鉀-39之磁費許巴赫共振

Abstract

本實驗完成全光學式(all-optical configuration) 鉀-39原子之玻色-愛因斯坦凝結(Bose-Einstein condensates) 實驗之前期架設，並且取得該原子於基態|F = 1>各磁量子數之磁費許巴赫共振譜線(magnetic Feshbach resonances)。實驗裝置包含塞曼減速管(Zeeman slower)、磁光阱(magneto-optical trap, MOT)、光阱(optical dipole trap, ODT)，本實驗分析並優化實驗條件。配合塞曼減速管，磁光阱的載入速率增加七倍，其載入速率為1.6秒，三秒約有10^8顆原子。經過次都卜勒冷卻(sub-Doppler cooling)，於磁光阱之原子的溫度從2 mK降溫至80 K。目前光阱已成功載入10^6顆原子。因為鉀-39 具有吸引的原子交互作用力，不利於進一步之相空間提升，因此採取磁費許巴赫共振以調整原子散射態(scattering state) 與分子束縛態(bound state) 之耦合(coupling)，進而改變原子交互作用力。目前磁場可高達近300 G。由於本實驗原子團製備過程為全光學式，其保留了各磁量子數之原子，因此將實驗獲得之共振磁場譜線與理論對照，已取得基態|F = 1>純化之磁量子數――mF = (1; 1) 與mF = (0; 0) 之費許巴赫共振譜線。

This study has completed initial set-up of potassium-39 Bose-Einstein condensates (BEC) and demonstrated the magnetic Feshbach resonances of atoms prepared by all-optical configuration. The experiment starts with loading a magneto-optical trap (MOT) from a Zeeman slower. Subsequently the laser-cooled atoms are then loaded into an optical dipole trap (ODT). With the slower, the loading rate increases by nearly 30 times. The MOT loading time constant achieves 1.6 s and the saturated atom number is equivalent to 10^8 at a temperature of 2 mK. After sub-Doppler cooling, the MOT temperature reaches 80 K and 10^6 atoms are successfully loaded in ODT. Since potassium-39 inherently has attractive interatomic interaction, which is detrimental to phase-space density enhancement of the atoms, Feshbach resonances is implemented to tune the coupling of a scattering state and a bound state of two colliding atoms. With cold atoms, which preserves Zeeman sub-levels states, two scattering channels with pure polarization–mF = (1,1) and mF = (0,0) of the F = 1 manifold have been observed. All information is enclosed in detail in this thesis.