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

TL;DR

This paper investigates how a quantum particle can transfer entropy to a classical light field during interaction, challenging the assumption that classical fields remain unaffected and nearly contain no information about quantum particles.

Contribution

The study introduces a theoretical framework analyzing entropy transfer from quantum particles to classical light, revealing conditions where information encoding is maximized.

Findings

Entropy transfer is negligible in weak coupling

Full encoding of particle information occurs in strong coupling

Spontaneous emission removes initial particle entropy

Abstract

In the field of light-matter interactions, it is often assumed that a classical light field that interacts with a quantum particle 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 light field by measuring the fidelity of its initial and equilibrium states. Using Bayesian inference, we 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. In the weak coupling limit, we validate the usually assumed negligible alteration of the light field and entropy transfer. In the strong coupling limit, however, we observe that the information of the initial particle state can be fully encoded in the light field, even for large photon numbers. Nevertheless, we show that spontaneous emission is a sufficient mechanism for removing the entropy initially stored in the particle. Our analysis provides a deeper understanding of the entropy exchange between quantum matter and classical light.