Final Report Summary - HYQS (Hybrid atom-ion Quantum Systems) Experiments with ultracold atoms and ions allow us to study quantum phenomena in the laboratory, such as Bose-Einstein condensation, quantum entanglement and quantum phase transitions. Although a lot of work has been done on the systems of ions and atoms separately, mixing atoms and trapped ions together and studying their interactions in the quantum regime has proven impossible up until now since the system cannot be made cold enough. Calculations revealed that mixing heavy ions with very light atoms should allow for reaching the lowest temperatures. In the project, we created a trapped ion-atom mixture composed of Yb+ and Li. This species combination has the largest mass ratio of all species that allow for straightforward laser manipulation and should therefore reach the lowest temperatures possible.We have created an experimental setup that can be used for immersing the Yb+ ions into a bath of ultracold Li atoms. We have studied the occurrence of chemical reactions between the atoms and ions and found that the rate is very low, this is beneficial for reaching the quantum regime. We have also studied the dynamics of the spin of a single ion inside a cloud of cold atoms, which indicate favorable scattering properties in the ultracold regime. We have observed the buffer gas cooling of a single ion in the cloud and found that it equilibrates at an energy that lies close to the quantum regime. We have calculated that minor improvements to our setup should allow us to reach the quantum regime. This will allow us to study the quantum dynamics of a trapped atom-ion mixture for the first time. Possible applications include the buffer-gas cooling of the trapped ion quantum computer to boost its performance, using the system as a quantum simulator of fermion-phonon coupling and studying quantum chemistry in the ultracold regime. Recently, we have also demonstrated control over the atom-ion interactions by laser-coupling the former to Rydberg states. This will allow us to couple the atom and ion quantum system together and to combine the favorable scaling prospects of the atoms with the quality and controllability of the trapped ion system. Such interactions can also be used to create repulsive atom-ion interactions, that may be used to buffer gas cool any charged particle, regardless of its mass, which could have important consequences for precision spectroscopy.
