Controlling the nature of a charged impurity in a bath of Feshbach dimers

We theoretically study the dynamics of a trapped ion that is immersed in an ultracold gas of weakly bound atomic dimers created by a Feshbach resonance. Using quasiclassical simulations, we find a crossover from dimer dissociation to molecular ion formation depending on the binding energy of the dimers. The location of the crossover strongly depends on the collision energy and the time-dependent fields of the Paul trap. Deeply bound dimers lead to fast molecular ion formation, with rates approaching the Langevin collision rate Γ′_L≈ 4.8 × 10⁻⁹ cm³s⁻¹. The kinetic energies of the created molecular ions have a median below 1mK, such that they will stay confined in the ion trap. We conclude that interacting ions and Feshbach molecules may provide an alternative approach towards the creation of ultracold molecular ions with applications in precision spectroscopy and quantum chemistry.