Dynamics of a single ion spin impurity in a spin-polarized atomic bath

TL;DR

This study investigates spin dynamics of single Yb$^+$ ions in a cold, spin-polarized $^6$Li atomic bath, revealing strong spin-exchange interactions and providing insights into spin relaxation processes relevant for quantum regime experiments.

Contribution

It provides the first detailed experimental and theoretical analysis of spin interactions between Yb$^+$ ions and a spin-polarized atomic bath, highlighting the potential for reaching the quantum regime.

Findings

Strong spin-exchange rates polarize the ion spin after a few collisions.

Observed spin relaxation towards the $F=0$ state occurs after about 7.7 collisions.

Ab initio calculations explain the measured spin-relaxation rates.

Abstract

We report on observations of spin dynamics in single Yb$^+$ ions immersed in a cold cloud of spin-polarized $^6$Li atoms. This species combination has been proposed to be the most suitable system to reach the quantum regime in atom-ion experiments. For $^{174}$Yb$^+$, we find that the atomic bath polarizes the spin of the ion by 93(4)\,\% after a few Langevin collisions, pointing to strong spin-exchange rates. For the hyperfine ground states of $^{171}$Yb$^+$, we also find strong rates towards spin polarization. However, relaxation towards the $F=0$ ground state occurs after 7.7(1.5) Langevin collisions. We investigate spin impurity atoms as possible source of apparent spin-relaxation leading us to interpret the observed spin-relaxation rates as an upper limit. Using ab initio electronic structure and quantum scattering calculations, we explain the observed rates and analyze their implications for the possible observation of Feshbach resonances between atoms and ions once the quantum regime is reached.