Biphoton electromagnetic fields and their applications

This paper describes the parametric down-conversion (PDC) effect, and some of its applications. After a brief introduction on photon statistics of electromagnetic fields, the peculiar nature of PDC emission is examined, and it is shown to consist of a pair of conjugated photons. A brief review of nonlinear optical processes from which PDC originates is given, and then some applications are discussed. A metrological application to the measurement of the quantum efficiency of photo detectors is presented in detail. Later on, some experiments of fundamental physics that make use of PDC, namely, tests of quantum mechanics, are described. Recently achieved results in both applications are discussed, as well.