External Field Control of Ultracold Atom-Molecule Mixtures: Quantum Collision Dynamics, Chemical Reactions, and Sympathetic Cooling

该项目旨在开发一种新的，严格的，计算效率高的量子散射方法，用于在外部电磁场存在下的低温原子分子碰撞和化学反应的理论描述。需要一种新的方法来扩大可以冷却到量子现象占主导地位的超冷温度的分子种类的数量和种类。直到最近，可用于超冷领域实验的分子种类的范围一直限于那些可以通过激光诱导超冷碱金属原子结合产生的双原子分子。要将这个范围扩大到包括更复杂的分子种类，需要采用适当的冷却技术，特别是所谓的交感冷却，通过这种技术，在超冷碱金属原子“浴”内的弹性原子-分子碰撞有助于降低参与分子的温度。交感冷却的过程是有效的，前提是可以抑制可能在内部加热分子或可能将它们从捕获环境中驱逐的非弹性碰撞。精确描述相关碰撞过程的计算要求是严格的，因为所涉及的分子是高度各向异性的，并且因为分子的捕获场环境通常也是各向异性的。 本研究将为实验组的共振冷却技术的研究提供理论支持。如果这项技术成功，它将大大扩展超冷状态下可用的分子种类范围，对基于超冷分子的量子信息处理、量子模拟、受控化学和基本对称性测试产生深远影响。作为改进方法的基础，分子散射态的总角动量表示将被使用。该方法将被应用于阐明交感神经冷却的实验相关的极性分子CaH，SrF，和SrOH与碱金属原子Li和Rb的磁和磁光陷阱的前景。科学家们还将探索通过调整分子塞曼状态，诱导振动Feshbach共振以及施加叠加电场和磁场来控制原子分子化学反应的新方案。该项目支持的研究生将获得量子散射理论，分子物理，数值分析和计算机编程方面的广泛培训，这将使他们能够与领先的实验小组合作，并获得国际认可。拟议的工作将原子和分子物理学与物理化学领域联系起来，从而加强了里诺纳瓦达大学物理和化学系之间的研究合作。

This project aims at the development of a new, rigorous, and computationally efficient quantum scattering methodology for the theoretical description of low-temperature atom-molecule collisions and chemical reactions in the presence of external electromagnetic fields. A new methodology is needed in order to expand the number and variety of molecular species that can be cooled to the ultra-cold temperatures at which quantum phenomena become dominant. Until recently, the range of molecular species available for experiments in the ultra-cold domain has been limited to those diatomic molecules which can be produced by laser-induced binding of ultra-cold alkali-metal atoms. Expanding this range to include more complex molecular species requires the adoption of appropriate cooling techniques, especially so-called sympathetic cooling, by which elastic atom-molecule collisions within an ultra-cold alkali-metal atom "bath" serve to reduce the temperature of the participating molecules. The process of sympathetic cooling is effective providing that inelastic collisions which could internally heat the molecules, or which might expel them from the trapping environment, can be suppressed. The computational requirements for the accurate description of the relevant collisional processes are stringent, because the molecules involved are highly anisotropic, and because the trapping field environment of the molecule is also generally anisotropic. This project will provide much needed theoretical support to experimental groups honing the sympathetic cooling technique. If the technique is successful, it will drastically extend the range of molecular species available in the ultra-cold regime, with far-reaching implications for ultra-cold molecule-based quantum information processing, quantum simulation, controlled chemistry, and fundamental symmetry tests. As a basis for the improved methodology, the total angular momentum representation of molecular scattering states will be used. The methodology will be applied to elucidate the prospects for sympathetic cooling of the experimentally relevant polar molecules CaH, SrF, and SrOH with the alkali-metal atoms Li and Rb in magnetic and magneto-optical traps. The scientists will also explore new scenarios for controlling atom-molecule chemical reactions via tuning molecular Zeeman states, inducing vibrational Feshbach resonances, and applying superimposed electric and magnetic fields. The graduate students supported by this project will get extensive training in quantum scattering theory, molecular physics, numerical analysis, and computer programming, which will allow them to engage in collaboration with leading experimental groups, and gain international recognition for their research. The proposed work connects the fields of atomic and molecular physics and physical chemistry, thereby enhancing research collaborations between the Physics and Chemistry Departments of the University of Navada, Reno.