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在磁性原子气体中，偶极弛豫过程将系统的自旋与动能自由度耦合，从而实现体系动能向塞曼能的转化. 利用光泵浦过程，可以将偶极弛豫至高自旋态的原子重新泵浦回基态，实现持续的冷却循环，有效降低体系温度. 由于单次冷却循环中移除的能量远大于散射光子能量，这种退磁冷却方案显著提升了冷却效率并减少了原子损失. 本文通过建立结合偶极弛豫与光泵浦过程的态耦合方程，对镝原子的退磁冷却进行了理论建模与计算，研究了相关实验参数对冷却效率及冷却极限温度的影响，确定了实现镝原子玻色-爱因斯坦凝聚的关键实验参数范围和技术指标要求. 结果表明，在最优实验参数下，退磁冷却可以在亚秒时间内直接制备大原子数的镝原子玻色-爱因斯坦凝聚，其冷却效率比传统蒸发冷却高一个数量级.In magnetic atomic gases, the dipolar relaxation process couples the system's spin and kinetic degrees of freedom, facilitating the conversion of kinetic energy into Zeeman energy. By utilizing optical pumping, atoms transferred to high spin states can be repumped to the ground state, thereby achieving a continuous cooling cycle and effectively lowering the system's temperature. As the energy removed in a single cooling cycle is much larger than the energy of scattered photons, this demagnetization cooling scheme significantly enhances cooling efficiency and reduces atomic loss. In this work, we establish state-coupled equations that incorporate dipolar relaxation and optical pumping to analyze the demagnetization cooling process, modeling the evolution of atom number and temperature during the cooling of 164Dy atoms. We develope a strategy to generate an optimal magnetic field waveform by maximizing the demagnetization rate. Base on this strategy, we investigate the influence of crucial experimental parameters on demagnetization cooling and determine their specific ranges for producing large atom number of BEC, including the optical dipole trap frequency, as well as the intensity and polarization purity of the optical pumping light. The results indicate that not only can demagnetization cooling achieve an efficiency of χ≈ 44.92, an order of magnitude higher than traditional evaporative cooling, but it also enables the direct preparation of a large number of dysprosium BEC within sub-second timescales, reducing the cooling time by an order of magnitude compared to conventional methods for dysprosium atoms.
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Keywords:
- magnetic atoms /
- demagnetization cooling /
- dipolar relaxation /
- optical pumping /
- Bose-Einstein condensate
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