Observation of collisions between cold Li atoms and Yb$^+$ ions

TL;DR

This study observes cold collisions between $^6$Li atoms and Yb$^+$ ions, demonstrating low charge transfer rates in ground states and providing insights into atom-ion interactions relevant for quantum technologies.

Contribution

It provides the first experimental measurements of collision rates between $^6$Li and Yb$^+$ ions, and combines these with ab initio calculations to explain the interaction potentials and reaction dynamics.

Findings

Charge transfer rate is at least 10^3 times smaller than the Langevin collision rate for ground states.

Reaction rates for excited states are dominated by charge transfer and are energy-independent in the 1-120 mK range.

Ab initio calculations qualitatively explain the low charge transfer rates and interaction potentials.

Abstract

We report on the observation of cold collisions between $^6$Li 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 $^2S_{1/2}$ ground state, the charge transfer and association rate is found to be at least~10$^{3}$ times smaller than the Langevin collision rate. These results confirm the excellent prospects of $^6$Li--Yb$^+$ for sympathetic cooling and quantum information applications. For ions prepared in the excited electronic states $^2P_{1/2}$, $^2D_{3/2}$ and $^2F_{7/2}$, we find that the reaction rate is dominated by charge transfer and does not depend on the ionic isotope nor the collision energy in the range $\sim$~1--120~mK. 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 $^2P_{1/2}$, $^2D_{3/2}$ and $^2F_{7/2}$ states. Using \textit{ab initio} methods of quantum chemistry we calculate the atom-ion interaction potentials up to energies of 30$\times 10^3$~cm$^{-1}$, and use these to give qualitative explanations of the observed rates.