CAREER: Control and Analysis of Atomic Few-Body Dynamics

理解相互作用的粒子系统是物理学的关键挑战之一，具有基础和技术上的相关性。这样的系统通常不能以封闭的分析形式(可以写下来的数学表达式)完整地描述两个以上的粒子，即使它们的单独性质和它们之间的力是精确已知的。这一困境被称为“少体问题”，它限制了人们在未来任何时间预测粒子状态(例如，它们的位置和速度)的程度。因此，推进对由于几个粒子的复杂相互作用而出现的现象的认识，需要针对广泛的情况进行联合的理论和实验探索。在这个项目中，将研究由原子及其带电成分(电子和离子)和光子(光的粒子)组成的量子系统的少体现象。这样的量子系统是少体物理的理想试验场，原因有很多：首先，这些系统中的少体效应无处不在，与许多研究领域和众多技术应用有关，特别是在材料科学、量子化学、生物科学和信息处理等领域。其次，先进的实验技术允许以高度的可控性和精确度操纵少粒子量子态的参数。此外，现代光谱仪能够拍摄状态随时间变化的快照，从而能够分析状态动态的细节。过去二十年发展起来的控制原子少体系统和分析其动力学的技术(基本上是相互独立的)将首次结合在本项目中。这将使观察少体量子现象的同时能够调整系统参数，并将允许基准理论模型。在更技术的层面上，这个项目涉及使用激光冷却和操纵技术来控制和分析原子少体系统，以准备各种初始态，从单个激发或极化的锂原子到冷却到量子简并的大型原子系综。只有极少数原子的系统可以被限制在微米大小的光学偶极陷阱中，并且它们的相互作用可以被调节到接近费什巴赫共振。为了进行分析，将使用“反应显微镜”，允许对飞秒或阿秒激光脉冲电离锂原子后原子碎片的动量矢量进行符合测量。本质上，在提议的实验中有三个基本问题需要解决：第一，电离动力学如何取决于电离激光场和极化目标原子的相对取向(或螺旋度)？这类实验将有助于理解基本对称性，并最终控制激光场与手性(原子或分子)靶的相互作用，手性靶在生物化学中发挥着至关重要的作用。第二，原子由于与电离场的相互作用而产生的解体是如何受其环境影响的？这在实验上只对星团或固体目标进行了研究，但在更稀薄的系统中基本上没有被探索。除了这个问题的基本重要性外，电离动力学对环境的依赖也与理解辐射对生物组织的损害有关。最后，作为粒子数、相互作用类型和强度的函数，少数粒子系统的关联波函数是如何变化的？“设计”简单的少体系统并全面观察这类系统的可能性，将使人们能够“模拟”和理解发生在天然或人造材料中的基本量子现象。

Understanding systems of interacting particles is one of the key challenges of physics, and has both fundamental and technological relevance. Such systems generally cannot be fully described in closed analytical form (mathematical expressions that can be written down) for more than two particles, even if their individual properties and the forces between them are precisely known. This dilemma is well-known as the "few-body problem" and it limits the extent to which one can predict the states of the particles (e.g. their positions and velocities) for any time in the future. Therefore, advancing the knowledge of phenomena that emerge due to the complex interplay of several particles requires the joined theoretical and experimental exploration for a wide range of situations. In this project, few-body phenomena of quantum systems consisting of atoms, their electrically charged components (electrons and ions), and photons (the particles of light) will be studied. Such quantum systems represent an ideal testing ground of few-body physics for multiple reasons: First, few-body effects in these systems are ubiquitous and relevant to many research fields and numerous technical applications, particularly in areas such as materials science, quantum chemistry, biological science, and information processing. Second, advanced experimental techniques are available which allow manipulation of the parameters of the few-particle quantum state with a high degree of control and accuracy. Moreover, modern spectrometers enable snapshots to be taken of the state's change over time, allowing details of the state's dynamics to be analyzed. Techniques for the control of atomic few-body systems and for the analysis of their dynamics which have been developed in the past twenty years (largely independently of each other) will be combined in the present project for the first time. This will enable the observation of few-body quantum phenomena while being able to tune the system parameters, and it will allow benchmarking theoretical models.On a more technical level, this project involves the control and analysis of atomic few-body systems using laser cooling and manipulation techniques to prepare a large variety of initial states, ranging from single excited or polarized lithium atoms to large ensembles of atoms that are cooled to quantum-degeneracy. Systems of only very few atoms can be confined in a micrometer-sized optical dipole trap and their interaction can be tuned close to Feshbach resonances. For the analysis, a "reaction microscope" will be employed allowing the coincident measurements of the momentum vectors of atomic fragments after ionization of the lithium atoms by femtosecond or attosecond laser pulses. In essence, there are three fundamental questions to be addressed in the proposed experiments: First, how do the ionization dynamics depend on the relative orientation (or helicity) of an ionizing laser field and a polarized target atom? Such experiments will help to understand fundamental symmetries and ultimately control the interaction of laser fields with chiral (atomic or molecular) targets, which play a crucial role e.g. in biochemistry. Second, how is the disintegration of an atom due to the interaction with an ionizing field influenced by its environment? This is experimentally only studied for clusters or solid targets, but largely unexplored for more dilute systems. Apart from the fundamental importance of this question, the dependence of the ionization dynamics on the environment is relevant to the understanding of the damage of biological tissue due to radiation. Finally, how does the correlated wave function of a few-particle system change as a function of the particle number and interaction type and strength? The possibility to "engineer" simple few-body systems and observe such systems comprehensively would allow one to "simulate" and understand fundamental quantum phenomena that occur in natural or artificial materials.