Microwave photo-association spectroscopy of cesium Rydberg (n+2)D_5/2nF_J macrodimer

Rydberg atom pairs have strong long-range interactions, some of which can form potential wells that lead to bound the Rydberg-Rydberg macrodimer molecules. In this work, we report on the observation of fine-structure-mixed (FS-mixed) (n+2)D_5/2nF_J Rydberg macrodimer molecules that are bound by dipolar interactions, the longest-range multipole coupling between neutral atoms. Adiabatic potential energy curves of (n+2)D_5/2nF_J molecules are calculated by diagonalization of the Rydberg-pair Hamiltonian. We find that the strong dipolar "flip" 〈D_5/2F_J|V_dd|F_JD_5/2〉 and "cross”〈D_5/2F_7/2|V_dd|F_5/2D_5/2〉 couplings lead to bound potential wells at energies between the F_J fine-structure levels. In the experiment, we prepare the (n + 2)D_5/2 nF_J macrodimer by a microwave photo-association scheme, in which a microwave field drives a transition from an optically prepared [(n + 2)D_5/2]₂ Rydberg-pair state, which is relatively weakly-interacting, into a more strongly interacting (n + 2)D_5/2 nF_J macrodimer state. We provide spectroscopic evidence for FS-mixed DF macrodimer molecules and explain their formation mechanism. We further address Franck-Condon tuning afforded by microwave photo-association spectroscopy, and we investigate the Stark effect and the linewidths of DF macrodimer signals in weak electric fields.