Resonance dispersion interaction of alkali metal atoms in Rydberg states

With the use of second-order perturbation theory in the long-range interatomic interaction for the degenerate states of two Rydberg atoms we have obtained a general formula for the dependence of atomic interaction energy on the interatomic distance R in the presence of the Forster resonance. Inside of the 'Forster sphere' (R < R-F) this dependence transforms to the formula for electric dipole interaction energy Delta Ed-d = C-3/R-3 and for R > R-F it transforms to the formula for the van der Waals interaction energy Delta E-VdW = -C-6/R-6. The van der Waals constant C-6 is represented as an expansion in terms of irreducible components which define the dependence on the interatomic axis orientation relative to the quantisation axis of projections M of the total angular momentum J. The numerical values of the irreducible components of tensor C-6 were calculated for rubidium atoms in the same Rydberg states vertical bar nlJM > with large quantum numbers n. We present the calculated resonance interaction energy of two rubidium atoms in the states vertical bar 43D(5/2M)>, whose total energy exceeds by only 8 MHz the total energy of one of the atoms in the state vertical bar 45P(3/2M)> and of the other in the state vertical bar 41F(7/2M)>.