Quantum dynamics of two-body, few-body and many-body molecular systems at low temperatures

本研究计划旨在探索电磁场中二元、少体和多体分子系统的量子动力学。具体而言，拟开展的研究将集中在三个方面：(i)复杂多原子分子的低温动力学和受控化学；（ii）新相互作用体系中的极化子；（三）开放量子系统中受控的能量传递。在这些主题中，我们将解决当前物理和化学研究前沿最紧迫的问题，并且只考虑已经或即将通过实验实现的分子系统。研究方向(i)的目标是研究缓冲气体将碳氢化合物分子冷却到亚开尔文温度的可行性，并开发工具来探索冷分子在电磁场中双分子化学反应的独特特征。这项工作将与分子缓冲气体冷却实验密切相关，缓冲气体冷却实验是一个新兴的研究方向，旨在为痕量分子的灵敏检测和在实验室框架内缓慢运动的多原子分子的高通量光束的产生创造新技术。主题（ii）和（iii）的研究是由最近引人注目的实验所激发的，这些实验证明了在低于1微开尔文的温度下合成分子的可能性。人们发现，超冷分子的反应性很强，能以很快的速度进行化学反应。还证明了超冷分子可以被捕获在光学晶格的周期势中。目前的实验重点是提高捕获保真度，以尽量减少无序的影响，努力产生一个周期性的晶体状系统，其中分子被激光场势悬浮，分子间的相互作用可以被电磁场控制。我们将研究被困在激光场中的极化子哈密顿子的实现。极化子是出现在粒子（如电子或激子）与玻色子场（如声子）耦合的激发谱中的准粒子。我们将在粒子场相互作用参数范围内计算极化子的相图，并研究在冷分子的激发光谱中观察非线性极化子相互作用的可能性。我们将开发计算机代码来研究在光学晶格中捕获分子的受控开放量子系统实验实现的可行性。目标将是提出一个实验系统，可用于研究(a)在马尔可夫和非马尔可夫环境之间的过渡附近耦合到有限大小浴的量子粒子的动力学；(b)具有可控、有限尺寸槽的开放量子系统中能量输运的控制机制。如果我们的研究结果表明复杂的有机分子可以被冷却到超冷的温度，那么冷分子的研究领域将会大大扩展。在不远的将来，研究具有生物学意义的隧道反应将有可能不需要热平均以及许多尚未研究的基本现象。例子包括化学动力学中几何相位和可调谐共振的影响，精细结构对化学转化的影响以及量子统计在化学反应性中的作用。我们对新型极化子问题的研究将以新的方式连接分子光谱和凝聚态物理，为这两个研究领域提供新的刺激。捕获分子的可控开放系统的实现可能成为耗散下少粒子动力学研究的新范式。

Funding is requested for a theoretical research program that will explore quantum dynamics of binary, few-body and many-body molecular systems in electromagnetic fields. Specifically, the proposed research will be on three topics: (i) low-temperature dynamics of complex polyatomic molecules and controlled chemistry; (ii) polarons in new interaction regimes; and (iii) controlled energy transfer in open quantum systems. Within each of these topics, we will address the most pressing questions at the forefront of current research in physics and chemistry and only consider molecular systems that have been or can soon be experimentally realized. The goal of research direction (i) will be to study the feasibility of buffer gas cooling of hydrocarbon molecules to subKelvin temperatures and to develop tools to explore the unique features of bimolecular chemical reactions of cold molecules in electromagnetic fields. This work will be closely related with the experiments on buffer gas cooling of molecules, an emerging research direction aiming to create new technologies for sensitive detection of trace molecules and the production of high-flux beams of polyatomic molecules slowly moving in the laboratory frame. The research of topics (ii) and (iii) is motivated by the spectacular recent experiments which demonstrated the possibility of synthesizing molecules at temperatures below 1 microKelvin. It was found that ultracold molecules can be very reactive, undergoing chemical reactions at fast rates. It was also demonstrated that ultracold molecules can be trapped in a periodic potential of an optical lattice. Current experiments are focused on improving the trapping fidelity to minimize the effect of disorder, in an effort to produce a periodic, crystal-like system, where molecules are suspended by the laser field potential and intermolecular interactions can be controlled by electromagnetic fields. We will study the realization of the polaron Hamiltonians with molecules trapped in laser fields. Polarons are quasi-particles appearing in the excitation spectra of particles (such as electrons or excitons) coupled to a bosonic field (such as phonons). We will calculate the phase diagram of polarons in the previously unexplored range of particle - field interaction parameters and study the possibility of observing non-linear polaron interactions in the excitation spectra of cold molecules. We will develop computer codes to study the feasibility of the experimental realization of controlled open quantum systems with molecules trapped in optical lattices. The goal will be to propose an experimental system that could be used to study (a) the dynamics of quantum particles coupled to a finite-size bath near a transition between the Markovian and non-Markovian environment; and (b) control mechanisms of energy transport in open quantum systems with controllable, finite-size baths. If our results show that complex organic molecules can be cooled to ultracold temperatures, the research field of cold molecules will greatly expand. Within reach will be the possibility to study tunnelling reactions of biological interest without thermal averaging as well as many fundamental phenomena that cannot yet be studied. Examples include effects of the geometric phase and tunable resonances in chemical dynamics, effects of fine structure on chemical transformations and the role of quantum statistics, or lack thereof, in chemical reactivity. Our study of novel polaron problems will connect molecular spectroscopy and condensed-matter physics in new ways, providing a new stimulus to both research fields. The realization of controllable open systems with trapped molecules may become a new paradigm in the study of few-particle dynamics under dissipation.