冷原子高效磁阱转移和用于拉曼耦合的光学锁相环系统的研究

发布时间：2018-05-06 16:01

本文选题：玻色-爱因斯坦凝聚 + 磁转移　；参考：《山西大学》2016年博士论文

【摘要】：本文首先介绍了如何从相对低真空度的真空腔室中俘获高密度超冷玻色气体,然后运用磁转移的办法,将原子高效率的装载到超高真空度的二级磁阱中,然后使用远失谐的532nm激光封堵磁场零点,之后进行蒸发冷却,最后将87Rb的超冷原子装载到远失谐的交叉偶极阱中,进而实现玻色-爱因斯坦凝聚。在俘获原子、磁转移冷原子的实验部分,首先回顾了一些常用的冷却技术和概念,其中包括激光冷却、磁光阱等。然后描述了超冷原子的超高真空腔室系统、实现超高真空度的方法、搭建简单可靠稳定的激光光路、设计四级阱线圈和磁转移线圈、编写磁转移程序和设计控制电路从而使得四级阱和磁转移线圈有序的相互配合、编写CCD程序从而配合飞行展开吸收成像。在实验的关键部分,做了详细的介绍,例如磁转移线圈的配合部分。其次本文还介绍了锁相环的基本原理,分析了不同种类的鉴相器的优缺点和实用性。为了获得低噪声、相位相干、差频大的两束拉曼激光,介绍了如何将电子锁相环推广到光学锁相环,并且设计了光学锁相环,分析了在调节电路过程中的一些关键部件。使用光学锁相环调制外腔反馈式半导体激光器的压电陶瓷和电流,进而使得非相关联的两束激光线宽从MHz降低到Hz量级,它们的相噪大幅度降低,将锁定的两束拉曼激光照射到超冷原子上,测量了原子态的拉比振荡。本文最后介绍了使用两束拉曼激光作用在超冷原子中模拟电子自旋轨道耦合的模型,并且成功模拟了自旋轨道耦合,然后将一维的自旋轨道耦合推广到二维空间,使用三束线偏振拉曼光实现了二维自旋轨道耦合,通过调节拉曼光的失谐大小,实现了狄拉克在动量空间的位置变化。为了拓展二维自旋轨道耦合的应用(模拟拓扑霍尔效应等),在其中一束拉曼光的光路中加入/4波片,由此使得线偏光椭圆极化,由此在二维自旋轨道耦合的哈密顿量中构建了垂直于拉曼激光平面的塞曼磁场哈密顿量,通过调节入/4波片的角度(调节椭圆极化率),就可以调节塞曼磁场的大小,由此就将狄拉克点处的带隙打开,并且通过改变波片的角度可以精确调节带隙的大小。自旋轨道耦合的原子态之间存在相互作用力,我们通过自旋射频光谱的技术,使用射频将原子泵浦到无相互作用的量子态上,通过能量守恒倒推出相互作用的量子态的能量色散关系图。
[Abstract]:In this paper, we first introduce how to capture the high-density ultra-cold Bose gas from the vacuum chamber with relatively low vacuum, and then use the method of magnetic transfer to load the atom efficiently into the second-order magnetic trap with ultra-high vacuum. Then a remote detuned 532nm laser is used to block the magnetic field zeros, and then evaporative cooling is performed. Finally, the supercooled atoms of 87Rb are loaded into the far detuned cross dipole trap, and the Bose-Einstein condensation is realized. In the experimental part of capture atoms and magnetically transferred cold atoms, some commonly used cooling techniques and concepts are reviewed, including laser cooling, magneto-optic trap and so on. Then, the ultra-high vacuum chamber system of ultra-cold atoms is described, the method of realizing ultra-high vacuum degree, the simple and reliable laser light path, the design of four-well coil and magnetic transfer coil are designed. The magnetic transfer program and control circuit are designed to make the four-well and magnetic transfer coil cooperate in an orderly way, and the CCD program is written to develop absorption imaging with flight. The key parts of the experiment are introduced in detail, such as the matching part of the magnetic transfer coil. Secondly, the basic principle of PLL is introduced, and the advantages and disadvantages and practicability of different kinds of PLL are analyzed. In order to obtain two Raman lasers with low noise, coherent phase and large frequency difference, this paper introduces how to extend electronic phase-locked loop to optical phase-locked loop, designs optical phase-locked loop, and analyzes some key components in the process of adjusting circuit. Using optical phase-locked loop (OPLL) to modulate the piezoelectric ceramics and current of the external cavity feedback semiconductor laser, the linewidth of the non-correlated two beams is reduced from MHz to Hz, and their phase noise is greatly reduced. Two locked Raman lasers were irradiated onto the supercooled atoms, and the rabbi oscillations of the atomic states were measured. In the end, the model of electron spin orbit coupling in ultracold atoms using two Raman laser beams is introduced. The spin orbit coupling is successfully simulated, and then the one-dimensional spin orbit coupling is extended to two dimensional space. Two-dimensional spin orbit coupling is realized by using three-beam linearly polarized Raman light and Dirac's position in momentum space is realized by adjusting the detuning size of Raman light. In order to extend the application of 2-D spin orbit coupling (simulating topological Hall effect etc.), we add 4 wave plates to one of the Raman beams, which leads to the elliptical polarization of linear polarized light. Thus, a Zeeman magnetic field Hamiltonian perpendicular to the Raman laser plane is constructed in the 2-D spin orbit coupling Hamiltonian. By adjusting the angle of the four-wave plate (adjusting the elliptical polarizability), the size of the Zeeman magnetic field can be adjusted. Thus the band gap at the Dirac point is opened and the size of the band gap can be accurately adjusted by changing the angle of the wave plate. There is an interaction between the spin orbit coupled atomic states, and we pump the atoms to quantum states without interaction by using the technique of spin radio frequency spectroscopy. The energy dispersion diagram of the interacting quantum states is derived from the conservation of energy.
【学位授予单位】：山西大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O469

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