Temperature-invariant Casimir-Polder forces despite large thermal photon numbers

TL;DR

This paper shows that Casimir-Polder forces near a metal surface can remain unaffected by temperature changes, even with high thermal photon numbers, due to specific quantum cancellations.

Contribution

It demonstrates temperature-invariance of Casimir-Polder potentials for molecules near surfaces, revealing a new quantum cancellation mechanism not previously understood.

Findings

Potential remains temperature-independent despite large thermal photon numbers.

Strong cancellations between nonresonant and evanescent wave components.

Contrast with atom potentials that show linear temperature dependence.

Abstract

We demonstrate that Casimir-Polder potentials can be entirely independent of temperature even when allowing for the thermal photon numbers to become large at the relevant molecular transition frequencies. This statement holds for potentials that are due to low-energy transitions of a molecule placed near a plane metal surface. For a molecule in an energy eigenstate, the temperature-invariance is a consequence of strong cancellations between nonresonant potential components and those due to evanescent waves. For a molecule with a single dominant transition in a thermal state, upward and downward transitions combine to a temperature-independent potential. The results are contrasted with the case of an atom whose potential exhibits a regime of linear temperature-dependence. Contact to the Casimir force between a weakly dielectric and a metal plate is made.