Three-photon parametric oscillator: semiclassical and quantum signatures

Summary form only given. Parametric down-conversion is the most standard source of pairs of polarization-entangled photons, which is relevant to many problems of quantum information. However, the realization of the entanglement between three or more photons is considered so far as a difficult problem. In this report we present a novel scheme for producing three-photon entangled states. The scheme involves cascaded second-order /spl chi//sup (2)/-nonlinearities inside the same twice resonant cavity pumped by a frequency /spl omega/.