Two methods for detecting nonclassical correlations in parametric scattering of light

Two methods for studying nonclassical correlations at the output of a two-mode parametric amplifier-first, the measurement of normalized Glauber correlation functions and, second, the measurement of the variance of the photon-number difference in conjugate modes-are compared. It is shown theoretically and experimentally that the corresponding quantities, the normalized correlation function, and the noise reduction factor have significantly different dependences on the main system parameters such as the parametric gain, optical losses, photo-detector quantum efficiency, and the detected angular and frequency bands.