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 Δ2p̂−=0.50(1), or −3.01(9) dB, and in the sum of phase quadratures they are Δ2q̂+=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 the discrepancies with theory are discussed.