Stochastic Path Integral Formalism and Applications to Coherent Energy Transfer

来自麻省理工学院的曹建树获得了化学学部化学理论、模型和计算方法项目的奖励。Cao和同事开发了新的理论和计算方法来分析光合系统中的相干能量传递。光合作用是将太阳能转化为生物质的生物过程。这个过程的第一步包括通过光收集复合物阵列捕获光子（光粒子）。这些光子激发复合物中的电子。这种激发能被转移到反应中心，随后转化为化学能。光合作用的能量传递过程具有显著的效率。有广泛的基础研究来了解这种效率的基础。本研究为人工光收集装置的优化设计提供了有益的见解。在过去，这些设计努力试图模仿光合作用，基于这样的想法，即激发能从色素分子通过分子能量阶梯向下跳跃，一次一个分子地转移到反应中心。然而，最近的实验证据揭示了量子相干和合作效应的关键作用。这些新发现提出了一些基本问题，启发了提出的理论和计算发展。在解决这些问题的同时，曹教授投入了大量的精力来培训他的学生和博士后同事，在麻省理工学院开放课程软件上编写新的课程材料供公众使用，并进一步开发一个开放的网站来分发模拟代码。量子相干性可以说是最微妙的量子力学效应，它没有简单的经典类比，而是衍射、干涉、离域和量子纠缠的根源。显然，大自然在光合系统的优化设计中利用了微妙的相干效应，有效地将光子转化为化学键。然而，目前尚不清楚相干效应如何促进光合作用中非常有效和强大的能量传递，以及如何正确定义、测量和控制量子相干性。为了解决这些问题，曹建树通过极化子理论、随机模拟和实验合作开发了一个积极的研究项目。具体而言，研究计划包括三个部分：(i)以量子相干性为中心的理论和概念问题；（ii）用于模拟相干激子动力学的统一随机形式；（三）在自然光合系统和人工能源装置中捕光结构的应用。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。

Jianshu Cao from the Massachusetts Institute of Technology is supported by an award from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry. Cao and coworkers develop new theoretical and computational methods to analyze coherent energy transfer in photosynthetic systems. Photosynthesis is the biological process that converts solar energy into biomass. The first step of this process involves the capture of photons (particles of light) by arrays of light-harvesting complexes. These photons excite electrons in the complexes. This excitation energy is transferred to the reaction center for subsequent conversion to chemical energy. The energy transfer process in photosynthesis exhibits remarkable efficiency. There is extensive basic research to understand the basis of this efficiency. This research provides useful insight into the optimal design of artificial light-harvesting devices. In the past, these design efforts attempted to mimic photosynthesis based on the idea that the excitation energy is transferred from pigment molecules to the reaction center by hopping down the molecular energy ladder, one molecule at a time. However, recent experimental evidence reveals a crucial role for quantum coherence and for cooperative effects. These new findings raise fundamental questions that inspire the proposed theoretical and computational developments. While addressing these questions, Prof. Cao devotes significant efforts to training students and postdoctoral associates in his group, compiling new course materials on MIT OpenCourseWare for public access, and further developing an open website for the distribution of simulation codes. Arguably the most subtle quantum mechanical effect, quantum coherence has no simple classical analog but lies at the root of diffraction, interference, delocalization, and quantum entanglement. Evidently, nature takes advantage of subtle coherence effects in the optimal design of photosynthetic systems to effectively convert photons into chemical bonds. It is, however, unclear how the coherence effects can facilitate the remarkably efficient and robust energy transfer in photosynthesis and how quantum coherence can be properly defined, measured, and controlled. To address these questions, Jianshu Cao develops an active research program by integrating polaron theory, stochastic simulations, and experimental collaborations. Specifically, the research plan consists of three components: (i) theoretical and conceptual issues centered on quantum coherence; (ii) a unified stochastic formalism for simulating coherent exciton dynamics; and (iii) applications to light-harvesting structures in natural photosynthetic systems and in artificial energy devices.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.