Coherent Control of Cold Collision by Preparing Molecular Eigenstates Using Stark-Induced Adiabatic Passage

摘要：该项目侧重于在最基本的水平上发展对驱动分子相互作用（包括化学反应）的量子力学过程的全面理解。本研究的主要目标是探索量子系统的特性并提高我们操纵它们的能力，这在包括实现量子计算机在内的各种应用中具有重要意义。研究小组将在定义良好的量子态下制备分子，进行低能（冷）碰撞实验。通过将入射粒子的量子态与出射粒子的量子态相关联，他们将探索制造和破坏化学键所涉及的量子力学相互作用。这项研究结合了尖端的量子光学技术和激光光谱学的专业知识，以及使用超音速扩展分子束的状态分辨碰撞动力学。参与该项目的研究生将学习使用真空紫外激光脉冲进行多光子激光光谱学所需的技术技能，使用复杂的单模脉冲激光系统制备量子态，以及操作超音速光束。此外，研究小组将设计一个高分辨率质谱仪来解决冷碰撞中的散射角分布。这种在量子物理和化学的广泛领域的全面培训将帮助学生准备成为改善未来科学技术的领导者。摘要：要理解化学反应中涉及的量子力学过程，必须找到实验测量和理论计算之间的直接对应关系。为了实现这一目标，实验人员需要选择理论上易于处理的分子，如H2 （N2， CO等），这些分子也与当前科学相关。研究人员将使用一种称为多步斯塔克诱导绝热拉曼通道（multi-step SARP）的相干光学技术制备高振动状态的双原子分子。多步SARP是本课程组早期开发的SARP过程的推广，它可以将大量H2分子泵送到各种振动激发水平。多步SARP将两个或多个SARP过程结合起来，以实现接近完全的种群转移到非常高的振动激发水平。研究人员已经从理论上证明，通过将几个斯托克斯脉冲组合在一个更强的泵脉冲的机翼上，有可能达到非常高的振动状态。该技术的长期前景包括制备H2的最高振动能级，甚至达到振动解离连续体，产生一对纠缠松散结合的氢原子。这些奇异的量子系统将使研究人员能够克服冷碰撞和超冷碰撞中的反应屏障，并测试基本的量子物理原理，例如碰撞中的干涉。该项目的第一个目标是建立多步骤SARP实验，并演示制备非常高振动激发水平的H2。选择多步SARP中使用的激光偏振将允许控制高振动激发分子的键轴对齐。使用两步SARP过程激发非常高的振动态将是冷分子碰撞研究中的一个重大飞跃。制备完成后，研究人员将在H2和D2的超音速扩展混合光束中对四中心反应H2 + D2→2HD进行冷散射实验。高振动激发H2分子的碰撞动力学对于理解和模拟星际介质的物理和化学具有巨大的兴趣。此外，H2的高振动水平被认为是通过低能电子的解离附着有效产生H束的必要条件，这在点燃聚变反应堆中具有重要的应用。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

General audience abstract:This project focuses on developing a comprehensive understanding of the quantum mechanical processes that drive molecular interactions including chemical reactions at the most fundamental level. The main goal of this research is to explore the character of quantum systems and improve our ability to manipulate them, which is of great importance in various applications including realization of a quantum computer. The research team will carry out low energy (cold) collision experiments with molecules prepared in well-defined quantum states. By correlating the quantum states of the incoming particles with those of the outgoing particles they will explore the quantum mechanical interactions involved in making and breaking chemical bonds. This research combines cutting edge quantum optical techniques and expertise in laser spectroscopy with state-resolved collision dynamics using a supersonically expanded molecular beam. The graduate students involved in this project will learn the technical skills needed for multiphoton laser spectroscopy using vacuum ultraviolet laser pulses, quantum state preparation using sophisticated single-mode pulsed laser systems, and manipulation of a supersonic beam. Additionally, the research team will design a high resolution mass spectrometer to resolve the scattering angular distribution in cold collisions. This comprehensive training in broad areas of quantum physics and chemistry will help to prepare the students to be leaders in improving the science and technology of tomorrow. Technical audience abstract:To understand the quantum mechanical processes involved in chemical reactions, it is essential to find a direct correspondence between experimental measurements and theoretical calculations. To achieve this goal, experimentalists need to select theoretically tractable molecules like H2 (N2, CO, etc.), which are also of relevance to current science. The researchers will prepare diatomic molecules in high vibrational states using a coherent optical technique called multi-step Stark-induced adiabatic Raman passage (multi-step SARP). Multi-step SARP is a generalization of the SARP process developed earlier by this research group, which can pump a large ensemble of H2 molecules to a variety of vibrationally excited levels. Multi-step SARP will combine two or more SARP processes to achieve near complete population transfer to a very highly vibrationally excited level. The researchers have shown theoretically that by combining several Stokes pulses on the wing of a stronger pump pulse it is possible to reach very high vibrational states. Long term prospects for this technique include preparing the highest vibrational level of H2 and even reaching the vibrational dissociation continuum, generating a pair of entangled loosely bound H atoms. These exotic quantum systems will allow the researchers to overcome the reaction barrier in cold and ultracold collisions and test fundamental quantum physics principles, such as interference in collision. The first goal of the project is to set up the multi-step SARP experiment and demonstrate the preparation of very high vibrationally excited levels of H2. Selection of the laser polarization used in the multi-step SARP will permit control of the alignment of the bond axis of the highly vibrationally excited molecules. Excitation of very high vibrational states using a two-step SARP process will be a major leap forward in the study of cold molecular collisions. Once prepared the researchers will carry out cold scattering experiments on the four-center reaction H2 + D2 →2HD in a supersonically expanded mixed beam of H2 and D2. The collision dynamics of highly vibrationally excited H2 molecules are of immense interest for understanding and modelling the physics and chemistry of the interstellar medium. Additionally, high-lying vibrational levels of H2 are considered essential to the efficient generation of H- beams by dissociative attachment of low energy electrons, which has important applications in igniting a fusion reactor.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.