Vacuum energy densities of a field in a cavity with a mobile boundary

TL;DR

This paper investigates how quantum fluctuations of a mobile cavity wall influence the vacuum energy density and Casimir-Polder forces inside the cavity, highlighting the significance of wall motion and boundary conditions.

Contribution

It introduces a fully quantum mechanical model of a mobile wall in a cavity and analyzes its impact on vacuum energy densities and forces, extending previous scalar field results to electromagnetic fields.

Findings

Quantum wall fluctuations significantly alter energy density near the wall.

The effect depends on the ultraviolet cutoff related to plasma frequency.

Mobile walls modify Casimir-Polder forces, enabling experimental detection.

Abstract

We consider the zero-point field fluctuations, and the related field energy densities, inside a one-dimensional and a three-dimensional cavity with a mobile wall. The mechanical degrees of freedom of the mobile wall are described quantum mechanically and they are fully included in the overall system dynamics. In this optomechanical system, the field and the wall can interact with each other through the radiation pressure on the wall, given by the photons inside the cavity or even by vacuum fluctuations. We consider two cases: the one-dimensional electromagnetic field and the three-dimensional scalar field, and use the Green's functions formalism, which allows extension of the results obtained for the scalar field to the electromagnetic field. We show that the quantum fluctuations of the position of the cavity's mobile wall significantly affect the field energy density inside the cavity, in particular at the very proximity of the mobile wall. The dependence of this effect from the ultraviolet cutoff frequency, related to the plasma frequency of the cavity walls, is discussed. We also compare our new results for the one-dimensional electromagnetic field and the three-dimensional massless scalar field to results recently obtained for the one-dimensional massless scalar field. We show that the presence of a mobile wall also changes the Casimir-Polder force on a polarizable body placed inside the cavity, giving the possibility to detect experimentally the new effects we have considered.