Shallow Donor Qubits in ZnO Nanowires for Quantum Applications

Abstract

Donors in ZnO are a promising candidate for quantum network-based quantum technologieswith narrow optical lines (7-20 GHz), efficient spin-to-photon transfer (∼90% zero-phonon line efficiency), and long spin coherence times (50 µs Hahn spin-echo T2) demonstrated in ensembles in bulk [58]. Two outstanding challenges for this system include the isolation of single donor defects and the incorporation of these donors into nanostructures. In this thesis, we utilize ZnO nanowires to address these challenges. We begin by testing several methods of single nanowire isolation, including scanning optical microscopy of ZnO/GaN samples, ion beam milling, exfoliation, and dropcasting. After identifying the most promising methods, favorable optical and spin properties are confirmed to be retained in single ZnO nanowires. Photoluminescence excitation spectroscopy confirms narrow linewidths, optical pumping demonstrates spin initialization, and coherent population trapping is used to prepare a coherent spin state. Finally, two non-standard growth recipes are used to try to address the strain caused by the current method of single nanowire isolation and the large observed surface exciton. In conclusion, by isolating small ensembles of donors using nanowires and showing that these donors can be incorporated into nanostructures, this thesis shows that shallow donors in ZnO have great promise toward use in future quantum technologies.