Ultracold atom-ion mixtures
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, combining the two and studying their interactions in the quantum regime is a relatively new field [1-3]. We are currently building up a new experiment that is aimed at studying the interaction between 174Yb+ ions and an ultracold gas of fermionic Li atoms. Although interactions between single ions and atoms have been studied before, our experiment is new in that it combines two species of atoms and ions that have a very large mass ratio (~29). It has been shown theoretically  that such a combination should allow reaching lower temperatures such that quantum phenomena can be studied. Reaching down to these low temperatures should also allow studying Feshbach resonances between atoms and ions.
We also aim at studying ultracold atoms interacting with crystals of trapped ions. Since Li offers a fermionic isotope, the system has stunning similarities to a natural crystalline solid and should feature solid state phenomena such as fermion-phonon coupling and quantum phase transitions [I]. This could allow us to use the system as a quantum simulator of solids and to study the dynamics of many-body atom-ion systems.
Figure: A string of ions in a Paul trap is overlapped with a cloud of ultracold Li atoms trapped by a laser beam.
For an overview of the field of hybrid atom-ion systems you can have a look at this nice review paper from the group of Johannes Hecker Denschlag.
Literature A. Grier, M. Cetina, F. Orucevic and V. Vuletic, Phys. Rev. Lett. 102, 223201 (2009).  Christoph Zipkes, Stefan Palzer, Carlo Sias & Michael Köhl, Nature 464, 388-391 (2010).  Stefan Schmidt, Arne Härter and Johannes Hecker Denschlag, Phys. Rev. Lett. 105, 133202 (2010).  M. Cetina, A. Grier and V. Vuletic, Phys. Rev. Lett. 109, 253201 (2012).
Our funding is provided by the European Research Counsil via the ERC Starting Grant Hybrid atom-ion Quantum Systems.