Ultra-long-range Rydberg molecules in a divalent atomic system

We report the creation of ultra-long-range Sr-2 molecules comprising one ground-state 5s(2) S-1(0) atom and one atom in a 5sns S-3(1) Rydberg state for n ranging from 29 to 36. Molecules are created in a trapped ultracold atomic gas using two-photon excitation near resonant with the 5s5p P-3(1) intermediate state, and their formation is detected through ground-state atom loss from the trap. The observed molecular binding energies are reproduced with the aid of first-order perturbation theory that utilizes a Fermi pseudopotential with effective s-wave and p-wave scattering lengths to describe the interaction between an excited Rydberg electron and a ground-state Sr atom.