We report on the realization of a stable mixture of ultracold lithium and ytterbium atoms confined in a far-off-resonance optical dipole trap. We observe sympathetic cooling of
6Li by
174Yb and extract the
s-wave scattering length magnitude $|{a}_{^{6}\mathrm{Li}\mathrm{\text{\ensuremath{-}}}^{174}\mathrm{Yb}}|=(13\ifmmode\pm\else\textpm\fi{}3){a}_{0}$ from the rate of interspecies thermalization. Using forced evaporative cooling of
174Yb, we achieve reduction of the
6Li temperature to below the Fermi temperature, purely through interspecies sympathetic cooling.
We have produced a quantum degenerate mixture of fermionic alkali-metal
6Li and bosonic spin-singlet
174Yb gases. This was achieved using sympathetic cooling of lithium atoms by evaporatively cooled ytterbium atoms in a far-off-resonant optical dipole trap. We observe the coexistence of Bose-condensed ($T/{T}_{\mathrm{c}}\ensuremath{\simeq}0.8$)
174Yb with $2.3\ifmmode\times\else\texttimes\fi{}{10}^{4}$ atoms and Fermi degenerate ($T/{T}_{\mathrm{F}}\ensuremath{\simeq}0.3$)
6Li with $1.2\ifmmode\times\else\texttimes\fi{}{10}^{4}$ atoms. Quasipure Bose-Einstein condensates of up to $3\ifmmode\times\else\texttimes\fi{}{10}^{4}$
174Yb atoms can be produced in single-species experiments. Our results mark a significant step toward studies of few- and many-body physics with mixtures of alkali-metal and alkaline-earth-metal-like atoms, and for the production of paramagnetic polar molecules in the quantum regime. Our methods also establish a convenient scheme for producing quantum degenerate ytterbium atoms in a 1064 nm optical dipole trap.
The prospects of sympathetic cooling of polar molecules with magnetically cotrapped alkali-metal atoms are generally considered poor due to strongly anisotropic atom-molecule interactions leading to large spin relaxation rates. Using rigorous quantum scattering calculations based on ab initio interaction potentials, we show that inelastic spin relaxation in low-temperature collisions of CaH(${}^{2}\ensuremath{\Sigma}$) molecules with Li and Mg atoms occurs at a slow rate despite the strongly anisotropic interactions. This unexpected result, which we rationalize using multichannel quantum-defect theory, opens up the possibility of sympathetic cooling of polar ${}^{2}\ensuremath{\Sigma}$ molecules with alkali-metal atoms in a magnetic trap and with alkaline-earth-metal atoms in an optical dipole trap.