Mixture of bosonic and spin-polarized fermionic atoms in an optical lattice

We investigate the properties of trapped Bose-Fermi mixtures for experimentally relevant parameters in one dimension. The effect of the attractive Bose-Fermi interaction onto the bosons is to deepen the parabolic trapping potential, and to reduce the bosonic repulsion in higher order, leading to an increase in bosonic coherence. The opposite effect was observed in ${}^{87}$Rb - ${}^{40}$K experiments, most likely due to a sharp rise in temperature. We also discuss low-temperature features, such as a bosonic Mott insulator transition driven by the fermion concentration, and the formation of composite particles such as polarons and molecules.