Fundamental Studies of Bose-Einstein Condensates of Polaritons

摘要：本课题研究低温下半导体结构中光学态的量子力学基本效应。该项目特别关注玻色-爱因斯坦凝聚（BEC）过程，其中许多粒子进入单个量子态。这里研究的BEC由“极化子”组成，它可以被视为具有特殊性质的光子；例如，它们有质量，像原子一样相互排斥。BEC在低温原子气体中得到了广泛的研究；这个关于极化子的BEC的项目通过提供观察系统的新方法来补充原子的BEC的研究。特别是，本项目所研究的系统发出像激光一样的相干光，可以使用先进的光学方法进行研究。该项目的首席研究员（PI）也将与匹兹堡的卡内基科学中心密切合作，向公众介绍量子力学的基本概念。技术摘要：本项目建立在前人成功的玻色-爱因斯坦极化子凝聚工作的基础上，主要实现三个目标：1)在匹兹堡大学进行实验，旨在建立平衡条件下BEC的相图，包括精确测定凝聚分数作为密度和温度的函数；2)匹兹堡大学的实验将研究准一维导线中BEC从“淬灭”（高度非平衡状态）一直到完全平衡的过程；3)匹兹堡大学的实验将研究环状凝聚物的宏观相干态，包括自旋织构和量子化角动量态。上述实验涉及超快时间分辨光谱学、成像和干涉测量方法，可在匹兹堡的Snoke实验室使用。对于这些推力，匹兹堡大学设计的样品在普林斯顿大学和滑铁卢大学通过分子束外延生长，然后送到匹兹堡大学在匹兹堡大学的洁净室进行最后的处理。该过程包括蚀刻结构，以制作用于控制极化子凝聚物流动的一维导线。这些实验的结果是与来自其他大学的理论家团队合作研究的，包括芝加哥大学、斯特拉斯克莱德大学、伍尔弗汉普顿大学和匹兹堡大学，以解决基本问题，如相互作用对冷凝物耗损的影响，平衡态冷凝物的阻尼理论，以及冷凝物的拓扑非平凡状态。该材料研究部（DMR）拨款支持研究，以了解平衡和非平衡条件下BEC的相图，资金来自DMR的凝聚态物理（CMP）计划和数学和物理科学（MPS）理事会物理部（PHY）的原子，分子和光学物理-实验（AMO-E）计划。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。

Nontechnical Abstract:This project studies fundamental effects of quantum mechanics of optical states in semiconductor structures at low temperature. In particular, this project focuses on the process of Bose-Einstein condensation (BEC), in which many particles enter a single quantum state. The BEC studied here is comprised of “polaritons,” which can be viewed as photons with special properties; for example, they have mass and repel each other, like atoms. BEC has been studied extensively in gases of atoms at low temperature; this project on BEC of polaritons complements the study of BEC of atoms by providing new ways of looking at the system. In particular, the system under study in this project emits coherent light like a laser, which can be studied using advanced optical methods. The principle investigator (PI) of the project will also work closely with the Carnegie Science Center in Pittsburgh to present basic concepts of quantum mechanics to the public. Technical Abstract:This project builds on previous successful work on Bose-Einstein condensation of polaritons by pursuing three main goals: 1) Experiments at the University of Pittsburgh will aim at establishing the phase diagram of BEC under equilibrium conditions, including accurate determination of the condensate fraction as a function of density and temperature; 2) experiments at the University of Pittsburgh will study the onset of BEC from a “quench” (a highly nonequilibrium state) all the way to full equilibrium, in quasi-one-dimensional wires; and 3) experiments at the University of Pittsburgh will study macroscopic coherent states of a condensate in a circular ring, including spin texture and quantized angular momentum states. The above experiments involve ultrafast time-resolved optical spectroscopy, imaging, and interferometry methods available in the Snoke laboratories in Pittsburgh. For each of these thrusts, samples designed at the University of Pittsburgh are grown by molecular beam epitaxy at Princeton University and at the University of Waterloo, then delivered to Pittsburgh for final processing in the clean room at the University of Pittsburgh. This processing includes etching the structures to make one-dimensional wires for controlling the flow of the polariton condensate. The results of these experiments are studied in collaboration with a team of theorists from other universities including the University of Chicago, the University of Strathclyde, the University of Wolverhampton, and the University of Pittsburgh to address fundamental questions, such as the effect of interactions on depletion of the condensate, the theory of damping of a condensate out of equilibrium, and topologically nontrivial states of a condensate.This Division of Materials Research (DMR) grant supports research to understand the phase diagram of BEC under equilibrium and non-equilibrium conditions with funding from the Condensed Matter Physics (CMP) Program in DMR and the Atomic, Molecular and Optical Physics - Experiment (AMO-E) program in the Division of Physics (PHY) both of the Mathematical and Physical Sciences (MPS) Directorate.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.