We report on the efficient gray molasses cooling of sodium atoms using the D2 optical transition at 589.1 nm. Thanks to the hyperfine split about between and in the excited state , this atomic transition is effective for the gray molasses cooling mechanism. Using this cooling technique, the atomic sample in F = 2 ground manifold is cooled from to in 3.5 ms. We observe that the loading efficiency into magnetic trap is increased due to the lower temperature and high phase space density of atomic cloud after gray molasses. This technique offers a promising route for the fast cooling of the sodium atoms in the F = 2 state.

We report on the production of Bose–Einstein condensates of sodium atoms in the hyperfine state | F = 2 , m F = 2 ⟩ in a crossed optical dipole trap using D 2 gray molasses. We use the gray molasses sub-Doppler cooling technique to obtain an atomic sample of 3 × 10 8 at 56 µK. After the radio frequency (RF) evaporation cooling in an optically plugged magnetic trap, we transfer the atoms sample of 2.5 × 10 6 at 5.7 µK to a crossed optical dipole trap where a pure condensate with an atom number of 2 × 10 5 and lifetime of 6.3 s is obtained by further evaporation. We compare the cooling process of sodium atoms in the | 2 , 2 ⟩ and the | 1 , 1 ⟩ states by evaporation in the optical trap, and also observe the different three-body loss rates by the lifetime measurement.

It is helpful to make full use of the laboratory space by simplifying the cold atom experimental system, especially in the area of aerospace and precision measurement. We present a two-dimensional magneto-optical trap (2DMOT) for sodium atoms, whose magnetic field is produced by four sets of permanent magnets, and the residual field in the vertical direction is used for a Zeeman slower. The atoms are cooled and trapped in a 2DMOT which provides a highly efficient atomic flux for three-dimensional magneto-optical trap (3DMOT) in a high-vacuum chamber. The maximum 3DMOT loading rate is measured to be 2.3 × 10⁹/s by optimizing the parameters of the Zeeman slower and the 2DMOT. The atom number trapped in 3DMOT is 6.2 × 10⁹. The 2DMOT designed by using permanent magnets has the property of compact structure and simple size, which can be used to cool and trap other neutral atoms.

We experimentally observe the collective excitation (called surface-mode excitation) of Bose-Einstein condensate (BEC) of $^{23}$Na by ramping the external magnetic field across the high-partial wave magnetic Feshbach resonance corresponding to vary the atomic interaction. We check the collective surface mode excitation of $|1, 1\rangle$ state for the three d-wave and three g-wave Feshbach resonances below 600 G and find that only two d-wave resonances present the strong excitation, another d-wave resonance only creates a weak excitation, and all g-wave resonances do not, which reflects the strength of these magnetic Feshbach resonances. For the collective excitation, the excitation of surface modes along the axial weak-confinement and radial strong-confinement of optical dipole trap shows different characteristics. We also study the lifetime of the collective oscillation by measuring the damping rate of the oscillation amplitude, which is caused by the mechanisms of dephasing effect and collisional relaxation. This excitation method gives us a new tool for investigating the properties of ultracold quantum gases without changing the trap frequencies.