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

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.