TRANSIENT COHERENT POPULATION TRAPPING IN A CLOSED-LOOP INTERACTION SCHEME

We investigated the existence of coherent population trapping (CPT) as a transient effect dependent on the rate of change of interaction par ameters between an atm and light waves. For that purpose we exploited the phase dependence of CPT in a closed double-h interaction scheme, v arying the total phase of the atomic transition loop linearly in time by detuning the light waves from exact four-photon resonance. For a sl owly changing phase (that is, for small detunings) we observed the sub sequent creation and destruction of CPT depending on the varying phase , while for higher speed of phase change CPT disappears. An analytical solution for a special case for a double-h interaction scheme that ca n be used to understand the principles of this phenomenon is presented . A qualitative comparison with our experiment shows good agreement wi thin the limits of our theoretical considerations, confirming the vali dity of the basic idea.