We present a Heisenberg-picture approach to the electric dipole interaction of two generally nonidentical atoms, one of which is initially excited, and address the question of whether the dependence of the interaction energy on the interatomic separation $r$ is purely monotonic or is sinusoidally modulated as it falls off with $r$. We derive energies of both types and associate them with different model assumptions and physical effects. The sinusoidally modulated form is the interaction energy involved in reversible exchange of excitation (“pendulation”). The monotonic form characterizes an energy shift associated with effectively irreversible (Förster) excitation transfer.

• Received 3 November 2015

DOI:https://doi.org/10.1103/PhysRevA.92.062711