Thermodynamics of light emission

Abstract

Some interactions between classical or quantum fields and matter are known to be irreversible processes. Here we associate an entropy to the electromagnetic field from well-known notions of statistical quantum mechanics, in particular the notion of diagonal entropy. We base our work on the study of spontaneous emission and light diffusion. We obtain a quantity which allows to quantify irreversibility for a quantum and classical description of the electromagnetic field, that we can study and interpret from a thermodynamical point of view.