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

非技术性摘要：具有轨道角动量的光（也称为“涡旋光束”和“扭曲光”）由于在高分辨率成像和高带宽通信中的应用而引起了相当大的兴趣，但对扭曲光如何与固体物质相互作用知之甚少。本研究探讨使用扭曲光在奈米结构中产生新的“扭曲”量子电子激发。实验是通过用具有可调轨道角动量的光照射圆柱形纳米结构（如环和点）来进行的，以便激发、测量和控制扭曲的电子态。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一个新的服务学习课程在丹佛大学的学生将这些研究的想法到附近的初中和高中通过动手示范。技术摘要：本项目的目标是演示和测量未开发的轨道角动量（OAM）激活的半导体纳米结构的光学跃迁。实验在量子环、量子点和量子威尔斯阱上进行，以便：1.）通过研究透射光谱的OAM依赖性，证明不同的轨道状态被扭曲的光访问; 2）测量具有零空间重叠的畸变（OAM激发的）电子和空穴波函数的退相，包括改变质心和相对运动角动量之间的分布，这仅在OAM激发的情况下是可能的;以及3）利用OAM可调谐光泵浦控制轨道态的弛豫。这些实验是由新的多维光谱，其中OAM和波长同时解决。

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.