Reduction of quantum noise in optical parametric amplification

We experimentally demonstrate that a type-II pulsed optical parametric amplifier operated in a phase-insensitive configuration works as a near-perfect classical optical amplifier whose noise figure approaches 3 dB at high gains. We further demonstrate that, when operated in a phase-sensitive configuration, this amplifier works as a quantum-optical amplifier whose noise figure goes below 3 dB and approaches 0 dB at high gains. The noise figure of 1.45 + 0.2 dB, measured for a gain of 9 dB, is clearly in the quantum regime.