【作者】 胡丽娜；

【导师】 孙建安； 豆福全；

【作者基本信息】 西北师范大学 ， 理论物理， 2020， 硕士

【摘要】 超冷原子分子的研究是超冷量子气体领域的一个前沿课题,具有非常重要的理论价值和广阔的应用前景.该研究广泛应用于强相互作用超流、相干分子光学、精密测量、凝聚态物理等领域且发挥着其独特的作用.光缔合和磁共振是超冷原子-分子转化的常用技术,转化过程中通常采用Landau-Zener模型进行描述.但此模型有一定的局限性.为克服这些局限性,越来越多的模型被应用于超冷原子-分子转化中.本文主要研究周期外场下超冷原子-分子转化动力学,分别运用高斯脉冲串模型与周期调制场研究超冷原子-分子转化,分析其相应的动力学行为和产生的一些有趣现象.本文的主要研究内容以及结构安排如下:第一章简要介绍超冷原子-分子转化的意义、常用方法以及相关的背景知识.概述了超冷双原子分子转化的基本模型,综述了高斯脉冲串模型和周期调制场在超冷原子系统中应用的研究现状.第二章主要研究啁啾高斯脉冲串模型下超冷原子-分子转化动力学.基于平均场理论,研究了不同外场参数如耦合强度、扫描速率以及脉冲串个数对超冷原子-分子转化的影响.通过调节这些参数,发现系统中存在新颖的干涉现象.通过稳相近似方法获得了原子-分子转化效率的解析表达式.研究结果表明将高斯脉冲串模型应用于超冷原子-分子转化,可实现干涉相长、干涉相消等动力学行为,从而通过调节外场进一步提高原子到分子的转化效率.第三章研究了超冷原子-分子转化动力学的周期调制效应.基于平均场理论,采用周期调制场分析超冷原子-分子转化动力学.通过调节外场参数,系统中发现了一些有趣的干涉现象和共振现象.当系统中存在粒子间相互作用时超冷原子-分子转化系统中的干涉图样呈现出不对称性,干涉条纹的位置也发生了显著偏移.同时也分析了耦合强度对共振峰的影响.最后,通过数值计算验证了理论结果.第四章对本文的工作进行了总结,并对该领域的研究前景和下一步工作进行了展望.更多还原

【Abstract】 The study of ultracold atom molecule is a frontier subject in the field of ultracold quantum gases,which has important theoretical values and broad application prospects.The research has widely used strongly interacting superfluid,coherent molecular optics,precision measurement,and condensed-matter physics,etc.Photoassociation and magnetic resonance are widely used production techniques of ultracold atoms to molecules.This conversion process is usually described by the Landau-Zener model,but this model has some limitations in certain situations.In order to overcome these limitations,more and more models have been applied to the ultracold atom-molecule conversion.In this thesis,we mainly study ultracold atom-molecule conversion dynamics in periodic external field.Using Gaussian pulse train model and periodic modulation field to study the ultracold atom-molecule conversion and analyze corresponding dynamic behavior,as well as some interesting phenomena.The main contents and structure of this thesis are as follows:In the first chapter,the significance,common methods and relevant background knowledge of ultracold atom-molecule conversion are introduced.The basic models of ultracold diatomic molecules conversion are summarized.The application of Gaussian pulse train model and periodic modulation field in the ultracold atomic system is summarized.In the second chapter,we study the conversion dynamics of ultracold atoms to molecules in the chirped Gaussian pulse train model.Under the mean-field theory,the effects of different external field parameters such as coupling strength,sweep rate and the number of pulse trains on the conversion of ultracold atoms to molecules are studied.By adjusting these parameters,it is found that there are novel patterns of interferences in the system.In addition,the analytical expression of ultracold atom-molecule conversion efficiency is obtained by the stationary phase approximation.The result shows that the dynamic behaviors of constructive and destructive interferences can be realized by applying the Gaussian pulse train model to the ultracold atom-molecule conversion,and atommolecule conversion efficiency can be further improved by adjusting the external field.In the third chapter,we study the periodic modulation effect of ultracold atom-molecule conversion dynamics.By adjusting the external field parameters,some interesting interference and resonance phenomena are produced in the system.It is found that the interference patterns are asymmetric and the positions of the interference fringes are shifted significantly in the ultracold atom-molecule conversion system,when there is particle interaction.At the same time,we analyze the influence of coupling strength on the resonance peaks.Finally,the theoritical result is verified by numerical calculation.In the fourth chapter,the work of this thesis is summarized,and the research prospect and the further work in this field are prospected.更多还原