Level shifts of rubidium Rydberg states due to binary interactions

We use perturbation theory to directly calculate the van der Waals and dipole-dipole energy shifts of pairs of interacting Rb Rydberg atoms for different quantum numbers n, center dot, j, and m(j), taking into account a large number of perturbing states. Our results can be used to identify good experimental parameters and illuminate important considerations for applications of the Rydberg-excitation blockade. We also use the results of the calculation to explain features of previous experimental data on the Rydberg-excitation blockade. To explore control methods for the blockade, we discuss energy shifts due to atom-atom interaction in an external electric field.