Continuous variable entanglement of counter-propagating twin beams

This work describes the continuous-variable entanglement of the counter-propagating twin beams generated in a Mirrorless Optical Parametric Oscillator below threshold, encompassing both their quadrature and photon-number correlation. In the first case, a comparison with the single-pass co-propagating geometry outlines the huge difference of the bandwidth involved and a completely different stability of the two sources with respect to the phase-angle. In the second case, stimulated by the critical divergence of the correlation time evidenced by Corti et al., we address the issue of the temporal bandwidth of the intensity squeezing.