Donor Electron Spins in Direct Bandgap Semiconductors for Quantum Networks

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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.