Abstract

Coherent Population Trapping (CPT) denotes the trapping of a quantum system in a coherent superposition of states which does not interact with a set of resonant electromagnetic fields under the condition of exact multi-photon resonance [1]. If this interaction scheme is closed, ie there exists a closed path from one state to another connected by resonant excitations, the existence of such a trapping state becomes dependent on the total phase of all applied fields [2]: While for certain values of this total phase CPT still exists as a steady state of the system, for other values there is no such trapping. If now the phase changes slowly in time, there will be subsequent creation and destruction of CPT as long as the speed of change is slow compared to the response time of the quantum system. CPT then remains to be present for certain times, but does not exist for other times. For increasing speed of phase change (which can be understood also as a violation of the multiphoton resonance) CPT appears as a transient effect and becomes more and more weakly pronounced. For very high speed of phase change CPT ceases to come into existence completely.

© 1996 Optical Society of America