radiative pulses, ruling out the occurrence of long-time or repetitive coherent transients such as photon echoes in this model of continuum transitions. A brief comparison with the case of transitions in a Doppler-broadened continuum, where coherent transients are commonly observed, is made.