Physics with New Molecular Systems: Quantum Interactions, Cooling, and Applications

原子是自然界的基本组成部分，它们的行为受一种叫做量子力学的微观物质理论的支配。我们对自然界中几乎所有事物的理解都依赖于应用于原子及其近亲分子（两个或更多的原子通过化学键连接在一起）的量子力学。从人类和其他生物到计算机和互联网，物理系统只能通过了解原子和分子的详细行为来解释。然而，尽管量子力学在描述非常简单的原子系统方面非常成功，但我们还不知道如何定量地应用这一理论来描述我们所看到的所有现象。特别是，为了发明新的技术和生物物质，我们需要更好地理解原子和分子的量子力学。许多物理学（包括原子物理学）的最终目标是对所有物质有一个完整的理解，并拥有发明新类型物质的工具。这个项目是对极低温下气体中原子和分子之间相互作用的详细量子理解的一步。当冷却时，原子和分子的量子性质被大大放大，暴露其本质，仔细研究。这项工作的基本实验方法是利用原子和分子的磁捕获来使用激光光谱研究它们的碰撞。技术方法将是使用缓冲气体冷却来形成原子和分子束，当它们通过捕获区域时，将被光泵入磁捕获状态。光束中一半的分子最初处于低场寻找量子态。当这些分子接近陷阱的最大磁场时，它们会失去能量，在那里它们将被光泵送到高场寻找状态。然后这些分子在向陷阱中心移动的过程中继续失去能量。在陷阱中心附近，激光将分子泵入它们的陷阱状态。在这个过程中只有两个光子被散射，这（以及分子通过陷阱时的能量损失）导致了不可逆的陷阱加载。我们将用这种方法将一氟化钙分子和其他小分子捕获到磁阱中。原子也可以与分子共载，在足够高的密度下进行蒸发冷却。我们将共同加载锂和/或钾原子，研究它们与被困分子之间的碰撞，测试分子理论，并研究利用交感冷却实现超冷分子的途径。光谱学将揭示分子的状态分布，以及它们的数量和温度。对陷阱损失的研究可以用于研究自旋弛豫碰撞（对于某些原子-分子对有详细的理论）。这项工作的长期目标是从双原子和三原子分子开始，观察越来越复杂的原子分子碰撞中的能量交换和其他现象。这将增加我们对自然的基本理解，并帮助科学设计新的物理系统和化学和生物学的新工具。

Atoms are the basic building blocks of nature and their behavior is governed by a microscopic theory of matter called quantum mechanics. Our understanding of nearly everything we see in nature relies on quantum mechanics as applied to atoms and their close cousins, molecules (two or more atoms stuck together by a chemical bond). From humans and other living things to computers and the internet, physical systems can be explained only by knowing how atoms and molecules behave in detail. Yet, although quantum mechanics has been very successful in describing very simple atomic systems, we do not yet know how to apply the theory quantitatively to describe all the phenomena that we see. In particular, to invent new technological and biological substances, we need to understand the quantum mechanics of atoms and molecules better. The eventual goal of much of physics (including atomic physics) is to have a complete understanding of all matter and the tools to invent new types of matter. This project is a step toward developing a detailed quantum understanding of the interactions between atoms and molecules in a gas at a very low temperature. When cooled, the quantum nature of atoms and molecules is greatly amplified, exposing its nature to careful study. The essential experimental approach to this work is to use magnetic trapping of atoms and molecules to study their collisions using laser spectroscopy. The technical method will be to use buffer-gas cooling to form a beam of atoms and molecules, which will be optically pumped into magnetically trapped states as they pass through the trapping region. Half the molecules in the beam are originally in the low-field-seeking quantum state. These molecules lose energy as they approach the magnetic field maximum of the trap, where they will be optically pumped into their high-field-seeking state. These molecules then continue to lose energy as they travel toward the trap center. Near the trap center lasers pump the molecules into their trapped state. Only two photons are scattered in this process and this (along with energy loss as the molecules pass through the trap) leads to irreversible trap loading. We will trap molecules of calcium monofluoride and other small molecules into a magnetic trap using this method. Atoms can also be co-loaded with molecules, at high enough density for evaporative cooling. We will co-load lithium and/or potassium atoms and study collisions between them and the trapped molecules, testing molecular theory and investigating a route toward ultracold molecules using sympathetic cooling. Spectroscopy will reveal both the state distribution of the molecules, as well as their number and temperature. Investigation of trap loss can be used to study spin-relaxation collisions (for which there is detailed theory for some atom-molecule pairs). The longer term goal of this work is to enable observation of exchange of energy and other phenomena in increasingly complex atom-molecule collisions, starting with diatomic and triatomic molecules. This will add to our fundamental understanding of nature and help science to design new physical systems and new tools for chemistry and biology.