Observation of collisions between cold Li atoms and Yb+ ions

We report on the observation of cold collisions between 6Li atoms and Yb+ ions. This combination of species has recently been proposed as the most suitable for reaching the quantum limit in hybrid atom-ion systems, due to its large mass ratio. For atoms and ions prepared in the 2S1/2 ground state, the charge-transfer and association rate is found to be at least 103 times smaller than the Langevin collision rate. These results confirm the excellent prospects of 6Li−Yb+ for sympathetic cooling and quantum information applications. For ions prepared in the excited electronic states 2P1/2, 2D3/2, and 2F7/2, we find that the reaction rate is dominated by charge transfer and does not depend on the ionic isotope or the collision energy in the range ∼1–120mK. The low charge-transfer rate for ground-state collisions is corroborated by theory, but the 4f shell in the Yb+ ion prevents an accurate prediction for the charge-transfer rate of the 2P1/2, 2D3/2, and 2F7/2 states. Using ab initio methods of quantum chemistry we calculate the atom-ion interaction potentials up to energies of 30×103cm−1, and use these to give qualitative explanations of the observed rates.