The quantum physics of interacting atoms and ions *

In recent years, a novel field of physics and chemistry has developed in which trapped ions and ultracold atomic gases are made to interact with each other. These systems find applications in studying quantum chemistry and collisions [1], and a number of quantum applications are envisioned such as ultracold buffergas cooling of trapped ions and quantum simulation of fermion-phonon coupling [2].

In our experiment, we overlap a cloud of ultracold 6Li atoms in a dipole trap with a 171Yb+ ion in a Paul trap. The large mass ratio of this combination allows us to suppress trap-induced heating [3]. For the first time, we buffer gas-cooled a single Yb+ ion to temperatures close to the quantum (or s-wave) limit for 6Li-Yb+ collisions. We study the temperature dependence of the spin exchange rates in these collisions and compare to theory to find estimates for the atom-ion scattering lengths. Our results open up the possibility to study trapped atom-ion mixtures in the quantum regime and to study ions interacting with weakly bound atomic Feshbach dimers [4]. Moreover, Feshbach resonances are predicted to exist between the atoms and ions that can be explored at the ultracold temperatures acquired in our lab. Finally, I will present a novel way to control interactions between atoms and ions, that employs Rydberg-coupling of the atoms to tune their polarizability [5,6].