Understanding Emission, Absorption and Energy Transfer Involving Classical and Quantum Light Interacting with Molecules

在化学系化学理论、模型和计算方法项目的支持下，西北大学的George Schatz教授正在开发新的理论和计算方法来描述分子吸收和发射光时发生的过程。一个项目是关于在受激分子中能量转移到另一个分子的速率，在这个项目中，将发展理论，描述在供体分子中受激的电子将它们的能量转移到受体分子中的电子的过程。通过使用分子电子态相互作用的特殊模型，该理论可以将其他附近分子或纳米颗粒对能量传递过程的影响纳入其中，并在某些情况下导致提高速率或增加传递范围，这在许多光学器件中都很重要。研究的另一个组成部分是关于纠缠光子形式的量子光对光吸收的影响。在这里，时变量子理论被用来研究能量从光转移到电子（即将量子光转换为量子电子）时纠缠的演化。人们还在研究处于纠缠态的分子的性质，以了解它们的性质与处于非纠缠态的分子的性质有何不同。这项工作对基于光子的量子计算机和安全通信设备所涉及的技术至关重要。参与该项目的学生和博士后，包括相当数量的女性和少数民族，将接受理论发展和计算应用方面的培训，这些培训可以用于与新设备技术相关的学术和工业工作。此外，还将向K-12团体、本科培训、众多研讨会和讲习班以及与公众的交流进行推广。根据该奖项，George Schatz教授和他的团队将开发以下理论和计算方法：(1)使用实时电子结构方法描述分子之间的单光子共振能量转移；(2)表征分子电子（和振动）状态的纠缠特性，重点是由双光子吸收激发的状态；(3)建立双纠缠光子激发分子的时域描述，将量子电动力学与电子结构理论相结合，研究从光子到电子的纠缠演化，并使用称为纠缠见证的纠缠度量来表征。提出的研究解决了与复杂环境中经典光和量子光与分子相互作用有关的几个知识空白。利用实时电子结构方法进行能量传递提供了描述由附近分子或纳米颗粒介导的能量传递的机会。对于涉及纠缠光子的量子光，最近已经证明光子纠缠可以在某些问题上转化为电子纠缠，但其基本规则尚不清楚。拟议的研究将使用量子信息科学的概念来表征分子的电子纠缠特性，这些特性在双光子吸收中很重要，包括集体/施密特数和香农熵。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。

With support from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry, Professor George Schatz of Northwestern University is developing new theory and computational methods for characterizing processes that occur when molecules absorb and emit light. One project is concerned with the rate of transfer of energy in the excited molecule to another molecule, where theory will be developed that describes the process in terms of electrons excited in the donor molecule that transfer their energy to electrons in the acceptor molecule. By using a special model of interactions of electronic states of the molecules, the theory makes it possible to incorporate the influence of other nearby molecules or nanoparticles on the energy transfer process, and in some cases leading to enhanced rates or increased range of transfer, as is important in many kinds of optical devices. Another component of the research is concerned with the influence of quantum light in the form of entangled photons on the light absorption. Here time-dependent quantum theory is used to study the evolution of entanglement as energy transfers from light to electrons (i.e., converting quantum light to quantum electrons). Also being studied are the properties of molecules that are in the entangled states to understand how their properties are different from those in unentangled states. This work is fundamental to technologies involved in photon-based quantum computers and in devices for secure communications. The students and postdocs who work on this project, including a significant number of women and minorities, will be trained in theory development and computational applications that they can use for both academic and industrial jobs related to new device technologies. In addition, there will be outreach to K-12 groups, undergraduate training, numerous seminars and workshops, and communication with the public.Under this award, Professor George Schatz and his team will develop theories and computational methods for (1) describing single photon resonant energy transfer between molecules using real-time electronic structure methods, (2) characterizing the entanglement properties of molecular electronic (and vibronic) states, with emphasis on states that are excited by two-photon absorption, and (3) developing a time-domain description of the excitation of molecules by two-entangled photons that couples quantum electrodynamics to electronic structure theory to study the evolution of entanglement from photons to electrons as characterized using measures of the entanglement known as entanglement witness. The proposed research addresses several knowledge gaps that relate to the interaction of both classical and quantum light with molecules in complex environments. The use of real-time electronic structure methods for energy transfer provides the opportunity to describe energy transfer mediated by nearby molecules or nanoparticles. For quantum light that involves entangled photons, it has recently been demonstrated that photon entanglement can for some problems be converted into electronic entanglement, but the underlying rules for this are not known. The proposed research will use concepts from quantum information science to characterize the electronic entanglement properties of molecules that are important in two photon absorption, including collectivity/Schmidt numbers and Shannon entropy.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.