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
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