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arXiv:2602.16483

Nonequilibrium Casimir-Polder Force: Motion-induced Thermal-like Effect

D. Reiche, B. Beverungen, K. Busch, F. Intravaia

quant-phSubmitted Feb 18, 2026• Announced Feb 19, 2026
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Abstract

The Casimir-Polder force is analyzed when an atom is moving at a constant velocity relative to a collection of translationally invariant macroscopic bodies with generic shapes and compositions. The interaction is described within an approach that accurately treats the atom-field coupling and accounts for the backaction from the environment onto the moving particle. Previously overlooked aspects are uncovered and linked to the nonequilibrium and nonconservative nature of the interaction. Specifically, we examine a behavior that can be understood by characterizing the underlying physical processes in terms of a motional-induced effective temperature. This phenomenon shares similarities with the Fulling-Davies-Unruh effect, opening new perspectives for the understanding of nonequilibrium physics at work in the system.

Comments
8+5 pages, 2 figures

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Acta Physica Sinica•Jan 1, 2015•0 citations
The Casimir-Polder force is analyzed when an atom is moving at a constant velocity relative to a collection of translationally invariant macroscopic bodies with generic shapes and compositions. The interaction is described within an approach that accurately treats the atom-field coupling and accounts for the backaction from the environment onto the moving particle. Previously overlooked aspects are uncovered and linked to the nonequilibrium and nonconservative nature of the interaction. Specifically, we examine a behavior that can be understood by characterizing the underlying physical processes in terms of a motional-induced effective temperature. This phenomenon shares similarities with the Fulling-Davies-Unruh effect, opening new perspectives for the understanding of nonequilibrium physics at work in the system.
The motion of a particle in vacuum near macroscopic bodies gives rise to a Magnus-like contribution to the nonequilibrium Casimir-Polder force. This effect originates from the interplay between particle dynamics and material-modified electromagnetic quantum fluctuations, inducing in the particle a direction-dependent angular momentum coupled to the electromagnetic field spin. The resulting drift force is proportional to the cross product of the particle's angular and translational velocities, revealing a rotational transport component in the nonequilibrium Casimir-Polder interaction. Our results establish a striking connection between quantum fluctuations-induced forces and the classical Magnus effect in fluid dynamics.
Casimir-Polder interactions cause energy and momentum exchange between microscopic and macroscopic bodies, a process mediated by quantum fluctuations in the coupled matter-electromagnetic field system. The dynamics of such effects are yet to be experimentally investigated due to the dominance of static effects at currently attainable atomic velocities. However, Y. Guo and Z. Jacob [Opt. Express 22, 26193 (2014)] have proposed a nonstatic two-plate setup where quantum-fluctuation-mediated effects have a strong velocity-dependent resonance, leading to a giant friction force on the plates. Here a more easily realizable setup, a moving atom between two stationary plates, is analyzed within a QED framework to establish the spectroscopic Casimir-Polder effects on the atom and their velocity dependence. While no large velocity-dependent enhancement is found, expressions for the plate-induced spectroscopic effects on the atom were found and further shown to be equivalent to the Doppler-shifted static result within certain velocity constraints. A numerical analysis investigates the behavior of this system for the well-studied case of the $6{D}_{3/2}\ensuremath{\rightarrow}7{P}_{1/2}$ transition in 133Cs^{133}\mathrm{Cs}133Cs interacting with sapphire plates.
We consider the dynamical atom-surface Casimir-Polder force in the nonequilibrium configuration of an atom near a perfectly conducting wall, initially prepared in an excited state with the field in its vacuum state. We evaluate the time-dependent Casimir-Polder force on the atom and find that it shows an oscillatory behavior from attractive to repulsive both in time and in space. We also investigate the asymptotic behavior in time of the dynamical force and of related local field quantities, showing that the static value of the force, as obtained by a time-independent approach, is recovered for times much longer than the time scale of the atomic self-dressing but shorter than the atomic decay time. We then discuss the evolution of global quantities such as atomic and field energies and their asymptotic behavior. We also compare our results for the dynamical force on the excited atom with analogous results recently obtained for an initially bare ground-state atom. We show that new relevant features are obtained in the case of an initially excited atom, for example, much larger values of the dynamical force with respect to the static one, allowing for an easier way to single out and observe the dynamical Casimir-Polder effect.
The Casimir-Polder force on a single atom in the presence of microscopic magneto-electric bodies is studied within the framework of macroscopic quantum electrodynamics. In the first part, time-independent perturbation theory is used show that the static Casimir-Polder force on a ground-state atom in the presence of an arbitrary arrangement of bodies can be expressed in terms of the atom's polarisability and the scattering part of the Green tensor characterising the bodies. This result is used to verify the origin of the force and to study various bodies of simple shapes. In the second part, a genuinely dynamical approach is developed by starting from the operator Lorentz force. It is found that the dynamics of the force on initially excited atoms is governed by irreversible spontaneous decay in the case of weak atom-field coupling, while Rabi oscillations may arise for strong atom-field coupling.
Abstract Modern laboratory techniques make possible the investigation of the role of the Casimir–Polder force in experiments on Bose–Einstein condensation and quantum reflection. Thus, it has been demonstrated that the collective oscillations of a Bose–Einstein condensate of ultracold atoms provide a sensitive probe of Casimir–Polder forces. Later, the first measurement of the temperature dependence of the Casimir–Polder force was performed in this way. The Casimir–Polder interaction plays an important role in the scattering of atoms on various surfaces. Of special interest are situations where the wave nature of an atom dominates in comparison with its classical behavior as a particle (this is referred to as quantum reflection). This chapter considers both of the latter two types of experiments in connection with the properties of the Casimir–Polder force.
Influence of the Casimir-Polder force on a slowly moving atom near a left-handed slab is discussed.We focus on an initially excited atom and its dynamic evolution during the spontaneous decay process.The left-haned slab is adopted based on two factors:(1) It provides a relatively stronger Casimir-Polder force on the excited atom far away from the interface,and(2) it can lead to an inhibited spontaneous decay rate within such a region.Therefore,we can discuss the dynamic evolution of atoms acted only by the Casimir-Polder force.The dynamic evolution discussed here includes both the evolution of atomic population and the atomic displacement.As the Casimir-Polder force depends on the atomic population,while the decay rate is related to the atomic positions,the atomic dynamic evolution is determined by its initial conditions,i.e.its position and volecity.We choose two initial positions for discussion,i.e.(1) the position with the maximum resonant Casimir-Polder force,and(2) the edge of the resonant Casimir-Polder force of the atom with dipole parallel to the interface.Furthermore,we also consider two kinds of orientations of atomic dipole,i.e.parallel and normal to the interface.It is found that the atom can be repulsed away from a surface by the Casimir-Polder force with a proper initial velocity in certain dipole orientaion during the sponatneous decay process.As the atomic dynamics depends on the orientation of the atom dipole momentum,our result can be used as a reference to distinguish atoms with different dipole momenta.Though the force discussed here exists during the spontaneous decay process,it is much different from the recoil force of the atom when it emits a photon during the spontaneous decay.The statistical average of the recoil force is null,but that of the resonant Casimir-Polder force is not.After reasonable estimation,such a Casimir-Polder force can counteract the thermal fluctuation of temperature of 15 μK during sponatneous decay.If combined with other constraint methods,it is helpful to control the dynamics of an atom more efficiently.