GaAs（001）衬底上高品质GaAs量子点纠缠光子源的生长和物性研究

Entangled photon source is a key component in quantum information science. An ideal entangled photon source should have several properties including on-demand generation, high entanglement fidelity, high indistinguishability, and high photon collection efficiency. At the same time it should be compatible with current industrial technologies. Compared to the low yield spontaneous parametric down-conversion technique, semiconductor quantum dots have demonstrated the potential to fulfill all the requirements and received extensive attention. However, till now the existing technologies of fabricating quantum dot entangled photon sources all have their shortcomings such as very low probability of finding ideal dots, high fabrication cost, complicated tuning techniques and so on. This project intends to develop high quality entangled photon source using GaAs/AlGaAs quantum dots grown on the low-cost GaAs(001) substrate. Research topics of the project include the followings. (1) Elucidate the molecular beam epitaxy growth mechanism of highly symmetric GaAs/AlGaAs quantum dots on GaAs(001) substrate. (2) Theoretically analyze and calculate the enhancement of quantum dot emission rate and photon collection efficiency by optical cavity, especially by the micro-pillar optical cavity. Design optimized optical cavity according to predefined emission wavelength. (3) Study the influences of fabrication techniques on the optical properties of quantum dot emission and the physics behind them. To summarize, this project aims to explore the growth dynamics and fundamental device physics of GaAs/AlGaAs quantum dot based entangled photon source and to provide theoretical guidance and technical solutions for the development of high quality, low cost quantum dot based entangled photon source which at the same time does not need any external tuning.

纠缠光子源是量子信息科学的核心器件之一。理想的纠缠源应具备可确定性产生、高纠缠保真度、高全同性、高光子收集效率等品质，同时可与产业技术相兼容。半导体量子点因具有同时满足上述要求的潜力而受到广泛重视。但已有的几种量子点纠缠光子源制备技术均存在各自的不足，如找到理想量子点的几率低、成本高、技术复杂等。本项目拟开展基于低成本GaAs(001)衬底的高品质GaAs量子点纠缠光子源的研究。具体内容包括：（1）揭示分子束外延生长高对称性GaAs量子点的材料生长机制；（2）理论分析与计算光学腔，特别是微柱腔对量子点发光及光子收集效率的增强效应，设计针对特定波长的优化光腔；（3）研究器件制备技术对量子点光学品质的影响规律。本项目旨在探索高品质GaAs量子点纠缠光子源的材料生长动力学原理和基础器件物理，为发展不经任何外部调控即可发射纠缠光子对的高品质量子点纠缠光子源提供理论指导和技术方案。

本项目研究主要分三部分进行。第一部分是通过优化分子束外延生长条件得到高对称性的量子点。第二部分是设计适用于纠缠光子源的高收集效率光学微腔。第三部分是结合以上两点并经微纳加工，获得高品质的量子点纠缠光子源和适用于集成量子光学的器件样品。.通过本项目的支持，我们实现了：（1）具有较高对称性的GaAs/AlGaAs量子点，其平均精细结构分裂（FSS）为3-4μeV，最小的FSS<0.5μeV，证明量子点在形貌上有着较好的对称性。（2）设计了可以同时增强激子和双激子辐射的环形布拉格光栅光学微腔，其在宽谱范围内的收集效率可以高于90%。（3）我们实现了纠缠保真度达到90%，纠缠对产生的效率为59%，纠缠对提取效率为62%，光子的全同性为90%的高品质量子点纠缠光子源，性能为国际同期最优。我们同步研发了高品质的单光子源，并探索了量子光源在光量子信息中的应用。.此外，得益于本项目对分子束外延技术的提升，我们制备了高品质的大尺寸均匀超导金属薄膜样品，而且应用在超导量子计算方向研究中，制备了“祖冲之号”系列超导量子处理器，助推了我国超导量子计算优越性的实现。.整体来说，我们研制了高性能的量子器件，同时探索了其在量子信息的应用。