Summary: Here we report the experimental realization of a vortex matter-wave interferometer by coherently transferring the optical angular momentum to an ultracold Bose condensate. We use the angular interference technique to measure the relative phase of two vortex states. For a lossless interferometer with atoms only populating two spin states, the difference between the relative phases in the two spin states is locked to $\pi$. We also prove the robustness of this out-of-phase relation, not sensitive to the angular-momentum difference between two vortex states, constituent of Raman optical fields and expansion of the condensate. The experimental results agree well with the calculation from the unitary evolution of wave packet in quantum mechanics. This work opens a new way to build a quantum sensor based on the vortex matter-wave interference.(Paper, Link)

Summary: We experimentally and theoretically characterize the temporal rotation and radial twist of the interference pattern of a vortex beam with its conjugate copy. To quantitatively study the temporal rotation and radial twist, we controllably modify the conjugate beam to obtain a frequency or wavefront curvature difference using a movable Mach–Zehnder interferometer. The effects of the physical parameters (i.e., the topological charge, frequency difference and wavefront curvature difference of the vortex beams) on the temporal rotation as well as radial twist are systematically explored. We further measure two parameters, the rotation velocity and twist coefficient , respectively, to characterize the degree of the temporal rotation and radial twist of the interference pattern. The theory of the interference model on vortex beams has good agreement with the experimental results. (Paper, Link)

Summary: We observe characteristic atomic behaviors in the Bose–Einstein-condensation-Bardeen–Cooper–Schrieffer (BEC-BCS) crossover, by accurately tuning the magnetic field across the Feshbach resonance of lithium atoms. The magnetic field is calibrated by measuring the Zeeman shift of the optical transition. A non-monotonic anisotropic expansion is observed across the Feshbach resonance. The density distribution is explored in different interacting regimes, where a condensate of diatomic molecules forms in the BEC limit with the indication of a bimodal distribution. We also measure the three-body recombination atom loss in the BEC-BCS crossover, and find that the magnetic field of the maximum atom loss is in the BEC limit and gets closer to the Feshbach resonance when decreasing the atom temperature, which agrees with previous experiments and theoretical prediction. (Paper, Link)

Summary: We report the experimental production of degenerate Fermi gases of ⁶Li atoms in an optical dipole trap. The gray-molasses technique is carried out to decrease the atomic temperature to 57 nK, which facilitates the efficient loading of cold atoms into the optical dipole trap. The Fermi degeneracy is achieved by evaporative cooling of a two-spin mixture of 6Li atoms on the Feshbach resonance. The degenerate atom number per spin is 3.5*10⁴, and the reduced temperature T/T_Fis as low as 0.1, where T_Fis the Fermi temperature of the non-interacting Fermi gas. We also observe the anisotropic expansion of the atom cloud in the strongly interacting regime. (Paper, Link)

Summary: We experimentally and theoretically observe the expansion behaviors of a spherical Bose–Einstein condensate. A rubidium condensate is produced in an isotropic optical dipole trap with an asphericity of 0.037. We measure the variation of the condensate size in the expansion process after switching off the trap. The free expansion of the condensate is isotropic, which is different from that of the condensate usually produced in the anisotropic trap. We derive an analytic solution of the expansion behavior based on the spherical symmetry, allowing a quantitative comparison with the experimental measurement. The interaction energy of the condensate is gradually converted into the kinetic energy during the expansion and after a long time the kinetic energy saturates at a constant value. We obtain the interaction energy of the condensate in the trap by probing the long-time expansion velocity, which agrees with the theoretical calculation. (Paper, Link), [Suggested by Edotors]

Summary: We experimentally realize the spin-orbital-angular-momentum (SOAM) coupling by using a pair of Gaussian and Laguerre-Gaussian laser beams, and map out the ground-state phase diagram. The phase transition is demonstrated to be of the first order. We observe the hysteresis loop associated with the first-order phase transition. The interatomic interaction effect on the phase transition is also elucidated. (Paper, Link). [Research Highlights in Science Foundation in China 27: 12 (2019)]

Summary: We experimentally observe the dynamic evolution of atoms in the evaporative cooling, by in-situ imaging the plugged hole of ultracold atoms. We probe the variation of the atomic temperature and width versus the radio frequency in the evaporative cooling. Both the behaviors are in good agreement with the calculation of the trapping potential dressed by the rf signal above the threshold temperature, while deviating from the calculation near the phase transition. (Paper, Link)

Summary: We extend the contact theory to the spin-orbit-coupled (SOC) Fermi system. New scattering paramters, besides the s- and p-wave scattering length (volume), are required due to the SOC effect.  The energy adiabatic relation and large-momentum distrituion are obtained for the coupled system. (Paper, Link)

Summary: We experimentally produce the rubidium Bose–Einstein condensate in an optically plugged magnetic quadrupole trap. The atom number of the condensate is 1.2(0.4) × 10⁵ and the temperature is below 100 nK. We also study characteristic behaviors of the condensate, such as phase space density, condensate fraction and anisotropic expansion.

(Paper, Link)

Summary: We experimentally and theoretically demonstrate the enhancement of 6Li trapping efficiency in a three-dimensional magneto-optical trap (3D MOT) by using the multiple-sideband cooling in a two-dimensional magneto-optical trap (2D MOT). The number of trapped atoms in the 3D MOT is 6.0 × 10⁸, which is higher by a factor of 4 than in the case of single-frequency cooling. We have investigated the dependence of atom number on laser detuning, and our experimental result agrees well with the prediction of a simple two-level model. (Paper, Link)

Summary: We propose a new method, using the magnetic vector, to manipulate the atomic interaction. The p-wave interaction depends not only on the magnitude but also on the direction of the magnetic field. The anisotropic scattering property of the p-wave interaction is demonstrated. (Paper, Link)

Summary: We have experimentally studied multiple side-band generation for two-frequency components injected into a tapered amplifier (TA) and demonstrated its effects on atomic laser cooling. A heterodyne frequency-beat measurement and a Fabry–Perot interferometer have been applied to analyze the side-band generation with different experimental parameters. The side-band generation with a small frequency difference has a significant effect on the number of trapped atoms.

(Paper, Link)