Competing excitation quenching and charge exchange in ultracold Li-Ba$^+$ collisions

TL;DR

This study investigates complex collision processes between a metastable Ba$^+$ ion and ultracold Li atoms, revealing competing non-radiative mechanisms and demonstrating a detailed quantum model that aligns well with experimental results.

Contribution

It provides the first combined experimental and theoretical analysis of metastable Ba$^+$ and ultracold Li collisions, highlighting complex competing processes and developing a comprehensive quantum model.

Findings

Multiple non-radiative processes compete during collisions.

Quantum model accurately predicts experimental observations.

Strong coupling between internal angular momenta and rotation observed.

Abstract

Hybrid atom-ion systems are a rich and powerful platform for studying chemical reactions, as they feature both excellent control over the electronic state preparation and readout as well as a versatile tunability over the scattering energy, ranging from the few-partial wave regime to the quantum regime. In this work, we make use of these excellent control knobs, and present a joint experimental and theoretical study of the collisions of a single $^{138}$Ba$^+$ ion prepared in the $5d\,^2D_{3/2,5/2}$ metastable states with a ground state $^6$Li gas near quantum degeneracy. We show that in contrast to previously reported atom-ion mixtures, several non-radiative processes, including charge exchange, excitation exchange and quenching, compete with each other due to the inherent complexity of the ion-atom molecular structure. We present a full quantum model based on high-level electronic structure calculations involving spin-orbit couplings. Results are in excellent agreement with observations, highlighting the strong coupling between the internal angular momenta and the mechanical rotation of the colliding pair, which is relevant in any other hybrid system composed of an alkali-metal atom and an alkaline-earth ion.