Conditional Detection of Fluctuations of Light from an Optical Cavity with One Atom

Conditional Detection of Fluctuations of Light from an Optical Cavity with One Atom

Fluctuations of light provide a window on the underlying quantum dynamical evolution of the source emitting light. Emission of a photon by a source signals quantum fluctuations in progress. Hence a measurement that is conditioned upon a photodetection allows us to follow the time evolution of the fluctuations and the framework of conditioned measurements provides a powerful conceptual tool for understanding nonclassical features of quantum dynamics. We discuss the connection between quantum dynamics and photon fluctuations in terms of conditional measurements of intensity and field quadratures of light from a single atom in an optical cavity. Using the Fokker- Planck equation for a single atom in a high-Q cavity, we describe the light from the cavity in terms of Gaussian random variables and a coherent component. These are used to study conditional measurements of intensity and quadrature squeezing. It is found that when the coherent component is completely removed conditional light intensity shows large fluctuations, whereas conditional squeezing exhibits strong nonclassical behavior. Indeed both field quadratures exhibit nonclassical behavior. On the other hand a small coherent component results in a sizable reduction in intensity fluctuations and small squeezing.