Trapped Polariton Condensates: Fundamental Optical Studies and Novel Fabrication Methods

****技术摘要****本项目重点研究半导体微腔中激子-极化子凝聚物这一新兴领域。世界各地的几个实验小组现在已经证明了激子-极化子的行为完全类似于玻色-爱因斯坦凝聚（BEC），包括量子化漩涡、双峰动量分布、超流体流动、约瑟夫森结振荡和线性Bogoliubov激发谱。我们在匹兹堡的团队也展示了BEC的行为，使用我们独特的方法利用施加应力创造了一个谐波电位陷阱。我们提出的工作将使用几种新的实验方法，包括稳定激光来减少波动，同时对极化子进行实空间和动量空间成像，以及条纹相机时间成像，并将使用具有世界纪录极化子寿命的新型超高q腔（包括我们目前的结构，其q因子超过一百万，扩散长度为数百微米）。这项工作是与普林斯顿大学的L. Pfeiffer的制造小组合作的；我们将开发新型结构，包括蚀刻特征，作为极化的障碍。该项目将支持两名博士生学习现代光学的前沿方法，包括超快和非线性光学，设计和制造方法。研究无激光产生光相干的系统的基本物理，可能会导致新型相干光源、新的导光方法和光开关方法。****非技术摘要****相干光是没有随机“噪声”的光：你可以把相干光源想象成纯音的钟发出的声音，而非相干光则有随机噪声，就像没有调到广播电台的收音机发出的声音。大多数人都熟悉激光，它通过量子力学预测的特殊过程产生相干光。在过去的几年里，世界上几个实验室的研究人员，包括我们的实验室，已经开发出一种新型的固态系统，它通过一种完全不同的过程产生相干光。这种方法包括让固体内部的电子进行相干运动；电子的量子力学波动特性被用来使电子一起相位振荡，并且这些电子的辐射导致相干光发射。这种产生相干光的新方法已经被证明比常规激光更有效，而且还发现了其他一些新效应，比如光的漩涡。这个项目将研究这种令人着迷的新型光学系统的基本物理学，被称为玻色-爱因斯坦极化子凝聚。研究生将接受训练，使用时间分辨率小于万亿分之一秒的尖端光学方法，他们将研究这些固态结构的新设计，这些结构需要几纳米（即十亿分之一米）的尺寸。这种类型的设备最终可能用于光通信，在万亿分之一秒内打开和关闭光，在相同的时间尺度上将光引导到不同的通信通道，并制造高效的相干光发射器。

****Technical abstract****This project focuses on the new and growing field of exciton-polariton condensates in semiconductor microcavities. Several experimental groups around the world have now shown behavior of exciton-polaritons which is exactly analogous to Bose-Einstein condensation (BEC), including quantized vortices, a bimodal momentum distribution, superfluid flow, Josephson junction oscillations, and linear Bogoliubov excitation spectra. Our group in Pittsburgh has also shown BEC behavior, using a harmonic potential trap created using our unique method using applied stress. Our proposed work will use several new experimental methods, including stabilized lasers to reduce fluctuations, simultaneous real-space and momentum-space imaging of the polaritons, and streak camera temporal imaging, and will use new ultra-high-Q cavities with world record polariton lifetimes (including our present structures which have Q-factor of over a million and diffusion lengths of hundreds of microns). This work is in collaboration with the fabrication group of L. Pfeiffer at Princeton; we will develop new types of structures including etched features acting as barriers for the polaritons. The project will support two Ph.D. students to learn cutting-edge methods of modern optics, including ultrafast and nonlinear optics, design, and fabrication methods. Research on the basic physics of systems generating optical coherence without lasing, may lead to new types of coherent light sources, new methods of light guiding, and new optical switching methods.****Non-technical abstract****Coherent light is light that has no random "noise": you can think of a coherent light source as like the sound from a bell with a pure tone, while incoherent light has random noise, like the sound of a radio tuned to no radio station. Most people are familiar with lasers, which generate coherent light via a special process predicted by quantum mechanics. In the past few years, researchers at several labs around the world, including ours, have developed a new type of solid-state system which generates coherent light by an entirely different process. This method involves getting the electrons inside a solid to act coherently; the quantum mechanical wave nature of the electrons is used to make the electrons oscillate in phase together, and the radiation from these electrons leads to coherent light emission. This new method of generating coherent light has already been shown to be more efficient than regular lasing, and several other novel effects have been seen such as vortices of light. This project will study the basic physics of this fascinating new type of optical system, known as Bose-Einstein condensation of polaritons. Graduate students will be trained to use cutting-edge methods of optics with time resolution of less than a trillionth of a second, and they will work on new designs of these solid-state structures, which require structures with dimensions of a few nanometers, i.e., billionths of meters. This type of device may eventually be used in optical communications to switch light on and off in trillionths of seconds, to direct light into different communications channels on the same time scales, and to make efficient coherent light emitters.