Final Report Summary - ATOMION (Exploring hybrid quantum systems of ultracold atoms and ions)
The project Atomion studied the immersion of a single trapped ion into a Bose-Einstein condensate of neutral atoms. One of the key achievements of the project has been the understanding of collisions and chemical reactions of neutral atoms and trapped ions at temperatures of Millikelvin, i.e. a thousands of a degree above absolute zero temperature. Previously, the study of chemical reactions between neutral and charged particles were mostly limited to much higher temperatures and also have been performed in a much less well controlled setting. Our experiments have for the first time allowed for controlling both the electronic and the spin degrees of freedom of both reaction partners, which has facilitated the most precise understanding of this type of reactions yet. Moreover, chemical reactions have been observed at the level of single particles which allowed for an understanding of the reactions without the need to average over large ensembles. We have observed that chemical reactions between neutral atoms and ions at low temperatures occur at a rate which is independent of the collision energy. This was theoretically predicted by Langevin in the early 20th century and our results have confirmed this prediction at the yet lowest temperatures. Moreover, we have demonstrated that a Bose-Einstein condensate of ultracold atoms can used as a refrigerant for trapped ions and cools them by by collisions without the presence of laser light to a low energy state in the trap.