Physical Review A
Exact property of the nonequilibrium photon Green function for bounded media
K. Henneberger, F. Richter
Abstract
The photon Green function for a system consisting of a bounded medium surrounded by vacuum is analyzed on the basis of the Dyson equation. It is found that the fluctuations of the light field decompose universally into contributions arising from generation and recombination processes in the medium, and those arising from an external electromagnetic stimulation, i.e., light incident from the vacuum. This proves to be advantageous for further quantum-kinetically exact analysis of the interplay in the coupled system of light and matter. Particularly, it is shown that arbitrary (even nonclassical) externally induced light always propagates according to the classical wave propagation problem. These results are valid for arbitrary nonequilibrium situations, regardless of specific optical properties or geometrical shapes of the matter. For demonstration, exact relations for the scattering of squeezed light by a steady-state semiconductor slab are derived on this footing.