Dipole-dipole interaction in the near-resonant Kapitza-Dirac effect

We study the near-resonant Kapitza-Dirac diffraction of two atoms interacting via the dipole-dipole interaction within the framework of an effective one-dimensional model. We concentrate mostly on the Stern-Gerlach regime of diffraction, where the atomic wave functions are sufficiently well localized that a good physical understanding of the system dynamics in terms of local potentials can be achieved. In general, the dipole-dipole interaction can lead to substantial modifications of the Stern-Gerlach diffraction pattern. We find in particular that under appropriate conditions, bound states of the atomic system can be established, with the two atoms separated by a distance of the order of hundreds of nanometers. However, spontaneous emission eventually destroys the binding between these states via a heating mechanism somewhat similar to strong-field Sysiphus heating. In this respect, the behavior of the ''diatom'' bound state under the influence of spontaneous emission is similar to that of the atomic solitons predicted to occur in near-resonant Kapitza-Dirac diffraction in the framework of nonlinear atom optics.