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Journal of the Optical Society of America B

Production of 23Na Bose–Einstein condensates in the F = 2 state using D2 gray molasses

Zhenlian Shi, Zi‐Liang Li, Pengjun Wang, Khan Sadiq Nawaz, Liangchao Chen, Zengming Meng, Lianghui Huang, Jing Zhang

Published Mar 2, 2021• 4 citations
Publisher

Abstract

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.

DOI
10.1364/josab.414781

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We use D1{D}_{1}D1​ gray molasses to achieve Bose-Einstein condensation of a large number of 41K^{41}\mathrm{K}41K atoms in an optical dipole trap. By combining a specific configuration of a compressed magneto-optical trap with D1{D}_{1}D1​ gray molasses, we obtain a cold sample of $2.4\ifmmode\times\else\texttimes\fi{}{10}^{9}$ atoms with a temperature as low as 42 $\ensuremath{\mu}\mathrm{K}$. After magnetically transferring the atoms into the final glass cell, we perform a two-stage evaporative cooling. A condensate with up to $1.2\ifmmode\times\else\texttimes\fi{}{10}^{6}$ atoms in the lowest Zeeman state $|F=1,{m}_{F}=1\ensuremath{\rangle}$ is achieved in the optical dipole trap. Furthermore, we observe two narrow Feshbach resonances in the lowest hyperfine channel, which are in good agreement with theoretical predictions.
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A rapid atomic beam of rubidium (87Rb) is produced by two-dimensional magneto-optical trap (2D MOT), and then trapped by three-dimensional magneto-optical trap (3D MOT) with high vacuum for further cooling. After a process of optical molasses cooling, atoms are reloaded into a magnetic trap, where radio frequency (RF) evaporation cooling is implemented. The precooled atoms in the magnetic trap are then transferred into a far detuning optical dipole trap, where Bose-Einstein condensate (BEC) appears by further evaporation cooling. The 3D MOT is loaded to its maximum within 25 s and then BEC is prepared in 16 s. Due to the linear intensity of magnetic trap, the frequency can be scanned fast in the RF evaporation cooling process. In our experiment, the frequency scans from 39 MHz to 15 MHz in 6 s and then scans to 2 MHz in 5 s. The number of atoms in 3D MOT is about 11010, and there are 5105 atoms in the BEC after a succession of cooling processes. To optimize the performances of 2D MOT, a special light path is constructed. And prisms with high reflectivity are used to reduce the imbalance between opposite propagating cooling +beams. Furthermore, quarter-wave plates are used to keep the polarization state of the cooling beam when reflected by prisms or mirrors. The atoms are cooled to a temperature about 15 K in the magnetic trap by RF evaporation. In such a low temperature, the loss of magnetic trap (Majorana loss) will prevent the atoms from reaching a high density, and the atoms cannot be cooled further. To reduce the loss rate of the magnetic trap, the far blue detuning light (532 nm, 18 W) is added to plug the zero point of the magnetic trap. In the optically plugged magnetic trap, atoms with high density are cooled down enough, which gives a good start for the loading of optical dipole trap.
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