Cooling an atom-ion hybrid system to the quantum regime
Dr. Rene Gerritsma (Van der Waals-Zeeman Instituut, Universiteit van Amsterdam, The Netherlands)

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 the trapped ion quantum computer and quantum simulation of fermion-phonon coupling [2]. Up until now, however, the ultracold temperatures required for these applications have not been reached, because the electric traps used to hold the ions cause heating during atom-ion collisions [3]. 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. For the very 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 find significant deviations from classical predictions for the temperature dependence of the spin exchange rates in these collisions. Our results open up the possibility to study trapped atom-ion mixtures in the quantum regime for the first time. 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 [4,5].

[1] M Tomza et al., arXiv:1708.07832 (2017).
[2] U. Bissbort et al., Phys. Rev. Lett. 111, 080501 (2013).
[3] M. Cetina et al., Phys. Rev. Lett. 109, 253201 (2012).
[4] T. Secker et al., Phys. Rev. Lett. 118, 263201 (2017).
[5] N. Ewald et al., arXiv:1809.03987 (2018).