强相互作用和二维自旋—轨道耦合的超冷费米气体

发布时间：2018-05-13 13:50

本文选题：二维自旋—轨道耦合 + Rashba型和Dresselhaus型自旋—轨道耦合　；参考：《山西大学》2016年博士论文

【摘要】：近年来,自旋—轨道耦合的超冷原子气体引起了人们极大的兴趣。利用自旋轨道耦合的超冷原子系统可以模拟研究许多与带电粒子在电磁场中的物理行为相关的许多有趣的物理现象,如量子霍尔系统、自旋霍尔效应、拓朴绝缘体、p-wave超导体以及Majorana费米子等。本论文主要介绍基于我们87Rb玻色子和40K费米子的超冷原子系统上最近所做的一些工作：在超冷费米气体中研究了射频场对Feshbach共振的散射控制；自旋—轨道耦合对Feshbach分子的解离效应做了实验和理论研究；在简并费米气体中首先实现了二维的人造自旋—轨道耦合；在二维自旋—轨道耦合的费米气体中观测打开拓朴能隙并做了相应的研究。对Rashba型和Dresselhaus型自旋—轨道耦合以及由该两种类型等权叠加的拉曼光诱导产生的—维自旋—轨道耦合做了简单介绍；并对自旋—轨道耦合中的拉曼耦合强度做一个详细的理论描述；为了在实验中选择一个合适的参数,实验研究了拉曼光波长和外部磁场对自旋—轨道耦合的耦强度的影响。实验研究了超冷费米气体中磁场Feshbach共振的射频场调节控制。通过磁场Feshbach共振技术,扫描磁场产生弱束缚的Feshbach分子,改变的射频场频率,观测基态Feshbach分子到基态深束缚分子的能级跃迁,观测到了三个束缚态到束缚态的共振跃迁。固定射频场在某个能级跃迁的附近,测量了原子数随磁场的变化,在宽的Feshbach共振背景曲线上出现非常窄的损耗,非常窄的损耗是由射频场产生,重新得到一个存在射频场时Feshabch共振的损耗轮廓。实验表明可以采用外部射频场,可以调节Feshbach共振的散射特性,也就是调节原子之间的相互作用,该技术为操控BEC到BCS的过渡区域提供了可能；在超冷费米气体中,当存在自旋—轨道耦合时,我们在实验上在不同的磁场、不同的耦合强度等条件下观测了该效应对Feshbach分子的解离效应,并分别对动量对Feshabch分子解离的重要性、依赖于失谐的分子解离效应以及在解离过程中剩余的分子数进行了理论分析和数值计算。在超冷费米气体中我们小组首次实现二维的人造自旋—轨道耦合,在理论上对二维自旋—轨道耦合进行分析和预测,在实验中通过自旋注入的方式测量得到二维自旋—轨道耦合的能谱并且得到一个高度稳定可控的狄拉克点,并且得到狄拉克在动量空间的运动轨迹。基于已经实现的二维自旋—轨道耦合的超冷费米气体,我们理论分析并设计了如何打开狄拉克点处能隙的简单易行的实验方案,并通过调节拉曼激光的偏振来实现该方案。实验中测量得到该方案下缀饰态原子的能量—动量色散谱并对狄拉克点处的拓朴能隙进行了精确测量。
[Abstract]:In recent years, supercooled atomic gases coupled with spin-orbit have attracted great interest. Many interesting physical phenomena related to the physical behavior of charged particles in electromagnetic fields, such as the quantum Hall system, the spin Hall effect, can be simulated by using a spin-orbit coupled supercooled atomic system. Topological insulators, p-wave superconductors and Majorana fermions. In this paper, we mainly introduce some recent works based on our 87Rb boson and 40K fermion supercooled atomic system: the scattering control of Feshbach resonance by RF field in ultra-cooled Fermi gas is studied; The spin orbital coupling has been used to study the dissociation effect of Feshbach molecule experimentally and theoretically, and the two dimensional artificial spin orbital coupling has been realized in degenerate Fermi gas. The topological energy gap is observed and studied in the two dimensional spin-orbit coupled Fermi gas. The spin-orbit coupling of Rashba type and Dresselhaus type and the spin-orbit coupling induced by Raman light induced by the two types of equal weight superposition are briefly introduced. In order to select a suitable parameter in the experiment, the effects of Raman wavelength and external magnetic field on the coupling strength of spin-orbit coupling are studied. The RF field control of magnetic field Feshbach resonance in supercooled Fermi gas is experimentally studied. By means of magnetic field Feshbach resonance technique, the weak bound Feshbach molecule is generated by scanning the magnetic field, the frequency of RF field is changed, the energy level transition from ground state Feshbach molecule to ground state deep bound molecule is observed, and the resonance transition from bound state to bound state is observed. The change of atomic number with magnetic field has been measured in the vicinity of a certain energy level transition in a fixed radio frequency field. The very narrow loss appears on the wide Feshbach resonance background curve, and the very narrow loss is generated by the radio frequency field. A loss profile of Feshabch resonance in the presence of RF field is obtained again. The experimental results show that the external RF field can be used to adjust the scattering characteristics of Feshbach resonance, that is, the interaction between atoms. This technique makes it possible to control the transition region between BEC and BCS. In the presence of spin-orbit coupling, we have experimentally observed the dissociation effect of this effect on Feshbach molecules under different magnetic fields and different coupling intensities, and the importance of momentum to the dissociation of Feshabch molecules, respectively. The molecular dissociation effect dependent on detuning and the number of molecules remaining in the dissociation process are theoretically analyzed and numerically calculated. In the supercooled Fermi gas, our team first realized the two dimensional spin orbit coupling, and theoretically analyzed and predicted the two dimensional spin orbit coupling. In the experiment, the energy spectrum of two dimensional spin-orbit coupling is measured by spin injection, and a highly stable and controllable Dirac point is obtained, and the motion trajectory of Dirac in momentum space is obtained. Based on the realized two-dimensional spin-orbit coupled super-cooled Fermi gas, we theoretically analyze and design a simple experimental scheme of how to open the energy gap at Dirac point, and realize this scheme by adjusting the polarization of Raman laser. The energy-momentum dispersion spectra of the decorated atoms under the scheme are measured and the topological energy gap at the Dirac point is accurately measured.
【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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