Coincident count rates in absorbing dielectric media.

A study of the effects of absorption on the nonlinear process of parametric down-conversion is presented. Absorption within the nonlinear medium is accounted for by employing the framework of macroscopic QED and the Green tensor quantization of the electromagnetic field. An effective interaction Hamiltonian, which describes the nonlinear interaction of the electric field and the linear noise polarization field, is used to derive the quantum state of the light leaving a nonlinear crystal. The signal and idler modes of this quantum state are found to be a superposition of the electric and noise polarization fields. Using this state, the expression for the coincident count rates for both type-I and type-II down-conversion are found. The nonlinear interaction with the noise polarization field was shown to cause an increase in the rate on the order of 10-12 for absorption of 10% per centimeter. This astonishingly small effect is found to be negligible compared to the decay caused by linear absorption of the propagating modes. From the expressions for the biphoton amplitude, it can be seen that the maximally entangled states can still be produced even in the presence of strong absorption. [ABSTRACT FROM AUTHOR]