Pulsed twin beams of light

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Abstract
Pulsed twin beams of light have been generated using an optical-parametric amplifier that is pumped by the second harmonic of a mode-locked and Q-switched neodymium:yttrium aluminum garnet laser. The intensity noise levels on the direct-detected signal and idler beams are found to be correlated by more than 15 dB, and the subtracted noise falls below the quantum limit by more than 6 dB (75%). To our knowledge, this is the first observation of pulsed twin beams of light, and yields the highest quantum-noise reduction observed in any experiment to date. Our measurements are in excellent agreement with the quantum theory of a nondegenerate optical-parametric amplifier.