An apparatus for ultracold Na-40/41K mixtures toward ground-state molecule production
We present an apparatus for producing ultracold Na- 40 K and Na- 41 K mixtures as a starting point for the formation of fermionic and bosonic ground-state NaK molecules. Sodium and potassium atoms are first loaded into a magneto-optical trap and transferred to an optically plugged magnetic trap, where the mixture undergoes sympathetic cooling via radio-frequency evaporation of Na. A key feature of the apparatus is its ability to switch between loading fermionic 40 K and bosonic 41 K by toggling three acousto-optic modulators. After further sympathetic cooling in an optical dipole trap, we obtain quantum-degenerate Bose–Fermi Na- 40 K and Bose–Bose Na- 41 K mixtures. This apparatus provides a robust starting point for creating ultracold Bose and Fermi gases of ground-state NaK molecules, opening pathways to explore strongly interacting dipolar quantum matter.
We report on the preparation of a quantum degenerate mixture of 23Na40K molecules and 40K atoms. A deeply degenerate atomic mixture of 23Na and 40K atoms with a large number ratio (${N}_{F}/{N}_{B}\ensuremath{\approx}6$) is prepared in a large-volume optical dipole trap. About $3.0\ifmmode\times\else\texttimes\fi{}{10}^{4}\phantom{\rule{0.16em}{0ex}}^{23}\mathrm{Na}\phantom{\rule{0.16em}{0ex}}^{40}\mathrm{K}$ ground-state molecules are created through magnetoassociation followed by stimulated Raman adiabatic passage. The pure molecular gas is in the moderately degenerate regime. In the atom-molecule mixture, the elastic collisions provide a thermalization mechanism for the molecules. The calculated thermalization time constant is smaller than the lifetime of the molecules in the atom-molecule mixture. This indicates that the molecules may reach thermal equilibrium due to elastic atom-molecule collisions before notable losses take place. In a few tens of milliseconds, the degeneracy of the molecules is maintained. This time interval is long enough for the study of strongly interacting atom-molecule mixtures and the production of ultracold triatomic molecular gases.
We report on the realization of a degenerate mixture of ultracold fermionic lithium and chromium atoms. Based on an all-optical approach, with an overall duty cycle of about 13 s, we produce large and degenerate samples of more than $2\ifmmode\times\else\texttimes\fi{}{10}^{5}{\phantom{\rule{4pt}{0ex}}}^{6}\mathrm{Li}$ atoms and ${10}^{5}^{53}\mathrm{Cr}$ atoms, with both species exhibiting normalized temperatures of about T/TF=0.25. Additionally, through the exploitation of a crossed bichromatic optical dipole trap, we can controllably vary the density and degree of degeneracy of the two components almost independently and widely tune the lithium-to-chromium density ratio. Our $^{6}\mathrm{Li}\text{\ensuremath{-}}^{53}\mathrm{Cr}$ Fermi mixture opens the way to the investigation of a variety of exotic few- and many-body regimes of quantum matter and it appears as an optimally suited system to realize ultracold paramagnetic polar molecules, characterized by both electric and magnetic dipole moments. Ultimately, our strategy also provides an efficient pathway to produce dipolar Fermi gases, or spin mixtures, of ultracold 53Cr atoms.