气态玻色-爱因斯坦凝聚实验及若干理论问题研究
文献类型：学位论文
| 作者 | 付海翔 |
| 学位类别 | 博士 |
| 答辩日期 | 2003 |
| 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 | 玻色-爱因斯坦凝聚 磁势阱 时序控制程序设计 修正GP方程 坍缩延迟 光塞 光学“微外科手术” |
| 中文摘要 | 本论文研究玻色一爱因斯坦凝聚实验和理论上的几个问题。论文分成两个部分。第一部分研究BEC的实验。首先，我们讨论制备BEC的几个实验环节，包括我们提出的一种新型微势阱。然后我们从几个方面讨论中国第一个玻色一爱因斯坦凝聚实验，包括：QUIC势阱的结构、搭建和测量；时序控制程序设计；上海光机所BEC实验的过程和实验结果。论文的第二部分研究BEC理论方面的几个问题。在介绍BEC的动力学理论时，重点讨论了平均场理论框架中的几种解析方法和数值方法，并用这些方法研究了BEC的稳定性问题和BEC的激发和阻尼。然后我们研究冷原子的相互作用，内容涉及冷原子基态碰撞的特点和费米膺势、Feshbach共振，之后介绍了一种新型角动量无关的量子亏损理论，在此基础上，我们提出了一种新型修正GP方程，并用数值计算研究了它的基态能量。和蒙特卡罗结果的对比说明，该方程对GP方程有较大修正。在最后一章我们研究了相互作用可调谐的BEC动态坍缩的几个问题。首先，我们研究了实验中观察到的坍缩延迟现象。我们认为，坍缩延迟是因为凝聚体粒子数密度积累需要一定时间。数值模拟结果和实验数据吻合的较好。通过和实验过程的比较，我们注意到，实验中忽略掉的一个因素，即凝聚体坍缩开始前的形状振荡对坍缩动力学有实质性的影响，数值计算结果表明，坍缩延迟时间会随凝聚体的这个初始集合振荡而周期性的变化。其次，我们提出了用光学塞子来控制BEC的动态坍缩。我们发现当光塞强度增大到一定程度时，会诱导出一种新型拓扑结构的坍缩现象。我们详细研究了光塞对坍缩临界相互作用强度值的影响。最后，我们进一步提出把光学偶极力作为控制BEC坍缩的“微外科手术”控制 工具，对比研究了蓝失谐和红失谐的光学偶极力对坍缩临界参数及坍缩延迟的影响，并讨论了不对称的光学偶极力给BEC坍缩带来的可能的效应。 |
| 英文摘要 | This thesis studies the Bose-Einstein condensation both experimentally and theoretically. The investigations include two parts. The first part involves the discussions for the preparation of BEC, and the proposal for a new type of periodical magnetic microtrap for cold atoms. Then we discuss some points of the first BEC experiment of China, focusing on the building and measuring of our QUIC trap, the design of the timing control program, and the experiment process and results. The second part involves some theoretical work. We first introduce the general framework of the mean-field theory of BEC. During these discussions, we thoroughly study several analytical approaches and the numerical simulation method. Then we apply these methods'to the problem of the stability of BEC in the GP formulation. Next we discuss the interaction between cold atoms, such as Fermi pseudopotential, and Feshbach resonance, after which we introduce a new type of quantum defect theory which is angular-momentum-insensitive. Based on this theory, we propose a new modified GP equation. Comparison of the ground state energy with Monte Carlo results shows that this equation substantially improves the predication of the ground state energy relative to GP formulation. The last chapter concentrates on the dynamical collapse of BEC with an (tunable) attractive interaction. We first study the time delay of the collapse. We identify the delay comes from the amassing process of the particle density in the center of the condensation. Numerical simulation results exhibits the same trend of the experimental curve and a relatively good comparison with the experiment is found. Then we notice that the initial shape oscillation of the condensate before collapse begins effects the collapsing dynamics, which is ignored in the experiment. We show that the time delay synchronizes the initial collective oscillation of the condensate by numerical simulation. Next we propose using the optical plug to control the collapse of BEC, which is an analog to the optical plug for the Majorana transition of the cold atoms in the magnetic quadrupole field. We intensively study the effect of the optical plug on the collapse, and we found that when the strength of the plug is strong enough, a new type of collapse occurs, which is topologically different from that so-called central collapse currently studied in the literature. Detailed investigations are contributed to the effect of the optical plug on the critical interaction strength and its consequence in this section. In the last section, we generalize the concept of the optical plug for the collapse and propose using the optical dipole force as an optical microsurgery to the collapse. Effects of the both blue-detuned and red-detuned optical microsurgery on the critical interaction strength and the time delay are studied numerically, and possible effects of an asymmetry optical dipole force are discussed. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15534]  |
| 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 | 付海翔. 气态玻色-爱因斯坦凝聚实验及若干理论问题研究[D]. 中国科学院上海光学精密机械研究所. 2003. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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