New asymptotic behaviour of the surface-atom force out of thermal equilibrium

TL;DR

This paper derives a new asymptotic form of the surface-atom force out of thermal equilibrium, showing a slower decay, temperature dependence, and potential for attraction or repulsion, relevant for ultracold atom experiments.

Contribution

It presents a novel analysis of the Casimir-Polder-Lifshitz force out of thermal equilibrium, revealing a different decay law and temperature effects not previously characterized.

Findings

Force decays as 1/z^3 at large distances

Force exhibits significant temperature dependence

Force can be attractive or repulsive depending on substrate and environment temperatures

Abstract

The Casimir-Polder-Lifshitz force felt by an atom near the surface of a substrate is calculated out of thermal equilibrium in terms of the dielectric function of the material and of the atomic polarizability. The new force decays like $1/z^3$ at large distances (i.e. slower than at equilibrium), exhibits a sizable temperature dependence and is attractive or repulsive depending on whether the temperature of the substrate is higher or smaller than the one of the environment. Our predictions can be relevant for experiments with ultracold atomic gases. Both dielectric and metal substrates are considered.