Abstract

It is well known that spontaneous parametric down-conversion produces EPR states for photon pairs emitted in the directions where the two cones of spontaneous parametric fluorescence intersect, and therefore where two undistinguishable pairs of orthogonally polarized signal and idler photons are emitted simultaneously. This situation has strong analogies with what occurs in some circumstances in Optical Parametric Oscillators (OPOs), which are likely to oscillate simultaneously on two pairs of signal and idler modes. It can be shown that the bright output beams of the OPO have in this case strong quantum correlations on different continuous observables.

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