Abstract

Advances in trap technology have made feasible experiments on single, or a few, atoms and ions. Photon counts from a single atom may exhibit new features that are washed out in ensembles. Wilser and I recently proposed a theoretical approach based on repeated gedanken measurements, which was then also independently proposed by Dalibard et al. and by Carmichael. The optical Bloch equations are not used but rather follow as a consequence. The approach is applied to a three-level V-system with small separation of the upper levels having parallel dipole moments. Macroscopic dark periods are predicted for such a laser-driven system, although none of the levels is metastable as in the Dehmelt system. The reason is a coherence effect. For particular values the dark period may become arbitrarily long. A similar result holds for A-systems. This explains the observed dark resonances in ensembles of such systems by increasingly long dark periods of individual atoms. The approach is then applied to atoms driven by incoherent light, and nonrate equations with off-diagonal terms are derived. It is shown that these may lead to coherence effects.

© 1992 Optical Society of America