Quantum analysis on the four-photon interference

We present a theory for quantum interference of four photonsgenerated by spontaneous parametric down-conversion. Detailedinvestigation of the dependence of fourfold coincidence count rateon time delay between the incident and the reflective pump laserpulses is carried out. Gaussian type dependence is found, and goodagreement between our theoretical results and experimental datareported in the literature is achieved.