A Mean-Field Treatment of Vacuum Fluctuations in Strong Light–Matter Coupling

Abstract

Mean-field mixed quantum–classical dynamics could provide a much-needed means to inexpensively model quantum electrodynamical phenomena by describing the optical field and its vacuum fluctuations classically. However, this approach is known to suffer from an unphysical transfer of energy out of the vacuum fluctuations when the light–matter coupling becomes strong. We highlight this issue for the case of an atom in an optical cavity and resolve it by introducing an additional set of classical coordinates to specifically represent vacuum fluctuations whose light–matter interaction is scaled by the instantaneous ground-state population of the atom. This not only rigorously prevents the aforementioned unphysical energy transfer but is also shown to yield a radically improved accuracy in terms of the atomic population and the optical field dynamics, generating results in excellent agreement with full quantum calculations. As such, the resulting method emerges as an attractive solution for the affordable modeling of strong light–matter coupling phenomena involving macroscopic numbers of optical modes.

Quantum to Classical Cavity Chemistry Electrodynamics

“…This observation has piqued interest in exploring how classical radiation fields might replicate the molecular dynamics typically attributed to quantum light states . Traditionally, in the study of light–matter interactions, , semiclassical methods have involved a full quantum treatment of the molecular degrees of freedom, while adopting various classical dynamics schemes for the photonic degrees of freedom. − However, recent advances employing mixed quantum-classical dynamics techniques , to solve the Ehrenfest mean-field dynamics have made strides. These techniques have demonstrated an ability to account, at least partially, for phenomena such as spontaneous emission, interference, strong coupling, and correlated light–matter dynamics. − …”