Semiclassical Theory of Light Detection in the Presence of Feedback

The usual open-loop semiclassical theory of light detection is extended to include closed-loop operation in which there is feedback from the detector to the source. The revised theory takes the form of a self-exciting point process. It admits photocount statistics that are associated with non-classical light in open-loop configurations, e.g., sub-shot-noise spectra and sub-Poisson photocounts. The extended theory is used to explain two recent closed-loop experiments in which sub-Poisson photocount statistics were produced.