Ultracold physics and cold chemistry In ion-neutral mixtures

This thesis studies single ions inside a radio-frequency trap interacting with ultracold neutral particles. During a collision, the ion can gain energy from the time-dependent trapping field, which limits the attainable collision energies. We mitigate this effects by using Yb⁺ ions and Li atoms, the elements with the largest ion-to-atom mass ratio that allow for straightforward laser cooling. With this combination, we demonstrate buffer gas cooling of a single ion to the edge of the quantum regime and we observe non-classical behavior in atom-ion collisions.
In a second experiment, we study cold chemistry between a single ion and ultracold Li₂ Feshbach molecules. The interaction leads to fast formation of LiYb⁺ molecular ions which we detect via mass spectrometry. We show that the reaction can be used to detect as little as 50 molecules where the ion serves as a precise probe for the properties of an ultracold atomic gas.
In a theoretical part we show, that the ion trap leads to the formation of quasi-bound states during an atom-ion collision. So called complexes increase the collision time and thus impact two- and three-body reaction rates. We find that complex formation is more frequent for similar masses and for colder mixtures and it is present even in the case of time-independent traps.