Abstract

Recently the question of causality in the resonant excitation exchange between two atoms separated by a distance r was addressed by Hegcrfeldt.¹ He concluded that when one of the atoms starts in its excited state and the other in its ground state, the initially unexcited atom will have a nonvanishing excitation probability for times t < r/c. This conclusion was questioned by Milonni et al.,² who used a Heisenberg operator approach to prove that the initially unexcited atom remains unexcited for times t < r/c, provided one considers only those terms that depend on the interatomic separation r. Although this Heisenberg approach directly reveals the retardation effects, it conceals some of the interesting atom-field dynamics.

© 1997 Optical Society of America