Microwave transitions from pairs of Rbnd5/2nd5/2atoms

We have observed resonant microwave transitions between pairs of atoms. Specifically, we have observed the processes $n{d}_{5/2}n{d}_{5/2}\ensuremath{\rightarrow}(n+1){d}_{j}(n\ensuremath{-}2){f}_{7/2}$ and $n{d}_{5/2}n{d}_{5/2}\ensuremath{\rightarrow}(n+2){p}_{3/2}(n\ensuremath{-}1){d}_{5/2}$ for $35\ensuremath{\le}n\ensuremath{\le}44$. These transitions are allowed due to the dipole-dipole-induced configuration interaction between the $n{d}_{5/2}n{d}_{5/2}$ state and the energetically nearby $(n+2){p}_{3/2}(n\ensuremath{-}2){f}_{7/2}$ state, which admixes some of the latter into the former. The resulting microwave transitions are analogous to two-photon transitions in which one of the photons has been replaced by the dipole-dipole interaction. We have developed a configuration interaction description of the transitions, which gives a good description of the interaction over the range $35\ensuremath{\le}n\ensuremath{\le}42$. Over this range of $n$ the detuning varies from 0.095 to 1.482 GHz, the microwave frequencies vary from 26.970 to 45.916 GHz, and the requisite microwave powers vary by a factor of over 1000.