Photocount measurements as a tool for investigation of non-classical properties of twin beams

Joint signal-idler photoelectron distributions of twin beams have been measured recently in two distinct regimes: either the mean number of photon pairs per one pump pulse is lower that the number of independent modes or vice versa. Exploiting a microscopic quantum theory for joint quasi-distributions in parametric down-conversion based on the model of superposition of signal and noise we characterize properties of twin beams in terms of quasidistributions using experimental data. In parallel to the microscopic model, joint signal-idler photon-number distribution is reconstructed using the method of maximum likelihood. Negative values as well as oscillating behavior in quantum region are characteristic for the joint signal-idler quasi-distributions of integrated intensities. The larger the mean number of photon pairs per mode the weaker the quantum features are. However, they survive even in the mesoscopic regime, i.e. when tens of photon pairs per mode are present on average. Also the conditional and difference photon-number distributions are shown to be sub-Poissonian and sub-shot-noise, respectively. Violation of classical inequalities for photon-number distributions is discussed. © 2008 Copyright SPIE - The International Society for Optical Engineering.