Stable trapping of K, Ca+, and CaH+: Towards ground state CaH+ molecules in an ion-atom trap*

Molecular ions are good candidates for probing the time variation of fundamental constants, precision spectroscopy, and quantum information processing. For these exciting applications, the molecular ions need to be in their ground internal state and translationally cold. Laser cooling molecular ions is hindered by their rich energy level structure. We are developing an alternative and general approach to cool molecular ions using an ion-atom hybrid trap [1], where the molecular ions are trapped with laser-cooled neutral atoms and atomic ions. Coulomb interactions with calcium ions cool the translational motion of the molecular ion, and we expect collisions with cold atoms cools their internal states. We present results of charge exchange reaction between trapped Ca+ and K [2] and our progress in sympathetic rotational cooling of CaH+ ions.