Magnetism is a macroscopic phenomenon with its origin deeply rooted in quantum mechanics. In condensed matter physics, there are two paradigms for magnetism: localized spins interacting via tunnelling, and delocalized spins interacting via an exchange energy. The latter gives rise to itinerant ferromagnetism which is responsible for the properties of transition metals 1

The recombination of two split Bose-Einstein condensates on an atom chip is shown to result in heating which depends on the relative phase of the two condensates. This heating reduces the number of condensate atoms between 10% and 40% and provides a robust way to read out the phase of an atom interferometer without the need for ballistic expansion. The heating may be caused by the dissipation of dark solitons created during the merging of the condensates.

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 ...