Cooling of trapped ions by resonant charge exchange

TL;DR

This paper introduces resonant charge exchange as an efficient ion cooling method, demonstrating it can outperform elastic collisions in cooling trapped ions, with implications for charge transport in hybrid systems.

Contribution

The study provides experimental evidence that resonant charge exchange significantly enhances ion cooling efficiency beyond elastic collisions.

Findings

RCE cooling is two orders of magnitude more efficient per collision than EC.

Cs$^{+}$ ions are cooled more effectively by Cs atoms than by Rb atoms.

The results support future research on charge transport via electron hopping in hybrid systems.

Abstract

The two most widely used ion cooling methods are laser cooling and sympathetic cooling by elastic collisions (ECs). Here we demonstrate another method of cooling ions that is based on resonant charge exchange (RCE) between the trapped ion and the ultracold parent atom. Specifically, trapped Cs$^{+}$ ions are cooled by collisions with co-trapped, ultracold Cs atoms and, separately, by collisions with co-trapped, ultracold Rb atoms. We observe that the cooling of Cs$^{+}$ ions by Cs atoms is more efficient than cooling of Cs$^{+}$ ions by Rb atoms. This signals the presence of a cooling mechanism apart from the elastic ion-atom collision channel for the Cs-Cs$^{+}$ case, which is cooling by RCE. The efficiency of cooling by RCE is experimentally determined and the per-collision cooling is found to be two orders of magnitude higher than cooling by EC. The result provides the experimental basis for future studies on charge transport by electron hopping in atom-ion hybrid systems.