【作者】 王继成；

【导师】 刘树田；

【作者基本信息】 哈尔滨工业大学 ， 光学， 2011， 博士

【摘要】 激光冷却与囚禁技术的发展,为原子、分子与光物理的研究打开了新的篇章。超冷原子碰撞作为冷原子物理研究中的前沿课题之一受到了人们极大的关注。在超冷原子碰撞中,原子的碰撞截面研究是一个热门的研究课题。粒子的碰撞截面的大小反映了粒子发生碰撞的可能性大小。通过研究粒子的碰撞截面,可以获得原子冷却及BEC实验中被捕获粒子的数目、粒子的损失率、粒子的两体及多体碰撞参数、冷原子势阱深度等重要信息,对超冷原子物理研究有十分重要的作用。本论文旨在研究磁光阱与磁阱中超冷Rb原子与背景气体(Ar, He)碰撞实验过程,提出一种测量冷原子碰撞截面的新技术。对Rb冷原子与背景气体碰撞展开实验及理论研究。论文的主要研究内容如下:提出在磁光阱和磁阱中利用超冷87Rb原子与室温下背景气体40Ar碰撞测量完全碰撞截面的新技术。利用该技术在磁光阱及磁阱中可以精确测量不同背景气体密度下的超冷Rb原子的损失率、碰撞截面。可以将此技术作为标准方法测量超冷原子的碰撞截面。磁光阱与磁阱的系统的是实现碰撞截面测量实验重要的环节。实验装置包括真空系统、激光器系统及激光稳频系统和Rb冷原子源三个主要组成部分。实验中通过计算机软件控制来实现冷却激光的打开或关闭,简单的实现磁光阱与磁阱的切换。利用冷原子碰撞截面测量技术,在磁光阱及磁阱中,对Rb原子两种同位素85Rb和87Rb与惰性气体Ar与He碰撞进行研究。实验研究发现,Rb冷原子与惰性气体的碰撞损失率、碰撞截面在磁光阱与磁阱中有很大差别。利用原子碰撞物理学理论,通过分步法拟合法计算碰撞截面、平均速度损失率与L-J势函数系数、势阱深度、碰撞速度、碰撞能量等参量的演化关系;通过理论计算与实验测量的碰撞截面、平均速度损失率值比较,发现理论与实验值基本吻合,并给出理论计算的碰撞截面、平均速度损失率与势阱深度的关系,可以得到由于实验磁场条件限制不能达到势阱深度下的碰撞截面或平均速度损失率值。利用理论计算平均速度损失率与势阱深度的关系,提出利用磁光阱与磁阱中87Rb冷原子与室温40Ar背景气体之间碰撞测量势阱深度的新方法。与在光阱利用激光催化测量Rb冷原子确定势阱深度的方法相比,该方法操作更简单,只需要测量Rb原子与背景气体之间一阶碰撞损失率Γ,避免测量冷原子间碰撞损失率β时对原子密度要求较高的影响,测量原子密度很低条件下的势阱深度;该方法可以在磁光阱及磁阱中测量势阱深度,扩大了势阱深度测量范围。最后,腔量子电动力学是冷原子物理的前沿领域。研究了k光子Jaynes-Cummings腔QED模型与运动原子相互作用中的熵相互关系及纠缠特性。发现原子与光场之间具有熵交换特性。讨论了原子运动、光子数和场模结构等因素对原子与光场熵相互关系的影响。此外,讨论了原子与场系统熵交换与纠缠之间的关系。更多还原

【Abstract】 Ultracold atomic collisional physics is a promsing field in ultracold physics, scientists play more and more attention to this area because it is significant and has the possibility of broad applications in future. The atom collisional cross section is a more popular research topic in the field of ultracold atom collision physics. In nuclear and particle physics, the concept of cross section is used to express the likelihood of interaction between particles. The informations of the trapped atom numbers of laser cooling or BEC experiments, particle loss rate, collision parameters, trap depth of cold atoms can be achieved by measured collision cross section of cold atoms. It is very important to the research on ultracold atomic physics. In this dissertation, we study the experiments of ultracold Rb atom collided with background Ar or He gas using magneto-optic and magnetic traps. A new technique to measure collision loss rate and absolute collision cross sections is proposed. An overview of both experimental and theoretical results for the case of trapped Rb and background argon or helium gas will be given. The research work has been summarized in detail as follows.We present a new technique to measure the absolute total collision cross sections for a room-temperature background gas of 40Ar using laser cooled 87Rb atoms confined in either a magneto-optic or a magnetic quadrupole trap. By using this method, loss rate of trapped atoms and the total cross section can be accurately achieved from knowledge of the background gas density. This technique can be a normative method to acquire collision cross sections of ultracold atoms with other background gases in the further work. Building up the MOT and magnetic trap is the most important task in this experiment work. Three requisite instruments are involved in this experiment, which are vacuum system, laser light systems and Rb injection system. Using software control system can turn on and off lasers to simply transfer MOT to magnetic trap.By using this new technique, we measure 85Rb or 87Rb collided with room-temperature background rgon or helium gas in the MOT and magnetic trap. The loss rates from the magneto-optic trap (MOT) and the pure magnetic trap are compared and show significant differences. The initial discussion focuses on a theoretical overview of the principles involved in atom collisional physics fields. Finally, an overview of both experimental and theoretical results including cross sections and loss rates for the case of trapped 85Rb or 87Rb and background Ar or He gas will be given. These results suggest that this theory may be a better tool for measuring total elastic collision cross section on arbitrary trap depth. Then, we present a new method for determining the trap depth of an atomic or molecular trap of any type and any depth. This method relies on measurements of the trap loss rate induced by elastic collisions of ultracold 87Rb atoms with room temperature background 40Ar gases. We compare this method with an independent technique that relies on measurements of atom loss rates during optical excitation of colliding pairs to a repulsive molecular state. The main advantage of the method presented here is its simplicity and applicability to traps of any type requiring only knowledge of the background gas pressure between the trapped particles and the background gas particles. Another advantage is that the technique is applicable to any type of traps, including the optical and magnetic traps, and at extremely low densities where intra-trap collisions are rare.Finally, cavity quantum electrodynamics is a promising research field of the cold atom physics. The entropy correlation and entanglement of a moving atom interacting with k-photon Jaynes-Cummings model are investigated. Entropy exchange, which is a form of anti-correlated behavior between atomic and field subsystems, is explored. Analytical results represents that the atomic motion, transition number k of field and field-mode structure show some influence on entropy exchange. Moreover, the relationship between entropy correlations and entanglement is also discussed.更多还原