臺灣博碩士論文加值系統

　 本論文將介紹銣87原子的玻色-愛因斯坦凝結體之實現過程，以直接又準確的方式量測凝結體中原子的數量，並且研究在玻色凝結體中電磁波引發透明的現象。 　 我們以雙磁光陷阱進行實驗，經過40秒的載入過程，可在第二個磁光陷阱中獲得 1.3×109 個低溫原子，再經過38秒的蒸發式降溫後，觀察到玻色-愛因斯坦凝結的現象，此時凝結體中原子數量為 6.2×104 個，相變溫度為 250 nK。 　 我們利用光抽運法準確地決定玻色凝結體中原子的數量，這個方法與光的頻率、強度和偏極都無關，只與被吸收的光子數有關，因此量測上造成的擾動也大大的減低，是一個可信度很高的量測方式，並且可以決定出只有幾千顆原子數的玻色凝結體。 　 我們再利用已實現的玻色凝結體來研究電磁波引發透明的現象。首先在低溫下進行電磁波引發透明的試驗，經由量測到的光譜中得到雙光子共振頻率，再利用既有的技術，在玻色凝結體中也得到一樣的結果。由於研究玻色凝結體的電磁波引發透明效應是經過一段自由擴散時間後所量測的，此時玻色凝結體的光學密度已降低至1左右，這條件對光存取實驗來講是不足夠的。下一階段，我們將利用光陷阱抓住玻色凝結體以保存凝結體的高光學密度特性，繼續進行電磁波引發透明和光存取的研究。

Contents 1 Introduction 4 1.1 History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2 The Double-MOT BEC System 6 2.1 Theoretical Discussions . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.1.1 Doppler Cooling . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.1.2 Magneto-Optical Trap . . . . . . . . . . . . . . . . . . . . . 10 2.1.3 Polarization Gradient Cooling . . . . . . . . . . . . . . . . . 11 2.1.4 Optical Pumping . . . . . . . . . . . . . . . . . . . . . . . . 14 2.1.5 Time-Averaged Orbiting Potential Trap . . . . . . . . . . . 15 2.1.6 Evaporative Cooling . . . . . . . . . . . . . . . . . . . . . . 17 2.1.7 Imaging Method . . . . . . . . . . . . . . . . . . . . . . . . 17 2.2 Vacuum System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.2.1 The Chamber of MOT1 . . . . . . . . . . . . . . . . . . . . 19 2.2.2 The Glass Cell of MOT2 . . . . . . . . . . . . . . . . . . . . 19 2.2.3 Transfer Tube . . . . . . . . . . . . . . . . . . . . . . . . . . 20 2.2.4 Rb Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.2.5 Pumping Process . . . . . . . . . . . . . . . . . . . . . . . . 22 2.3 Laser System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 2.3.1 External Cavity Diode Laser . . . . . . . . . . . . . . . . . . 24 2.3.2 Trapping Laser . . . . . . . . . . . . . . . . . . . . . . . . . 25 2.3.3 Master Oscillator Power Amplification System . . . . . . . . 25 2.3.4 Pushing Laser . . . . . . . . . . . . . . . . . . . . . . . . . . 27 2.3.5 Repumping Laser . . . . . . . . . . . . . . . . . . . . . . . . 29 1 2.4 Automatic Program Controlling System . . . . . . . . . . . . . . . 29 2.5 The Design of Magnetic Fields . . . . . . . . . . . . . . . . . . . . . 31 2.5.1 MOT1 Quadrupole Coil . . . . . . . . . . . . . . . . . . . . 32 2.5.2 MOT2 Quadrupole Coil . . . . . . . . . . . . . . . . . . . . 32 2.5.3 MOT2 Compensation Coils . . . . . . . . . . . . . . . . . . 34 2.5.4 Time-Averaged Orbiting Potential Trap . . . . . . . . . . . 34 2.6 Image System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 2.6.1 Fluorescence Detection . . . . . . . . . . . . . . . . . . . . . 36 2.6.2 Absorption Imaging . . . . . . . . . . . . . . . . . . . . . . . 36 2.7 Cooling Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 2.7.1 Collecting Cool Atoms . . . . . . . . . . . . . . . . . . . . . 37 2.7.2 Polarization Gradient Cooling . . . . . . . . . . . . . . . . . 39 2.7.3 Loading the B-trap . . . . . . . . . . . . . . . . . . . . . . . 39 2.7.4 Evaporative Cooling . . . . . . . . . . . . . . . . . . . . . . 40 2.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 3 Determination of the Atom Number in a Bose Condensate 45 3.1 Principle of Optical Pumping Method . . . . . . . . . . . . . . . . . 46 3.2 Experimental Results and Discussions . . . . . . . . . . . . . . . . . 47 3.2.1 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . 47 3.2.2 Results of Optical Pumping . . . . . . . . . . . . . . . . . . 47 3.2.3 Comparing AI with OP . . . . . . . . . . . . . . . . . . . . 50 3.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 4 EIT Spectrum in Bose Condensates 56 4.1 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 4.2 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . 59 4.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 5 Conclusions and Prospects 68 6 Appendix A : LabVIEW Program 74 7 Appendix B : Photon Detector 79 8 Appendix C : Timing Sequence of Optical Pumping Measurement 80

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