We report the creation of ultra-long-range ${\mathrm{Sr}}_2$ molecules comprising one ground-state $5s^2$ ${}^1{S}_0$ atom and one atom in a $5sns$ ${}^3{S}_1$ 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 $5s5p$ ${}^3{P}_1$ 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.

• Received 26 March 2015

DOI:https://doi.org/10.1103/PhysRevA.92.031403