Reactive two-body and three-body collisions of Ba$^+$ in an ultracold Rb gas

TL;DR

This study measures and distinguishes two-body and three-body reactive collision rates of Ba$^+$ ions with ultracold Rb atoms, providing key data for understanding ion-atom interactions at ultracold temperatures.

Contribution

First experimental determination of both two-body and three-body reactive collision rate coefficients for Ba$^+$ and Rb at ultracold temperatures.

Findings

Three-body recombination dominates over binary reactions at moderate densities.

Measured two-body rate coefficient: $k_2=3.1(6)(6)\times 10^{-13}\textrm{cm}^{3}\textrm{s}^{-1}$.

Measured three-body rate coefficient: $k_3=1.04(4)(45)\times 10^{-24}\textrm{cm}^{6}\textrm{s}^{-1}$.

Abstract

We analyze reactive collisions of a single Ba$^+$ ion in contact with an ultracold gas of Rb atoms at low three-body collision energies of 2.2(9) mK$\times k_{\mathrm{B}}$. Mapping out the Ba$^+$ loss rate dependence on the Rb atom density we can discern two-body reactive collisions from three-body ones and for the first time determine both rate coefficients which are $k_2=3.1(6)(6)\times 10^{-13}\textrm{cm}^{3}\textrm{s}^{-1}$ and $k_3=1.04(4)(45)\times 10^{-24}\textrm{cm}^{6}\textrm{s}^{-1}$, respectively (statistical and systematic errors in parenthesis). Thus, the measured ternary recombination dominates over binary reactions even at moderate atom densities of $n\approx 10^{12}\: \textrm{cm}^{-3}$. The results for Ba$^+$ and Rb are representative for a wide range of cold ion-atom systems and can serve as a guidance for the future development of the field of hybrid atom-ion research.