Abstract
The so-called remarkable formula [G. W. Ford, J. T. Lewis, and R. F. O'Connell, Phys. Rev. Lett. 55, 2273 (1985)] for the Helmholtz free energy is applied to the problem of determining the interaction potential to all orders in the coupling strength of a pair of oscillator dipoles interacting through the familiar dipole-dipole interaction of electrodynamics. Simple, straightforward calculations lead to expressions for (1) the London short-range potential, (2) the Casimir-Polder long-range potential, and (3) the potential at high temperature. Explicit results are shown for both the temperature dependence of the interaction potential and its deviation from the weak-coupling limit. It is stressed that the interaction potential is a change in free energy, not the energy; in particular, in the high temperature case, the change of energy is zero.
- Received 10 December 2013
DOI:https://doi.org/10.1103/PhysRevA.89.022127
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