銣87原子之玻色-愛因斯坦凝聚體在環形光阱的製備

The Production of 87Rb Bose-Einstein Condensates in a Toroidal Trap

魏宏吉(Hung-Ji Wei)

指導教授 ： 劉國平

共同指導教授 ： 林育如

國立臺灣大學/理學院/物理學研究所/碩士(2016年)

https://doi.org/10.6342/NTU201602457

摘要

我們在紅調變與藍調變的環形光阱中產生銣87原子的玻色-愛因斯坦凝聚體。在實驗中，我們以光罩產生紅調變與藍調變的環形光，藉由結合一道在垂直方向聚焦的扁平高斯光與一道垂直行進的環形光，我們產生環形光阱。實驗程序上，我們首先以磁光阱(magneto-optical trap)收集原子並進行亞都卜勒雷射冷卻(sub-Dopper laser cooling)，接著將原子轉移到由磁阱與交叉光偶極阱(crossed optical dipole trap)組成的位能阱中進行蒸發冷卻，並更進一步由磁場與重力的位能梯度達成蒸發冷卻。最後我們將原子分別轉移到紅調變與藍調變的環形光阱中，在兩種光阱下都得到原子數N=3×10^5的玻色-愛因斯坦凝聚體，與在一般光耦極阱得到的原子數相同。我們也觀察到，當內能主導下的化學位能與光阱位能相接近的情況下，原子密度分布在藍調變環形光阱中會比在紅調變環形光阱內更均勻，而原因是藍調變光阱在沿方位角方向的位能變化極小。另外，在兩種光阱中，原子生命期皆為9秒。在未來，我們將在此環形光阱中加入一道雷射光與另一道帶有軌道角動量的拉蓋爾-高斯光(Laguerre-Gaussian beam)來產生拉曼耦合作用，使原子耦合為綴飾態(dressed state)並產生等效規範場(synthetic vector gauge potentials)。

關鍵字

玻色-愛因斯坦凝聚體 ； 雷射冷卻 ； 磁光阱 ； 光耦極阱 ； 環形光 ； 環形光阱

並列摘要

We produce Bose-Einstein condensates (BECs) of Rubidium 87 atoms in both red-detuned and blue-detuned optical ring trap, where the ring-shaped beams are generated by using intensity masks. The intersection of a sheet beam which tightly focused vertically and a ring beam propagating along the vertical direction then forms the ring trap. In our experimental procedure, we first collect and trap atoms in a magneto-optical trap (MOT) and perform sub-Doppler laser cooling, and transfer the atoms to the hybrid potential of quadrupole magnetic trap and crossed optical dipole trap. We then perform forced dipole evaporative cooling and then a following evaporation using a gradient potential as a combination of the gravity and magnetic gradient. Finally, we transfer the cold atoms to the red-detuned ring trap and blue-detuned ring trap, respectively, and achieved BECs with N=3×10^5 atoms in both cases, which is the same as that produced in the dipole trap alone. The BEC density profile in the blue-detuned ring trap is smoother than that in the red-detuned ring trap for comparable interaction-dominated chemical potential. This is owing to the much smaller azimuthal potential variations for blue-detuned trap. The BEC lifetime is 9 s in both ring traps. In the future, we will adopt a Gaussian beam and a Laguerre-Gaussian beam which carries orbital angular momentum to load atoms in the ring trap into a Raman dressed state, and create synthetic vector gauge potentials.

並列關鍵字

Bose-Einstein condensate ； laser cooling ； magneto-optical trap ； optical dipole trap ； ring beam ； optical ring trap

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