Thermal Casimir vs Casimir-Polder forces: Equilibrium and non-equilibrium forces

摘要

We critically discuss the common belief that the thermal Casimir-Polder forcecan always be represented as a Matsubara sum, as it is true for the Casimirforce. On the contrary, an exact treatment of the atom-field coupling revealsthat for a ground-state atom, terms associated with virtual-photon absorptioncontribute to the force which are identified as a signature of non-equilibriumdynamics. Even the equilibrium force on a thermalized atom or molecule may beoverestimated when using the ground-state polarizability instead of its thermalcounterpart.