CAREER: Nonlinear Dynamics of Exciton-Polarons in Two-Dimensional Metal Halides Probed by Quantum-Optical Methods

在化学学部化学结构、动力学和机制A （CSDM-A）项目的支持下，维克森林大学的Ajay Ram Srimath Kandada正在将量子光学原理纳入超快非线性光谱学，以研究接近单光子激发极限的材料的光激发动力学。非线性光谱学被广泛用于探索光-物质相互作用，由于经典光学检测的基本限制，非线性光谱学需要高强度的光。不幸的是，这常常在导出的光物理模型中引入显著的模糊性。这个研究项目试图通过利用量子光学方法提供的优越的信噪比来克服这一限制。Srimath Kandada博士和他的学生将利用这种增强的实验能力来研究金属卤化物钙钛矿二维衍生物的独特激子物理。提高对钙钛矿光物理的理解有望推动其光电性能的优化，并为各种应用带来潜在的好处。教育和推广计划以研究计划的光学和光谱部分为中心，将在维克森林大学和当地高中的学生和教师之间建立协同合作伙伴关系，以激励来自不同背景的学生更多地参与STEM（科学、技术、工程和数学）教育和研究。本研究项目旨在测量激子-晶格相关的动力学和驱动激子-晶格相关的波动，准确估计激子和激子间相互作用的本征减相率，并在没有多体贡献的情况下测量载流子热化和激子形成的动力学。该项目的第一部分将集中在二维金属卤化物中光激发的极化耦合的性质和动态晶格波动的作用。该实验包括测量在脉冲产生的相干声子群存在的瞬态光学响应的振幅和相位中的噪声。这将能够估计随机晶格波动对声子非调和性和激子的极化修饰的贡献。该项目的第二部分将使用量子纠缠光子作为多体激子动力学的探针。通过共振介质传输的一对光谱纠缠光子之间的能量相关性将用于准确估计激子脱相率和双激子相互作用，从而消除了多阶展开问题。在一个经典的泵浦-量子探针实验中，光子纠缠也被用来测量极低激发密度下激子的居群动力学。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 Structure, Dynamics, and Mechanisms A (CSDM-A) program in the Division of Chemistry, Ajay Ram Srimath Kandada of Wake Forest University is incorporating quantum-optical principles into ultrafast nonlinear spectroscopy to investigate photo-excitation dynamics in materials close to the single-photon excitation limit. Nonlinear optical spectroscopy, which is widely used to explore light-matter interactions, requires high light intensities due to fundamental limitations in classical optical detection. Unfortunately, this often introduces significant ambiguity in the derived photophysical models. This research project seeks to overcome this limitation by harnessing the superior signal-to-noise ratio provided by quantum-optical methods. Dr. Srimath Kandada and his students will use this enhanced experimental capability to investigate the unique exciton physics of two-dimensional derivatives of metal halide perovskites. Improved comprehension of perovskite photophysics is expected to drive the optimization of their optoelectronic properties, with potential benefits for a variety of applications. The education and outreach program, centered on the optics and spectroscopy components of the research program, will build a synergistic partnership between the students and faculty at Wake Forest University and the local high schools to motivate greater participation of students from diverse backgrounds in STEM (science, technology, engineering and mathematics) education and research.This research project aims to measure the dynamics of exciton-lattice correlations and the fluctuations that drive them, to accurately estimate the intrinsic dephasing rate of excitons and inter-exciton interactions and to measure the dynamics of carrier thermalization and exciton formation without many-body contributions. The first part of the project will focus on the nature of polaronic coupling of photo-excitations in two-dimensional metal halides and the role of dynamic lattice fluctuations. The experiment involves the measurement of noise in the amplitude and phase of the transient optical response in the presence of an impulsively generated population of coherent phonons. This will enable the estimation of contributions from stochastic lattice fluctuations to the phonon anharmonicity and polaronic dressing of excitons. The second part of the project will employ quantum-entangled photons as a probe of many-body exciton dynamics. The energy correlations between a pair of spectrally entangled photons, transmitted through the resonant medium, is to be used to accurately estimate exciton dephasing rate and biexciton interactions, bereft of multi-order expansion issues. The photon entanglement is also to be exploited to measure the population dynamics of excitons at extremely low excitation densities in a (classical) pump - (quantum) probe experiment.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.