Ion loss events in a cold Rb-Ca$^+$ hybrid trap: photodissociation, black-body radiation and non-radiative charge exchange

TL;DR

This paper models the collisional processes in a hybrid Rb-Ca$^+$ trap, explaining ion loss mechanisms, the stability of molecular ions against photodissociation, and confirming non-radiative charge exchange as the main loss process.

Contribution

It provides a theoretical analysis of ion loss mechanisms in a specific hybrid trap, incorporating new molecular data and explaining experimental observations.

Findings

Molecular ions are protected from photodissociation by black-body radiation and the cooling laser.

Non-radiative charge exchange is confirmed as the dominant ion loss process.

Theoretical rates agree with experimental data.

Abstract

We theoretically investigate the collisional dynamics of laser-cooled $^{87}$Rb ground-state atoms and $^{40}$Ca$^+$ ground-state ions in the context of the hybrid trap experiment of Ref. [Phys. Rev. Lett. 107, 243202 (2011)], leading to ion losses. Cold $^{87}$Rb$^{40}$Ca$^+$ ground-state molecular ions are created by radiative association, and we demonstrate that they are protected against photodissociation by black-body radiation and by the $^{40}$Ca$^+$ cooling laser at 397~nm. This study yields an interpretation of the direct observation of $^{87}$Rb$^{40}$Ca$^+$ ions in the experiment, in contrast to other hybrid trap experiments using other species. Based on novel molecular data for the spin-orbit interaction, we also confirm that the non-radiative charge-exchange is the dominant loss process for Ca$^+$ and obtain rates in agreement with experimental observations and a previous calculation.