Quantum Fluctuations in Nonlinear Optics.

Nonlinear interactions in optical physics are studied both experimentally and theoretically with particular emphasis on the quantum nature of the effects generated from them, such as photon antibunching, sub-Poissonian photon statistics, and squeezed states of light. Two conceptually simple systems with two-level atoms and a nonlinear crystal as nonlinear media are discussed. In the second system in which a nonlinear crystal inside an optical cavity forms an optical parametric oscillator, a 63% noise reduction below the vacuum noise level is directly observed. Two experiments with this squeezed light to improve the sensitivity of optical precision measurement beyond the shot-noise limit are described in detail. More than 3dB improvement in sensitivity for the detection of phase modulation is demonstrated with a Mach-Zehnder interferometer.