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题名	参量冷却与mini势阱的理论和实验研究
作者	张鹏飞
学位类别	博士
答辩日期	2008
授予单位	中国科学院上海光学精密机械研究所
导师	王育竹
关键词	磁四极阱 参量冷却 直接模拟蒙特卡罗 mini磁阱 高频导引
其他题名	Theoretical and Experimental Study on Parametric Cooling and Mini-Trap
中文摘要	本学位论文的工作分成两个部分。第一部分研究了磁四极阱中原子的参量冷却，第二部分研究了中性原子的mini势阱和高频导引。 由于磁四极阱是非简谐阱，被囚禁的原子蕴涵着极其丰富的非线性物理现象。本学位论文展示了，利用参量激发，能量选择地搬走磁阱中的热原子，是一种新的冷却原子的方法。采用直接模拟蒙特卡罗方法，我们研究了四极阱中原子温度对激发频率的依赖关系，证明了囚禁的原子在较低的激发频率处被冷却。本论文还研究了激发幅度和原子的弹性碰撞速率对冷却温度的影响，得出了一 些很重要并且很有趣的结果。为了证实理论模拟结果，我们建立了一套参量冷却实验装置，开展了相应的实验研究。本论文对我们的实验装置和实验程序进行了非常详细的介绍，并且给出了参量冷却的实验结果。实验得到的原子团温度相对于激发频率的关系曲线与数值模拟的结果是一致的。采用参量冷却技术，原子团的温度降低了10%。 根据Maxwell方程，磁场强度的空间极大值点是不存在的，所以静磁阱只能囚禁弱场俘获态(week-¯eld-seeking)的原子。本论文提出了原子射频导引的一个技术方案，该方案可以实现强场俘获态(strong-¯eld-seeking)原子的二维囚禁。为了有利于射频导引的原子装载，我们建立了国内第一套mini势阱实验装置，并且将射频导引组装到该系统中，使它们成为一个整体。本论文详细介绍了mini势阱和射频导引的原理、设计、实验平台的建立以及实验程序，并且给出了初步的实验结果。约5*107<\sup>个铷原子被腔外的磁光阱俘获，经过偏振梯度冷却后温度降低到20uK左右。激光冷却的原子光抽运到|F = 2;mF<\sub>= 2>磁子能级后被四极阱囚禁，四极阱中的原子数为2*107<\sup>。磁囚禁的原子利用另外一对四极阱线圈向下转移了28 mm。我们对转移过程进行了优化，以减少转移带来的原子团加热，有8*106<\sup>个原子被转移到了mini四极阱的中心位置。紧接着原子被mini四极阱囚禁，并被装载到mini QUIC阱中。Mini势阱囚禁的原子数目约为3*106<\sup>，温度在300uK左右。我们下一步的工作努力就是采用mini QUIC阱正下方的射频导引实现原子的二维囚禁。
英文摘要	The work described in this dissertation can be divided into two parts. The first part is concerned with the parametric cooling of atoms in a magnetic quadrupole trap. The second part describes studies of the mini-trap and radio-frequency (rf) guide for neutral atoms. Owing to the anharmonicity of the magnetic quadrupole trap, the trapped atoms reveal a rich variety of nonlinear physical phenomena. In this dissertation, energy-selective removal of hot atoms by parametric excitation is shown as a new solution for creating ultra-cold atoms. Using the Direct Simulation Monte Carlo (DSMC) method, we investigated the excitation frequency dependence of the temperature of atoms confined in a quadrupole trap, and demonstrated that the trapped atoms were cooled at lower excitation frequency. The effects of the excitation amplitude and the mean elastic rate of atoms on the cooling temperature were investigated, and some important and interesting results were obtained. To confirm the theoretical results, we established the experimental setup for parametric cooling, and carried out the corresponding experimental studies. This dissertation describes in detail our apparatus and experimental procedure, and presents the experimental results. The temperature as the function of the excitation frequency coincided with the one given by the numerical simulation method, and a 10 percent decrease in temperature was achieved in our experiment. A static magnetic field can only confine weak-field-seeking atoms because Maxwell's equations do not allow a local maximum in magnetic field magnitude. In this dissertation, a technique scheme for guiding atoms in strong-field-seeking states with radio-frequency field is proposed. To make the loading of the rf guide much easier, we established the first mini-trap setup in China, and incorporated the rf guide into this system. The principle, design, experimental procedure and the preliminary results are presented. About 5*107<\sup> rubidium atoms were captured in the magneto-optical trap (MOT) placed out of the vacuum cell, and cooled to about 20uK by the polarization gradient cooling. After optical pumping into the |F = 2;mF<\sub>= 2> state, 2*107<\sup> cold atoms were loaded into the magnetic quadrupole trap. The trapped atoms were then transferred 28 mm downwards using another pair of quadrupole coils. The transport process was optimized to minimize heating of the trapped atoms, and 8*106<\sup> atoms were transferred into the centre of the mini quadrupole trap. The transferred atoms were then confined in the mini quadrupole trap, and loaded into the mini QUIC trap. Approximately 3*106<\sup> atoms were confined in the QUIC trap, and the temperature was about 300uK. We advise that the next attempt is to realize the guiding of atoms with the rf guide placed below the mini QUIC trap.
语种	中文
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/15225]
专题	上海光学精密机械研究所_学位论文
推荐引用方式 GB/T 7714	张鹏飞. 参量冷却与mini势阱的理论和实验研究[D]. 中国科学院上海光学精密机械研究所. 2008.

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