Temporal Dynamics of Photon Pairs Generated by an Atomic Ensemble

The time dependence of nonclassical correlations is investigated for two fields (1,2) generated by an ensemble of cold cesium atoms via the protocol of Duan et al. [Nature (London) 414, 413 (2001)]. The correlation function R(t₁,t₂) for the ratio of cross to autocorrelations for the (1,2) fields at times (t₁,t₂) is found to have a maximum value R^(max) = 292±57, which significantly violates the Cauchy-Schwarz inequality R ≤ 1 for classical fields. Decoherence of quantum correlations is observed over τ_d ≃ 175  ns, and is described by our model, as is a new scheme to mitigate this effect.