One such system is a Bose-Einstein condensate with spin-orbit coupling, which has a supersolid stripe phase 5-8 . Despite several recent studies of this system 9-11 , which studied the miscibility of the spin components 5 , the presence of stripes has not been detected. Here we report the direct observation of the predicted density modulation of the stripe phase using Bragg reflection. Our work establishes a system with * These authors contributed equally to this work. § junruli@mit.edu † Although the original observation of supersolidity 3 turned out to be caused by unusual elastic properties, experiments revealed quantum plasticity and mass supertransport, probably created by superfluid flow through the cores of interconnected dislocations 1,4
Arrays of single ultracold molecules promise to be a powerful platform for many applications ranging from quantum simulation to precision measurement. Here we report on the creation of an optical tweezer array of single ultracold CaF molecules. By utilizing light-induced collisions during the laser cooling process, we trap single molecules. The high densities attained inside the tweezer traps have also enabled us to observe in the absence of light molecule-molecule collisions of laser cooled molecules for the first time.
Calcium monofluoride (CaF) molecules are loaded into an optical dipole trap (ODT) and subsequently laser cooled within the trap. Starting with magneto-optical trapping, we sub-Doppler cool CaF and then load 150(30) CaF molecules into an ODT. Enhanced loading by a factor of five is obtained when sub-Doppler cooling light and trapping light are on simultaneously. For trapped molecules, we directly observe efficient sub-Doppler cooling to a temperature of 60(5) µK. The trapped molecular density of 8(2) × 10 7 cm −3 is an order of magnitude greater than in the initial sub-Doppler cooled sample. The trap lifetime of 750(40) ms is dominated by background gas collisions.
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