Measuring Electronic Coherence at the Single-Molecule Level with Nonlinear Coherent Spectroscopy

在化学系化学测量和成像（CMI）项目的支持下，密歇根州立大学的Elad Harel博士和他的研究小组正在开发测量单分子量子力学行为的新方法。在量子力学中，分子的行为通常取决于系统不同状态之间的微妙关系。这种关系称为相干性，很容易通过与周围环境的相互作用而被破坏，并且通常需要实验学家在低温或高度隔离的环境中进行困难的测量，以探测复杂系统的量子力学性质。然而，越来越清楚的是，即使在环境条件下，量子力学在分子系统的行为中也起着重要作用，包括将阳光转化为化学能的光合蛋白质。虽然已经测量了分子集合的相干性，但了解单个分子的行为对于理解分子结构如何影响复杂系统的功能非常重要。因此，Harel教授的团队正在开发工具，通过采用极其灵敏的检测方法来测量单分子水平的相干性。该研究项目还为学生提供先进的技术培训，并针对来自各种经济和社会背景的广大青年开展外联活动。在单分子水平上开发非线性光谱方法有望揭示目前无法通过集成方法获得的重要信息。在这个项目中，Harel博士和他的团队正在开发新的方法，以实现在室温下的单分子非线性光谱测量。该方法使用二维电子光谱探测电子相干性和电子振动耦合在单分子水平。这些测量揭示了复杂系统中重要的结构-功能-动力学关系，包括环境条件下的色素-蛋白质复合物和量子限制纳米晶体。了解真正的电子相干时间和它的物理起源自由的非均匀加宽是至关重要的比较实验测量与理论预测，并为发展更深层次的分子相互作用的基本理解。研究小组正在开发的新方法有可能影响对控制各种复杂化学系统的分子机制的理解。除了使重要的分子系统的新的测量，该项目的研究目标是紧密结合在研究生和本科生水平的学生培训，包括一个让研究生发展五个-该奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的评估支持影响审查标准。

With support from the Chemical Measurement and Imaging (CMI) Program in the Division of Chemistry, Dr. Elad Harel and his research group at Michigan State University are developing new methods to measure the quantum mechanical behavior of single molecules. In quantum mechanics, the behavior of a molecule often depends on a delicate relationship between the different states of the system. This relationship, called coherence, is easily disrupted through interactions with the surrounding environment, and often requires experimentalists to make difficult measurements at low temperatures or in highly isolated environments in order to probe the quantum mechanical properties of a complex system. However, it is becoming increasingly clear that even under ambient conditions quantum mechanics plays an important role in the behavior of molecular systems, including photosynthetic proteins that convert sunlight into chemical energy. While coherence has been measured for collections of molecules, knowing the behavior of single molecules is important for understanding how molecular structure affects the function of complex systems. Therefore, Professor Harel’s team is developing tools to measure coherence at the single-molecule level by employing extremely sensitive detection methods. The research project also provides advanced technical training for students, as well as outreach activities targeting a wide audience of young people from a range of economic and social backgrounds.The development of nonlinear spectroscopy methods at the single-molecule level holds the promise of revealing important information that is not currently available from ensemble methods. In this project, Dr. Harel and his group are developing new methods to enable single-molecule nonlinear spectroscopy measurements at room temperature. The approach uses two-dimensional electronic spectroscopy to probe electronic coherences and electronic-vibrational coupling at the single-molecule level. These measurements reveal important structure-function-dynamics relationships in complex systems, including pigment-protein complexes and quantum-confined nanocrystals under ambient conditions. Understanding the true electronic coherence time and its physical origin free of inhomogeneous broadening are critically important for comparing experimental measurements with theoretical predictions, and for developing a deeper fundamental understanding of molecular interactions. The new approach being developed by the research team has the potential to impact understanding of molecular mechanisms that govern a wide range of complex chemical systems. In addition to enabling important new measurements of molecular systems, the research goals of the project are closely integrated with student training at the graduate and undergraduate levels, including a program in which graduate students develop five-week summer tutorial courses based on their research.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.