Molecular Radiative and Relaxation Processes

加州大学欧文分校的Shaul Mukamel由化学系化学理论、模型和计算方法计划资助，研究开发用于分析分子吸收和重新分配光的精确方式的技术。这类过程发生在光合作用过程中。了解太阳能转化为化学能的准确方式有助于设计新的设备，人为地将光转化为更有用的能量形式。此外，对单个光子的探测，也就是与分子相互作用的光粒子，可以揭示组成这些分子的原子的结构和运动的大量信息。通过对分子施加一系列短光脉冲，研究人员正在寻找方法来提取有关该分子结构和功能的额外信息。更多的研究探索了纠缠光子的使用，这是一种非常有前途的量子计算工具，安全通信方法和其他可能的应用。可能有助于揭示生物细胞细节的新成像方法也在开发中。所有这些研究都是与其他研究人员合作进行的，他们设计的设备和实验用于测试这些理论研究揭示的见解。这项工作通过发展新的语言和概念对实验科学界产生了广泛的影响，这些语言和概念有助于指导科学家理解光与物质相互作用过程的基本性质。研究人员通过网络自由分享他们开发的软件。复杂分子对超快激光脉冲序列的反应提供了电子和振动动力学以及相互关系的多维视图。开发了用于设计、解释和分析这些信号的模型和计算工具。光的量子性质，如光子纠缠，作为探测分子和生色团聚集体的工具受到了特别的重视。在另一个项目中，通过精心设计的相干拉曼信号来研究非绝热动力学。受激拉曼信号中时间分辨率和光谱分辨率的相互作用正在被研究。然后，可以预测将单个光子的符合测量和干涉测量相结合的新的探测方案。涉及新的脉冲序列的实验技术正在设计中，用于分析它们的理论和计算工具正在开发和广泛应用。其中一些应用是在凝聚相中的复杂分子，半导体量子点中的激子，以及在光合作用天线和反应中心的光收集过程中的基本电荷和能量迁移过程。特别是，超级算符格林函数形式正在发展，它允许计算分子对量子光和随机光的响应。利用纠缠和压缩光子的新光谱信号提供了经典光不可能提供的时间和光谱分辨率。这些技术正被应用于分子聚集体中激子的研究。作为一种新的光谱工具，还探索了测量与分子相互作用对光子统计的影响。人们正在研究利用荧光对相干信号进行非相干检测，从而实现对单分子的研究。利用脉冲整形、相位控制和分子手性，发展了一种高度直观的回路图表示法来设计脉冲序列。广义信号涉及几个脉冲激励和测量的组合，可以探测经典和量子系统在稳态时的响应和自发涨落，并与非线性涨落定理相联系。用复合玻色子(共玻色子)代数表示描述和计算具有多个电子和空穴粒子的激发态的新的多体方法正在发展中。因此，这种新方法避免了预测非线性信号所需的繁琐的多激子波函数的显式计算。

Shaul Mukamel of the University of California, Irvine is funded by the Chemical Theory, Models and Computational Methods program in the Chemistry division for research to develop techniques that are used to analyze the precise ways molecules absorb and redistribute light. This type of process happens during photosynthesis. Understanding the precise ways that solar energy is converted to chemical energy can help in the design of new devices which artificially convert light to more useful forms of energy. In addition, the detection of individual photons, particles of light which have interacted with molecules, can reveal a great deal of information about the structure and motion of the atoms which make up those molecules. By applying a series of short light pulses to a molecule, the investigators are finding ways to extract additional information about that molecule's structure and function. Additional research explores the use of entangled photons, a very promising tool for quantum computing, secure communication methods and other possible applications. New imaging methods that might be helpful in revealing the details of biological cells are also being developed. All of these studies are carried out in collaboration with other investigators who design equipment and experiments that are used to test the insights revealed by these theoretical studies. The work has a broad impact on the experimental science community through the development of new language and concepts that help to guide scientist's understanding of the fundamental nature of the process by which light interacts with matter. The investigators freely share the software they develop through the web.The response of complex molecules to sequences of ultrafast optical laser pulses provides a multidimensional view of electronic and vibrational dynamics and of correlations. Models and computational tools are developed for the design, interpretation and analysis of these signals. Quantum properties of light, such as photon entanglement, receive special consideration as tools for probing molecules and chromophore aggregates. In another project, nonadiabatic dynamics is studied by carefully designed coherent Raman signals. The interplay of temporal and spectral resolution in stimulated Raman signals is being investigated. New detection schemes that combine coincidence measurements of individual photons and interferometry can then be predicted. Experimental techniques involving novel pulse sequences are being designed, and theoretical and computational tools for their analysis are developed and broadly applied. Some of the applications are to complex molecules in the condensed phase, to excitons in semiconductor quantum dots, and to the elementary charge and energy migration processes in light harvesting in photosynthetic antennae and reaction centers.In particular, superoperator Green's function formalism is being developed that allows the computation of the response of molecules to both quantum and stochastic light. New spectroscopic signals that make use of entangled and squeezed photons offer temporal and spectral resolutions not possible with classical light. These techniques are being applied to the study of excitons in molecular aggregates. Measurements of the effect of interactions with molecules on photon statistics are also explored as a novel spectroscopic tool. Incoherent detection of coherent signals by fluorescence which can allow the study of single molecules is being investigated. A highly-intuitive loop diagram representation is developed for the design of pulse sequences by utilizing pulse shaping, phase control and molecular chirality. Generalized signals involving the combination of several impulsive excitations and measurements that can probe both the response and spontaneous fluctuations in classical and quantum systems at steady states are predicted and connected to nonlinear fluctuation theorems. New many-body approaches for describing and calculating excited states with multiple electron and hole particles are being developed using a composite Boson (co-boson) algebraic representation. The tedious explicit computation of multi-exciton wavefunctions usually required for predicting nonlinear signals is, thus, avoided with this new approach.