Extremely dilute, but strongly correlated: Experiments with ultracold fermions

by Prof. Selim Jochim (MPI for Nuclear Physics, Heidelberg, Germany)

Monday 29 Nov 2010, 08:00 → 09:00 Europe/Budapest

2nd floor Tanácsterem (MTA KFKI RMKI Building III)

Abstract: Ultracold gases have been a fantastic playground for studying strongly interacting many-body systems, largely because the interaction strength between the atoms could be tuned at wish using so-called Feshbach resonances. In particular, researchers succeeded to prepare fermionic gases in which the scattering length is much bigger than the interparticle spacing, which in turn is much larger than the range of the van-der-Waals interaction. This generic system created in this way allowed the study of complex many-body phenomena. The most prominent example was the BEC-BCS crossover, which establishes a continuous link between the phenomena of superfluidity of bosons and of the superconductivity of fermions. Two-component mixtures of fermions with infinite scattering length have been found to behave like an almost perfect fluid with viscosities eta/s being close to the expected theoretical limits. In our current experiments we study Fermi gases composed of three distinguishable particles. At very large scattering length these systems exhibit an approximate SU(3) symmetry, and they can be used as a simplified model for quark matter. In our experiments, we have studied the few-body physics of that system and found it to be governed by so-called Efimov trimers, universal three-body bound states whose properties are determined by the interparticle scattering length and a three-body parameter. Recently, we directly observed such states for the first time an measured their binding energy as a function of interaction strength*. Currently, we are setting up an experiment that should allow us to study many-body physics in that system, such as color superconductivity.