銣原子與銣分子之超冷碰撞研究

Ultracold collisions of rubidium atoms and molecules

陳俊任(Jun-Ren Chen)

指導教授 ： 劉怡維

國立清華大學/理學院/物理學系/博士(2016年)

摘要

在此論文中，我們利用所謂的光結合法(photo-association)來產生銣分子並發展出一套方法來偵測他們；透過捕捉於光偶極阱中的原子與分子的碰撞，我們得以偵測到這些基態分子的訊號。
在銣原子(85Rb)磁光陷阱原子團中，透過上述的光結合過程將可以組成激發態的超冷銣分子。 同時，透過所謂的共振耦合效應(resonance coupling effect)將可大幅增加上述已生成的激發態分子自發銳變至基態的數量。這些生成的基態銣分子將同時和磁光陷阱中剩餘未結合的銣原子一併載入一個交叉形式的光偶極阱中。透過光結合過程所產生的基態分子對光偶極阱中的原子團所造成的額外碰撞損耗，將可以用來估計光偶極阱中分子的數目和密度，分別為Nm=44-110×10^3以及nm>5.2×10^11 cm^(-3)。
為了改善此偵測方法的靈敏度，我們將需要更長的原子團生命期，而此目標可以透過將原子團轉移至另一具備超高真空度的環境來達成。在實驗上，原子在空間上的轉移是透過一個架設在線性磁軌上的磁位能阱來實現。同時，在此超高真空度的環境裡，原子的生命期獲得了顯著的延長，而原子和分子的碰撞效應將因此而較原子與背景殘留氣體的碰撞效應敏感。
我們實驗系統的許多特性得以透過成功產生銣原子(87Rb)的玻色‧愛因斯坦凝結體(BEC)來檢驗。此實驗裝置的主要配置結合了單一光束的光偶極阱與提供軸向束縛力的微弱磁位能阱。最終，我們的系統產生約由6.3×10^5個原子所組成的BEC。同時，在將來的實驗上此玻色‧愛因斯坦凝結體將用在和應冷卻(sympathetic cooling)鉀原子，鉀分子以及銣分子上。

關鍵字

玻色愛因斯坦 ； 超冷碰撞 ； 銣 ； 光結合 ； 冷分子 ； 磁轉移 ； 光偶極阱 ； 磁位能阱 ； 超冷原子

並列摘要

This thesis studies the formation of rubidium molecules by photoassociation (PA) method and develops a method for detecting the formed ground state molecules using collisions of atoms and molecules in an optical dipole trap.
In the magneto-optical trap of 85Rb, ultracold rubidium molecules, in the excited-electronic state, were produced using the photoassociation process. With the help of resonance coupling effect, the number of molecules in the ground-electronic state which decay spontaneously from the excited molecular state can be enhanced. The formed ground state molecules and the remaining atoms in the trap were simultaneously loaded into a crossed optical dipole trap. Addition to the background collision losses, the extra losses of 85Rb atoms due to the photoassociated molecules in the optical trap can then be used to estimate the number and density of molecules in the trap, which is Nm=44-110×10^3以及nm>5.2×10^11 cm^(-3).
In order to improve the sensitivity of our detecting method, a longer trapping lifetime is needed. It was achieved by transporting atoms to an ultra-high vacuum chamber. In our apparatus, such a transportation of atoms was realized using a magnetic trap settled on a linear motor track. In the ultra-high vacuum chamber, the atomic lifetime is extended signi_cantly, and the collisions between atoms and molecules become more sensitive than the background residual gas collision.
Several important characteristics of our apparatus was verified by producing the
Bose-Einstein condensate (BEC) of 87Rb in a hybrid configuration: a single beam optical dipole trap within axial confinement supported by a weak magnetic trap. A pure condensate with 6.3×10^5 atoms are formed in this hybrid trap. This 87Rb BEC can be a refrigerant for the future sympathetic cooling with K, Rb2 and K2.

並列關鍵字

Bose-Einstein Condensate ； ultracold collision ； Rubidium ； photoassociation ； cold molecule ； magnetic transfer ； optical dipole trap ； quadrupole trap ； ultracold atom

參考文獻

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