Interaction Between Two Ground-State Atoms

We study the interatomic energy and force of two ground-state atoms in interaction with the fluctuating quantum massless scalar field in vacuum with two different approaches, i.e. the stationary perturbation theory and the DDC formalism [the formalism proposed by Dalibard, Dupont-Roc and Cohen-Tannoudji]. With the DDC formalism, we calculate the interatomic energy in terms of the contributions of vacuum fluctuations and the contributions of the atomic radiation reaction. We find that, in the near region, the contributions of vacuum fluctuations is less important than the contributions of the atomic radiation reaction, and as a result, the interatomic force is attractive and proportional to L- 3. While in the far zone, the contributions of vacuum fluctuations and those of the atomic radiation reaction become equally important, and the interatomic force is attractive and proportional to L- 4. The interatomic energy and force derived with these two different approaches are accurately the same. We comment that the two different approaches deal with the interatomic interaction from different perspectives and have their own advantages.