Casimir and Casimir-Polder forces with dissipation from first principles

TL;DR

This paper develops a first-principles approach to Casimir and Casimir-Polder forces incorporating dissipation, deriving a real-frequency integral representation and analyzing thermodynamic consistency, especially in the context of the Drude model.

Contribution

It introduces a nonperturbative, first-principles method to calculate Casimir forces with dissipation, generalizing existing formulas and examining thermodynamic implications.

Findings

Derived a real-frequency integral representation of free energy.

Showed the third law of thermodynamics holds within the approach.

Identified limitations in resolving the thermodynamic puzzle with the Drude model.

Abstract

We consider Casimir-Polder and Casimir forces with finite dissipation by coupling heat baths to the dipoles introducing, this way, dissipation from 'first principles'. We derive a representation of the free energy as an integral over real frequencies, which can be viewd as an generalization of the 'remarkable formula' introduced by Ford et. al. 1985. For instance, we obtain a nonperturbative representation for the atom-atom and atom-wall interactions. We investigate several limiting cases. From the limit $T\to0$ we show that the third law of thermodynamics cannot be violated within the given approach, where the dissipation parameter cannot depend on temperature 'by construction'. We conclude, that the given approach is insufficient to resolve the thermodynamic puzzle connected with the Drude model when inserted into the Lifshitz formula. Further we consider the transition to Matsubara representation and discuss modifications of the contribution from the zeroth Matsubara frequency.