Entropy transfer from a quantum particle to a classical coherent light field

In the field of light-matter interactions, it is often assumed that a classical light field remains almost unchanged and thus contains nearly no information about the manipulated particles. To investigate the validity of this assumption, we develop and theoretically analyze a simple Gedankenexperiment which involves the interaction of a coherent state with a quantum particle in an optical cavity. We quantify the resulting alteration of the coherent state by measuring its fidelity with the equilibrium light field state. We also apply the method of Bayesian inference to demonstrate the information transfer through photon measurements. In addition, we employ the concepts of quantum entropy and mutual information to quantify the entropy transfer from the particle to the light field. We validate the usually assumed negligible alteration of the light field and entropy transfer in the weak coupling limit. In the strong coupling limit, however, we find that the information of the initial particle state can be fully encoded in the light field. Our analysis provides a deeper understanding of the entropy exchange between quantum matter and classical light.