WEAK ATOM-ATOM INTERACTION POTENTIAL FROM THE MASTER EQUATION FOR RADIATION COUPLED TO THE ATOMS

It is shown how the asymptotic interatomic potential, that is the term varying as R-7 in the Casimir potential, arises from a master equation approach. The density matrix equation for the combined radiation and atoms is approximated by a master equation for the radiation density matrix obtained by tracing over the states of the reservoir consisting of a dilute gas of atoms. By extracting a common frequency shift, which depends on the atomic positions, for all diagonal elements of the reduced density matrix the energy shift for the dilute gas is seen to be a pairwise sum over the atoms of the R-7 potential. © 1979.