Experimental demonstration of frequency-degenerate bright EPR beams with   a self-phase-locked optical parametric oscillator
  We report the first experimental observation of bright EPR beams produced by a type-II optical parametric oscillator operating above threshold at frequency degeneracy. The degenerate operation is obtained by introducing a birefringent plate inside the cavity resulting in phase locking. After filtering the pump noise, which plays a critical role, continuous-variable EPR correlations between the orthogonally polarized signal and idler beams are demonstrated. 
Gaelle Keller (LKB - Jussieu), Virginia D'Auria (LKB - Jussieu),   Nicolas Treps (LKB - Jussieu), Thomas Coudreau (MPQ), Jul...