Ultracold Fermi gases in the BEC-BCS crossover: a review from the Innsbruck perspective

By the time of the “Enrico Fermi” Summer School in June 2006, quantum degeneracy in ultracold Fermi gases has been reported by 13 groups worldwide [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]. The field is rapidly expanding similar to the situation of Bose-Einstein condensation at the time of the “Enrico Fermi” Summer School in 1998 [14]. The main two species for the creation of ultracold Fermi gases are the alkali atoms potassium (K) [1, 6, 8, 10, 11] and lithium (Li) [2, 3, 4, 5, 7, 9]. At the time of the School, degeneracy was reported for two new species, He [12] and Yb [13], adding metastable and rare earth species to the list. Fermionic particles represent the basic building blocks of matter, which connects the physics of interacting fermions to very fundamental questions. Fermions can pair up to form composite bosons. Therefore, the physics of bosons can be regarded as a special case of fermion physics, where pairs are tightly bound and the fermionic character of the constituents is no longer relevant. This simple argument already shows that the physics of fermions is in general much richer than the physics of bosons. Systems of interacting fermions are found in many areas of physics, like in condensedmatter physics (e.g. superconductors), in atomic nuclei (protons and neutrons), in primordial matter (quark-gluon plasma), and in astrophysics (white dwarfs and neutron