Superpositions of rotational states in polar molecules induce strong, long-range dipolar interactions. Here we extend the rotational coherence by nearly one order of magnitude to 8.7(6) ms in a dilute gas of polar 23 Na 40 K molecules in an optical trap. We demonstrate spin-decoupled magic trapping, which cancels first-order and reduces second-order differential light shifts. The latter is achieved with a dc electric field that decouples nuclear spin, rotation, and trapping light field. We observe density-dependent coherence times, which can be explained by dipolar interactions in the bulk gas.Interacting particles with long coherence times are a key ingredient for entanglement generation and quantum engineering. Cold and ultracold polar molecules [1][2][3][4][5][6][7][8][9][10][11] are promising systems for exploring such quantum manybody physics with long-range interactions [12,13] due to their strong and tunable electric dipole moment and long single-particle lifetime [14,15]. The manipulation of their rich internal degrees of freedom has been studied for different molecular species [16][17][18][19]. First observations include ultracold chemistry and collisions [20,21]. Nuclear spin states in the rovibronic ground state further promise exciting prospects for quantum computation due to their extremely long coherence times [22].Rotation is a particularly appealing degree of freedom for molecules because it is directly linked to their dipolar interactions. It can be manipulated by microwave (MW) fields and superpositions of rotational states with opposite parity exhibit an oscillating dipole moment with a magnitude close to the permanent electric dipole moment d 0 . Consequently, using rotating polar molecules has been proposed for quantum computation [23], to emulate exotic spin models [24] or to create topological superfluids [25].In order to make use of the rotational transition dipole in a spatially inhomogeneous optical trap, the coupling of the rotation to the trap field needs to be canceled. To first order this may be achieved by choosing an appropriate angle between the angular momentum of the molecule and the trapping field polarization ε [26] or a special trap light intensity [19] such that the differential polarizability between rotational ground and excited states is canceled. The trap is then referred to as "magic". Coherence times of about 1 ms have been achieved in bulk gases of polar molecules using these techniques [19,27]. However, this is much shorter than the dipolar interaction time, preventing observation of many-body spin dynamics.The coherence time in such a magic trap is limited by the intensity dependence of the molecular polarizabil-ity, which originates from the coupling between rotation, nuclear spins, and the trapping light field. It has been suggested to apply large magnetic [28] or electric fields [29] to reduce these couplings and thus simplify the polarizabilities of the involved states.In this work, we realize a spin-decoupled magic trap, i.e. a magic polarization angle trap wit...

Electric machines with very power-to-weight ratios are inevitable for hybridelectric aircraft applications. One potential technology that is very promising to achieve the required power-to-weight ratio for short-range aircraft, are superconductors used for high current densities in the stator or high magnetic fields in the rotor. In this paper, we present an indepth analysis of the potential for fully and partially superconducting electric machines that is based on an analytical approach taking into account all relevant physical domains such as electromagnetics, superconducting properties, thermal behavior as well as structural mechanics. For the requirements of the motors in the NASA N3-X concept aircraft, we find that fully superconducting machines could achieve 3.5 times higher power-to-weight ratio than partially superconducting machines. Furthermore, our model can be used to calculate the relevant KPIs such as mass, efficiency and cryogenic cooling requirements for any other machine design.

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Ultracold polar molecules offer strong electric dipole moments and rich internal structure, which makes them ideal building blocks to explore exotic quantum matter1–9, implement quantum information schemes10–12 and test the fundamental symmetries of nature13. Realizing their full potential requires cooling interacting molecular gases deeply into the quantum-degenerate regime. However, the intrinsically unstable collisions between molecules at short range have so far prevented direct cooling through elastic collisions to quantum degeneracy in three dimensions. Here we demonstrate evaporative cooling of a three-dimensional gas of fermionic sodium–potassium molecules to well below the Fermi temperature using microwave shielding. The molecules are protected from reaching short range with a repulsive barrier engineered by coupling rotational states with a blue-detuned circularly polarized microwave. The microwave dressing induces strong tunable dipolar interactions between the molecules, leading to high elastic collision rates that can exceed the inelastic ones by at least a factor of 460. This large elastic-to-inelastic collision ratio allows us to cool the molecular gas to 21 nanokelvin, corresponding to 0.36 times the Fermi temperature. Such cold and dense samples of polar molecules open the path to the exploration of many-body phenomena with strong dipolar interactions.