BEC of $^{41}$K in a Fermi sea of $^6$Li*

We report on the production of a $^{41}$K Bose-Einstein condensate (BEC) immersed in a degenerate two-component $^6$Li Fermi sea. After evaporation in an optical dipole trap, we obtain $1.2\times10^4$ $^{41}$K atoms with a 55\% BEC fraction and a Fermi sea with $T/T_F< 0.1$, consisting of $1.8\times 10^5$ $^6$Li atoms in each of the lowest two spin states. This opens the way to study the collective behavior of a mass-imbalanced mixture of two coupled superfluids. The double-degenerate Fermi-Bose mixture also enables the study of interacting bosonic impurities in a Fermi sea. Using loss spectroscopy, we observe the $335.8\,\text{G}$ Feshbach resonance, which is comparable to the one between $^{6}$Li and the fermionic $^{40}$K isotope exploited in our previous studies on the quantum many-body dynamics of fermionic impurities in a Fermi sea \footnote{Cetina et al., Phys. Rev. Lett. \textbf{115}, 13502 (2015)}. Investigating the interacting bosonic impurities enables the direct comparison of the role of quantum statistics for fermionic and bosonic impurities.