强磁场中自旋极化的冷钠原子
Spin-Polarizing Cold Sodium Atoms in a Strong Magnetic Field
摘要：
用于产生玻色-爱因斯坦凝聚体的蒸发冷却的效率很大程度上取决于蒸发开始时的粒子数量。通过用大量原子填充磁光阱并随后尽可能有效地将这些原子转移到磁阱，可以达到高效率。在我们的例子中（对于钠），这个效率被限制在1/3，因为在俘获过程中使用的F = 1态的磁子态是均等的。这个限制可以通过在转移之前对样品进行自旋极化来克服。然而，对于钠原子，当在小磁场中进行时，由于大量的光跃迁与高的光密度相结合，改善非常小。本文描述了钠原子在强磁场中的自旋极化。传输效率提高了2倍。高磁场使得该过程也更鲁棒地抵抗磁场、激光频率和激光束的偏振的变化。
英文摘要：
The efficiency of evaporative cooling, which is used for the creation of a Bose Einstein condensate, depends strongly on the number of particles at the start of the evaporation. A high efficiency can be reached by filling the magneto-optical trap with a large number of atoms and subsequently transferring these atoms to the magnetic trap as efficiently as possible. In our case (for sodium) this efficiency is limited to 1/3, because the magnetic substates of the F = 1 state, which is used in the trapping process, are equally populated. This limit can be overcome by spin-polarizing the sample before the transfer. For sodium atoms, however, the improvement is very small when it is done in a small magnetic field due to the large number of optical transitions in combination with the high optical density. In this article we describe spin-polarizing sodium atoms in a high magnetic field. The transfer efficiency is increased by a factor of 2. The high magnetic field makes the process also more robust against variations in the magnetic field, the laser frequency and the polarization of the laser beam.
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