Ultrafast Imaging of Molecular Polariton Transport: Competition between Coherence and Localization

分子极化子传输的超快成像：相干性和定位之间的竞争

• 批准号: 2154388
• 负责人: Libai Huang
• 金额: $ 48万
• 依托单位: Purdue University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-07-01 至 2025-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2154388&HistoricalAwards=false
• 关键词: Ultrafast; Imaging; Molecular; Polariton; Transport

With support from the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) Program in the Division of Chemistry, Professor Libai Huang and her research group at Purdue University are studying new ways to use light to control the transfer of energy between confined molecules. The project uses light trapped between a pair of very closely spaced mirrors to control the migration of energy between the molecules. Recent developments demonstrate that millions of molecules can collectively interact with a single mode of light when they are placed in a properly designed cavity. Although the molecules normally act like independently oscillating pendula (representing excited electron-hole pairs called excitons), the interaction with light inside the cavity results in a correlated motion of the pendula as if they are all attached to a single driving rod. When the energy exchange rate between the photons and the excitons (i.e., the light and the pendula) is faster than other energy loss pathways, new quantum states known as polaritons are formed with mixed light-matter characteristics. Polaritons have a low effective mass that allows the energy to travel at an extremely high speed, many orders of magnitude faster than the excitons alone. Thus, polaritons have the potential to enhance the speed of energy migration in molecular materials. However, the polariton states are very fragile and short-lived because the synchronization of millions of molecules can be easily disrupted. When the coherence is disrupted, energy becomes localized on a few molecules instead of being shared by millions of molecules. Understanding the competition between coherence and localization holds the key to harnessing the power of polaritons. The research team led by Prof. Huang is addressing this scientific challenge by developing microscopy techniques to record the propagation of polaritons with a resolution of 15 femtoseconds (a femtosecond is one quadrillionth of a second) and of 50 nanometers (a nanometer is one-billionth of a meter). The team also images the direction of propagation to differentiate polariton and exciton contributions. The research activities are integrated with K-12, undergraduate, and graduate science education. Specific educational and outreach activities include developing an undergraduate-level quantum chemistry lab module on strong light-matter coupling and partnering with the Superheroes of Science YouTube channel to make short videos for K-12 students and the general public on topics related to the research. Strong coupling between molecular excitons and cavity photons provides a new paradigm for achieving long-range coherent energy transport. A single mode of light can collectively interact with millions, or even billions, of molecules to form macroscopically coherent light-matter hybrid states known as polaritons. The formation of polaritons can dramatically alter the energy landscape and dynamics of the molecules. The photonic nature of polaritons enables fast propagation and long-range delocalization, which are beneficial for enhancing exciton transport. However, challenges remain in exploiting strong light-matter interactions for long-range energy transport in molecular systems, due to the inherent inhomogeneities and large vibronic coupling that result in ultrafast dephasing, a high density of dark states, and disorder-induced localization. This project aims to develop ultrafast microscopy tools in both real- and Fourier-space to provide a comprehensive picture of the competition between coherent polariton transport and decoherence processes in molecular aggregates. The measurements probe the transport of molecular polaritons with simultaneously high spatial (~50 nm) and temporal (~15 fs) resolution as well as momentum selectivity by combining ultrafast pump-probe microscopy with Fourier filtering. Molecular aggregates in Fabry-Perot microcavities with tunable Rabi splitting are used to investigate the role of vibronic coupling, disorder, and dark states in the transition from coherent to diffusive transport regime, as well as the direct visualization of remote energy transfer on macroscopic length scales resulting from the collective coherence. Beyond the fundamental insights made possible by these measurements, comparison with quantum chemistry calculations in collaboration with theory groups provides valuable information to aid the development of quantum mechanical theories for modeling molecular polaritons. The broader impacts of the project are further enhanced through educational and outreach activities that make the research accessible to a wide audience.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.

在化学结构，动力学和机制-A（CSDM-A）计划的支持下，Libai Huang教授及其普渡大学的研究小组正在研究使用光线来控制限制分子之间能量传递的新方法。该项目使用被困在一对非常紧密的镜子之间的光来控制分子之间能量的迁移。最近的发展表明，当将它们放置在正确设计的腔中时，数以百万计的分子可以集体与单一的光模式相互作用。尽管该分子通常像独立振荡的摆（代表令人兴奋的电子孔对称为激子）一样，与光内部的光相互作用会导致钟摆的相关运动，就好像它们都连接到单个驱动棒一样。当照片和激子之间的能量汇率（即，光和吊灯）比其他能量损耗途径快时，形成了具有混合的光 - 质体特性的新量子状态。极性子的有效质量较低，可以使能量以极高的速度传播，比单独的激子更快。这是极性子有可能提高分子材料中能量迁移的速度。但是，北极状态非常脆弱且短暂，因为数百万分子的同步很容易被破坏。当相干性被破坏时，能量就会局限于几个分子，而不是被数百万分子共享。了解连贯性和本地化之间的竞争是利用极化人的力量的关键。由黄教授领导的研究团队正在通过开发显微镜技术来解决这一科学挑战，以记录以15个飞秒的分辨率（飞秒为四十四秒的一秒钟）和50纳米的北极子的传播（纳米计为米的一千万米三分之一）。该团队还为分化极化和令人兴奋的贡献的传播方向形象。研究活动与K-12，本科生和研究生科学教育融为一体。特定的教育和外展活动包括开发一个本科级别的量子化学实验室模块，以强烈的轻度耦合以及与科学YouTube频道的超级英雄合作，为K-12学生和公众在与研究有关的主题上制作简短的视频。分子激子和空腔照片之间的强耦合为实现长距离连贯的能量传输提供了新的范式。单一的光模式可以与数百万甚至数十亿分子共同相互作用，形成称为北极子的宏观一致的光晶状体。极化子的形成可以动态地改变分子的能量景观和动力学。极化子的光子性质可实现快速传播和远程离域化，这有助于增强令人兴奋的运输。然而，由于固有的不均匀性和较大的振动耦合，挑战在分子系统中的远程能量传输中仍然存在挑战，从而导致超快倾向，高密度的黑暗状态以及无序诱导的定位。该项目旨在在实地和傅立叶空间中开发超快速显微镜工具，以全面了解分子聚集体中相干极化传输与破坏性过程之间的竞争。测量结果通过将超快泵送显微镜与傅立叶滤波相结合，探测了具有简单的高空间（〜50 nm）和临时（〜15 fs）分辨率以及动量选择性的分子偏振子的传输。具有可调狂犬分裂的Fabry-Perrot微腔中的分子聚集体用于研究振动耦合，混乱和暗状态在从相干到分化转运方案的过渡中，以及远程能量转移在巨镜长度尺度上的直接可视化。除了这些测量结果使与理论组合作的量子化学计算相比，与量子化学计算相比，除了基本的见解之外，还提供了有价值的信息，以帮助开发量子机械理论来建模分子极化子。通过教育和外展活动，该项目的广播公司影响进一步增强，这使广泛的受众群体可以访问研究。该奖项反映了NSF的法定任务，并使用基金会的知识分子优点和更广泛的影响审查标准，认为通过评估而被认为是珍贵的支持。

项目成果

Enhanced Two-Dimensional Exciton Propagation via Strong Light–Matter Coupling with Surface Lattice Plasmons

• DOI: 10.1021/acsphotonics.3c00466
• 发表时间: 2023-05
• 期刊: ACS Photonics
• 影响因子: 7
• 作者: Linrui Jin;Alexander D. Sample;Dewei Sun;Yao Gao;Shibin Deng;Ran Li;L. Dou;Teri W. Odom;Libai Huang