CAREER: Unlocking "forbidden" optical transitions in nanostructures using light with orbital angular momentum

非技术摘要：由于在高分辨率成像和高带宽通信中的应用，具有轨道角动量的光（也称为“涡旋光束”和“扭曲光”）最近引起了相当大的兴趣，但人们对扭曲光如何与固体物质相互作用知之甚少。这项研究探索了利用扭曲光在纳米结构中产生新的“扭曲”量子电子激发。实验是用具有可调轨道角动量的光来照亮圆柱形纳米结构，如环和点，以激发、测量和控制扭曲的电子状态。在这项研究中获得的新量子态可以用于未来的技术，如高带宽数据存储、计算和通信。此外，这项工作将被整合到丹佛大学的一门新的服务学习课程中，学生们将通过实践演示将这些研究想法带到附近的初中和高中。技术摘要：本项目的目的是演示和测量半导体纳米结构中未探索的轨道角动量（OAM）激活的光学跃迁。在量子环、量子点和量子阱上进行实验，目的是：通过研究透射光谱与OAM的关系，证明扭曲光可以进入不同的轨道态；2)。测量零空间重叠的扭曲（OAM激发）电子和空穴波函数的消相，包括改变质心和相对运动角动量之间的分布，这只有在OAM激发下才能实现；和3)。用oam可调谐光泵浦控制轨道态弛豫。这些实验是由一种新的多维光谱技术实现的，其中OAM和波长同时被分解。

Nontechnical abstract: Light with orbital angular momentum (also called "vortex beams" and "twisted light") has generated considerable recent interest because of applications in high-resolution imaging and high-bandwidth communications, but little is known about how twisted light interacts with solid matter. This research explores the use of twisted light to generate new "twisted" quantum electron excitations in nanostructures. Experiments are performed by illuminating cylindrical nanostructures such as rings and dots with light that has tunable orbital angular momentum in order to excite, measure, and control twisted electronic states. The new quantum states accessed in this research could be used in future technologies such as high-bandwidth data storage, computing, and communications. Additionally, this work will be integrated into a new service learning course at the University of Denver in which students will bring these research ideas into neighborhood middle and high schools through hands-on demonstrations.Technical abstract: The objective of this project is to demonstrate and measure unexplored orbital angular momentum (OAM)-activated optical transitions in semiconductor nanostructures. Experiments are performed on quantum rings, dots and wells in order to: 1.) Demonstrate that different orbital states are accessed with twisted light by studying the OAM dependence of transmission spectra; 2.) Measure the dephasing of distorted (OAM-excited) electron and hole wavefunctions with zero spatial overlap, including varying the distribution between center-of-mass and relative-motion angular momentum that is only possible with OAM excitation; and 3.) Control the relaxation of orbital states with OAM-tunable optical pumping. These experiments are enabled by novel multidimensional spectroscopy in which both OAM and wavelength are simultaneously resolved.