Fermi-Bose Quantum DegenerateK40−R87bMixture with Attractive Interaction

We report on the achievement of simultaneous quantum degeneracy in a mixed gas of fermionic ${}^{\mathrm{40}}\mathrm{K}$ and bosonic ${}^{\mathrm{87}}\mathrm{R}\mathrm{b}$. Potassium is cooled to 0.3 times the Fermi temperature by means of an efficient thermalization with evaporatively cooled rubidium. Direct measurement of the collisional cross-section confirms a large interspecies attraction. This interaction is shown to affect the expansion of the Bose-Einstein condensate released from the magnetic trap, where it is immersed in the Fermi sea.