The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. CitationRvachov Terms of UseArticle is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. We create fermionic dipolar 23 Na 6 Li molecules in their triplet ground state from an ultracold mixture of 23 Na and 6 Li. Using magnetoassociation across a narrow Feshbach resonance followed by a two-photon stimulated Raman adiabatic passage to the triplet ground state, we produce 3 × 10 4 ground state molecules in a spin-polarized state. We observe a lifetime of 4.6 s in an isolated molecular sample, approaching the p-wave universal rate limit. Electron spin resonance spectroscopy of the triplet state was used to determine the hyperfine structure of this previously unobserved molecular state. Long-Lived Ultracold Molecules with Electric and Magnetic Dipole Moments

We describe the formation of fermionic NaLi Feshbach molecules from an ultracold mixture of bosonic 23 Na and fermionic 6 Li. Precise magnetic field sweeps across a narrow Feshbach resonance at 745 G result in a molecule conversion fraction of 5% for our experimental densities and temperatures, corresponding to a molecule number of 5 × 10 4 . The observed molecular decay lifetime is 1.3 ms after removing free Li and Na atoms from the trap. The preparation and control of ultracold atoms has led to major advances in precision measurements and many-body physics. One current frontier is to extend this to diatomic molecules. Early experiments focused on homonuclear molecules, where highlights included the study of fermion pairs across the BEC-BCS crossover [1]. The preparation of heteronuclear molecules is more challenging because it requires a controlled reaction between two distinct atomic species. However, heteronuclear molecules can have a strong elecric dipole moment, which leads to a range of new scientific directions [2], including precision measurements, such as of the electron electric dipole moment [3], quantum computation mediated by dipolar coupling between molecular qubits [4] or in a hybrid system of molecules coupled to superconducting waveguides [5], many-body physics with anisotropic long-range interactions [6,7], and ultracold chemistry [8].A number of experiments have explored molecule formation in ultracold atoms using photoassociation and Feshbach resonances [2].Due to the lower abundance of fermionic alkali isotopes, only one heteronuclear fermionic molecule 40 K 87 Rb has been produced at ultracold temperatures [9]. Fermionic molecules are appealing due to Pauli suppression of s-wave collisions between identical fermions [10], as well as prospects for preparing fermions with long-range interactions as a model system for electrons with Coulomb interactions [6]. In this paper, we report the formation of a new fermionic heteronuclear molecule 23 Na 6 Li.NaLi has at least three unique features due to its constituents being the two smallest 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 [11]. Second, NaLi is reactive in its singlet X 1 Σ + ground state, meaning that the reaction NaLi + NaLi → Na 2 + Li 2 is energetically allowed [12], but with an unusually small predicted rate constant of 10 −13 cm 3 /s that is by far the lowest among all reactive heteronuclear alkali molecules [13] and should allow lifetimes > 1 s even without dipolar suppression [14]. This is related to NaLi having the smallest van der Waals C 6 coefficient of all heteronuclear alkali atom pairs [15], which results in weak scattering by the long-range potential. Finally, this slow collision rate, together with weak spin-orbit coupling in diatomic molecules with small atomic numbers Z of its constituents [16], may allow a long-lived triplet a 3 Σ + ground-state in NaLi. This state has nonzero ...

Fermi gases with repulsive interactions are characterized by measuring their compressibility as a function of interaction strength. The compressibility is obtained from in-trap density distributions monitored by phase contrast imaging. For interaction parameters kF a > 0.25 fast decay of the gas prevents the observation of equilibrium profiles. For smaller interaction parameters, the results are adequately described by first-order perturbation theory. A novel phase contrast imaging method compensates for dispersive distortions of the images.