Nonequilibrium Casimir-Polder Force in Non-Stationary Systems

TL;DR

This paper derives a quantum field theory-based Langevin equation to describe the nonequilibrium Casimir-Polder force on an atom near a substrate, highlighting the nonlocal and colored noise effects absent in previous models.

Contribution

It provides a first-principles derivation of the Langevin equation for nonstationary systems, challenging the local source hypothesis of macroscopic quantum electrodynamics.

Findings

Derived a non-equilibrium Langevin equation from quantum field theory.

Identified nonlocal and colored noise effects in atom-surface interactions.

Proposed experimental tests via atomic gas shape deformation measurements.

Abstract

Recently the Casmir-Polder force felt by an atom near a substrate under nonequilibrium stationary conditions has been studied theoretically with macroscopic quantum electrodyanamics (MQED) and verified experimentally with cold atoms. We give a quantum field theory derivation of the Langevin equation describing the atom's motion based on the influence functional method valid for fully nonequilibrium (nonstationary) conditions. The noise associated with the quantum field derived from first principles is generally colored and nonlocal, which is at variance with the `local source hypothesis' of MQED's generalization to nonequilibrium conditions. Precision measurements on the shape deformation of an atomic gas as a function of its distance from a mirror would provide a direct check of our predictions based on this Langevin equation.