Rydberg Atom - Rydberg Atom Dipole-Dipole Potentials

We present numerical methods to calculate dipole-dipole interaction potential curves for Rydberg atom pairs that include a background electric field, orientational effects, and do not make use of the two-state approximation. As an example, we present dipole-dipole potentials of pairs of Cs Rydberg atoms in the 89D and adjacent electronic states for internuclear separations in the $\mu$m range, for a background electric field of $\sim 28\;$mV/cm as found in a typical cold Rydberg gas created in a magneto-optical trap. It is shown that an accurate calculation of dipole-dipole potentials for Rydberg atoms requires a large basis set of atom pair states.