  We observed continuous-variable entanglement between the bright beams emitted
above threshold by an ultrastable optical parametric oscillator, classically
phase-locked at a frequency difference of 161.8273240(5) MHz. The
amplitude-difference squeezing is -3 dB and the phase-sum one is -1.35 dB.
Besides proving entanglement in a new physical system, the phase-locked OPO,
such unprecedented frequency-difference stability paves the way for
transferring entanglement between different optical frequencies and densely
implementing continuous-variable quantum information in the frequency domain.
