Molecular Resonances due to Long-Range Interactions between Ultracold Rydberg Atoms

Molecular resonances have previously been observed in the spectroscopy of cold dense Rydberg gases [1]. These are due to avoided crossings between interatomic potentials which originate at various doubly-excited asymptotes. In the vicinity of transitions to Rb \textit{np} atomic Rydberg states ($n\sim $70), we have recently seen multiple molecular resonances which correspond to various pairs of highly-excited states. Examples of these combinations include ($n$-1)$d$+\textit{ns} and ($n$-1)$p$+($n$+1)$p$. We will report on measurements of these and other resonances as well as modeling of the spectra based on the long-range interatomic potentials and the strong couplings between them. [1] S.M. Farooqi, et al., Phys. Rev. Lett. \textbf{91}, 183002 (2003).