Electric Field Effects in the Excitation of Cold Rydberg-Atom Pairs

Abstract

In this work, we study the role of the ac Stark effects on the excitation of $n{S}_{1/2}$ cold Rydberg atoms produced in a rubidium magneto-optical trap. We have observed an atomic population in the $n{P}_{3/2}$ state after excitation of $n{S}_{1/2}$ for $29\le n\le 37$. Such an observation is normally attributed to binary collisions; however, the interaction between Rb $n{S}_{1/2}$ atoms is repulsive. To explain our results, the dipole-dipole interaction and ac Stark shifts from the excitation laser must be considered. We find that the Rydberg-atom-pair state asymptotically correlating to $n{P}_{3/2}+(n-1)P_{3/2}$ is excited directly.