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Formation of Ultracold Fermionic NaLi Feshbach Molecules
We have produced NaLi Feshbach molecules from an ultracold mixture of bosonic 23Na and fermionic 6Li [1]. Precise magnetic field sweeps across a narrow Feshbach resonance convert 5% of free atoms into weakly bound molecules, corresponding to a molecule number of 5 × 104. NaLi is only the second fermionic heteronuclear molecule produced at ultracold temperatures, and has several unique features due to its constituents being the lightest alkali atoms. First, its small reduced mass gives it a large rotational constant, which suppresses inelastic molecule-molecule collisions that occur via coupling between rotational levels [2]. Second, NaLi in its singlet ground state undergoes exothermic reactions NaLi + NaLi → Na2 + Li2, but with an unusually small predicted rate constant [3], due to the smallness of van der Waals interactions in NaLi [4], that will allow long lifetimes >1s even without dipolar suppression. This slow collision rate, together with weak spin-orbit coupling, may allow a long-lived triplet ground-state in NaLi, which has nonzero electric and magnetic dipole moments and will open up the possibility of exploring novel physics such as magnetic and electric field control of molecule-molecule collisions.