Fermi-Bose mixtures in optical lattices: a new strongly correlated system

Quantum degenerate mixtures of fermionic and bosonic atoms represent a new class of systems offering mixed statistics and intriguing interaction features, ranging from mean-field collapse effects to strongly correlated phases with Fermion- Boson pairs forming composite Fermions. We present experimental investigations on Fermi-Bose interactions in mixtures of $^{40} $K and $^{87}$Rb atoms in harmonic trapping potentials as well as in a 3D optical lattice. In particular we discuss the first experimental observation of a localized phase of the mixture in a 3D optical lattice. This phenomenon becomes evident in the reversible loss of visibility in the interference pattern of the bosonic component, which already takes place for a shallower lattice than needed to reach the Mott insulating phase of a comparable pure bosonic system. These measurements introduce a new system to the area of strongly correlated physics and potentially connect to polaron and disorder physics.