Donor Electron Spins in Direct Bandgap Semiconductors for Quantum Networks

量子信息网络有望在优化问题的计算、加密破解、材料模拟等方面取得突破，并从根本上实现安全通信。晶体中的量子缺陷已经显示出实现可扩展量子网络所需的一些特征；然而，找到一个同时展示所有必要的光学和量子特性的系统仍然具有挑战性。基于有希望的初步结果，氧化锌（ZnO）中的单供体缺陷可能满足这些标准。本项目旨在展示单氧化锌供体的产生和检测，并完全控制和表征供体电子和原子核。目标是确定该系统在可扩展量子信息应用中的前景。此外，氧化锌中单一供体杂质的研究可能会导致研究半导体掺杂剂的新技术，并将培养量子光学和纳米技术领域的研究生和本科生，为他们在国家实验室、工业和学术界的职业生涯做好准备。基于缺陷的量子信息处理由于具有器件集成的潜力、自旋光子转移的可能性以及高纯度晶体中的长量子相干时间而具有吸引力。对于具有光辐射的缺陷系统，基于测量的协议可用于在非相互作用、远程分离的量子比特之间创建量子网络。本项目将研究具有良好光学性质的缺陷体系，即ZnO中的施主体系，该体系在零声子线具有均匀的光学跃迁和接近统一的辐射效率。先前的研究表明，如果同位素纯化的ZnO晶体可用，供体系统的相干时间可能会很长。本文将采用不同的技术来分离单个供体：生长小直径的单氧化锌纳米线，以及纳米级掩蔽或聚焦离子束蚀刻结合低供体密度的外延氧化锌层。单个供体的隔离将通过光子自相关测量得到证实。光泵浦和微波脉冲用于高保真相干控制将用于研究单一ZnO供体的光学和自旋（电子和核）相干性，测试该系统作为量子比特候选者的适用性。由于施主的有效质量性质，有可能将ZnO中的量子特性推广到直接带隙半导体中的整个施主类别，从而进一步促进本研究的影响。该项目由数学和物理科学理事会物理部量子信息科学（QIS）项目、数学和物理科学理事会材料科学部凝聚态物理（CMP）项目以及工程理事会电气、通信和网络系统部电子、光子学和磁性器件（EPMD）项目共同资助。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。

Quantum information networks are expected to enable breakthroughs in computation for optimization problems, encryption-breaking, and materials simulation, as well as realize fundamentally secure communication. Quantum defects in crystals have been shown to exhibit some of the characteristics needed to realize a scalable quantum network; however finding a system that simultaneously exhibits all of the requisite optical and quantum properties remains challenging. Based on promising preliminary results, single donor defects in zinc oxide (ZnO) may satisfy these criteria. This project is to demonstrate single ZnO donor creation and detection with complete control and characterization of the donor electron and nucleus. The goal is to determine the outlook of this system for scalable quantum information applications. In addition, the study of single donor impurities in ZnO may lead to new techniques for studying dopants in semiconductors and will train a diverse group of graduate and undergraduate students in quantum optics and nanotechnology, preparing them for careers in national laboratories, industry, and academia.Defect-based quantum information processing is attractive due to the potential for device integration, the possibility of spin-photon transfer, and the long quantum coherence time in high-purity crystals. For defect systems with optical radiation, measurement-based protocols can be utilized to create quantum networks between non-interacting, remotely separated qubits. This project will investigate a defect system with favorable optical properties, i.e. the donor system in ZnO, which has homogeneous optical transitions and near-unity radiative efficiency in the zero phonon line. Prior studies in an ensemble of donors showed the potential for long coherence times of the donor system if isotopically purified ZnO crystal is available. Here, different techniques will be utilized to isolate single donors: growth of single ZnO nanowires with small diameters, and nano-scale masking or focused ion beam etching combined with epitaxial ZnO layers of low donor density. The isolation of single donors will be confirmed by a photon autocorrelation measurement. Optical pumping and microwave pulses for high-fidelity coherent control will be used to study the optical and spin (electron and nuclear) coherence properties of single ZnO donors, testing the suitability of this system as a qubit candidate. Due to the effective mass nature of the donor, it may be possible to generalize the quantum properties found in ZnO to the entire class of donors in direct band gap semiconductors, furthering the impact of this research.This project is jointly funded by the Quantum Information Science (QIS) Program in the Physics Division in the Directorate for Mathematical and Physical Sciences, and the Condensed Matter Physics (CMP) Program in the Division of Materials Science in the Directorate for Mathematical and Physical Sciences, and the Electronics, Photonics and Magnetic Devices (EPMD) Program in the Division of Electrical, Communications and Cyber Systems Division in the Engineering 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.