Finite detection window in photon coincidence spectroscopy

Summary form only given.The Jaynes-Cummings model (JCM) of a two-level atom interacting with a single mode of a high-finesse cavity in the strong-coupling regime forms the basis of studies in strong-coupling cavity quantum electrodynamics. Jaynes and Cummings demonstrated that the semiclassical model of radiation could account for the observed properties of the coupled atom-cavity system, and it has remained a challenge to observe the nonclassical features of the JCM, specifically those that reveal quantum entanglement between the atomic internal degrees of freedom and the single-mode cavity field. The key to observing nonclassical effects is to access the nonlinear regimen of the spectrum (beyond the first couplet of the JCM ladder). This has been accomplished in the microwave domain, but the optical domain presents difficulties that are not significant in the microwave experiments. Recently, the method of photon coincidence (or correlation) spectroscopy (PCS) has been proposed to overcome these difficulties and provide an experimental signature of the nonlinear regimen of the JCM spectrum. The atom is excited directly by a bichromatic laser field, and two-photon coincidence detection is performed on the cavity output field. Here we consider the complication that arises because the two-photon de-excitation is not instantaneous: the temporal separation between the two photons in the pair is random and of the order of the cavity lifetime. We also determine the optimal window time T for detecting photon pairs in order to maximize the number of genuine pairs while minimizing the number of false pairs. Our simulations, using a Bloch function expansion for solving the master equation, yield optimal values of T.