Poisson, sub-Poisson, and Bose-Einstein statistics in three-level atoms.

Abstract

A single three-level atom with the ground state strongly coupled to an excited state and weakly coupled to a third intermediate state exhibits a telegraph signal of fluorescent emission when driven by laser light at the strong coupling frequency. The ``on'' periods correspond to normal resonance fluorescence, whereas the ``off'' periods correspond to the atom being ``shelved'' in the intermediate state. Such a system has interesting statistical properties. The photon statistics during the ``on'' periods correspond to two-level behavior and are close to Poisson in nature. However, the photon number distribution of a succession of ``on'' periods exhibits Bose-Einstein statistics. Thus the three-level system can exhibit both ``quiet'' and ``noisy'' behavior. The mathematical connection between the two cases is established, and an atomic beam experiment is described which records a mixture of the two statistical extremes. The composition of the mixture is varied, and the data are shown to be well represented by an analysis based upon the model developed.