复杂超冷原子气体系统中的少体问题研究

The research on ultracold atomic gas systems is a frontier of modern physics. Through decades course of the development, cold atom physics absorbed many advanced technology and research methods from other branches of physics, and embrace continuously new research hotspots as disciplinary interacting. Atoms and molecules have rich internal structures, whose properties can be controlled precisely through light and magnetic fields, rendering them ideal platform for quantum manipulation and control, possessing broad application prospects. Research of these years has extended to situations with more complicated external and internal conditions, and discovered new physical behaviors, also raised new physical problems and challenges. Based on previous experiences, research on few-body problems can provide essential help for understanding many-body properties. The aim of this project is actually based on the current research, and dig deeper on few-body problems of more complicated ultracold atomic gas systems, to calculate bound state spectrum and scattering characteristics of few-body systems, and to reveal novel few-body physical paradigms, and to understand physical properties of many-body physics through methods including virial expansions.

对于超冷原子气体系统的研究是当代物理学的前沿领域。在几十年的发展过程中冷原子物理学吸收了多个物理学分支的前沿技术和研究方法，并随着学科交叉不断产生新的研究热点。原子分子具有丰富的内部结构，其性质可以通过光场磁场等进行精确控制，是实现量子调控的绝佳平台，具有广阔的应用前景。近年来的研究扩展到了有各种外在和内在条件更复杂的情形，并发现了新的物理现象，也提出了新的物理问题和挑战。根据以往的经验，研究少体问题能为理解多体系统的性质提供关键性帮助。本项目的主要目的就是在已有的研究基础上，对更复杂的超冷原子气体系统中的少体问题进行深入研究，计算少体系统的束缚态能谱和散射特性，揭示新的少体物理范式，并通过维里展开等方法理解多体系统的物理性质。

本项目围绕复杂超冷原子气体中的少体问题主要进行了三方面的研究，包括量子三体的散射特性和理论方法、基于Efimov效应的动力学新范式、幺正极限下的普适动力学。.（1）我们系统性研究了异核混合三体系统的散射特性，揭示了弱两体相互作用可显著调控原子-分子散射乃至引发共振；我们还发展了一种普适理论方法以正确计入不同能量尺度的两体束缚态对三体散射的贡献。相关研究成果发表于Physical Review A和Communications in Theoretical Physics。.（2）我们研究了量子系统的淬火动力学，预言了如果淬火后的哈密顿量具有离散标度对称性那么其后续演化可以呈现分形行为。这种行为是Efimov效应在动力学上的体现。这一发现发表于Physical Review Letters。.（3）我们研究了淬火两体相互作用的问题，证明了两体系统在淬火至幺正极限后的长时极限下会达到稳态并给出了初态与终态的严格关系；藉此我们研究了对应的多体问题版本，最终定性地解释了最近实验【Nature 563, 221（2018）】发现的新型普适行为。此成果已被Physical Review Letters接收并即将发表。