Entanglement in the above-threshold optical parametric oscillator
  We investigate entanglement in the above-threshold Optical Parametric Oscillator, both theoretically and experimentally, and discuss its potential applications to quantum information. The fluctuations measured in the subtraction of signal and idler amplitude quadratures are $\Delta^2 \hat p_-=0.50(1)$, or $-3.01(9)$ dB, and in the sum of phase quadratures are $\Delta^2 \hatq_+=0.73(1)$, or $-1.37(6)$ dB. A detailed experimental study of the noise behavior as a function of pump power is presented, and discrepancies with theory are discussed. 
Alessandro S. Villar, Katiuscia N. Cassemiro, Kaled Dechoum, Antonio   Z. Khoury, Marcelo Martinelli, and Paulo Nussenzveig