Towards Engineering Point Defects for Quantum Information

Abstract

Point defects in nonmetallic solids have recently been proposed as promising platforms for quantum information technologies. In creating isolated electronic states separated from the bulk bands of the solid, these defects can effectively behave as ``artificial atoms.'' These systems can ideally be manipulated to produce coherent spins and/or coherent single photons, both of which are useful for quantum applications, and can do so at reasonable temperatures. The properties of these defects, and their corresponding utility in these applications, depends on many factors, including most importantly their electronic structure. In this thesis, we discuss our theoretical work towards engineering point defects with desired electronic and optical properties. The first half of this thesis explores defect electronic structure and spin dynamics for novel defect centers in diamond. We investigate the previously-unexplored group III centers and find they have desirable optical and spin properties for realistic doping levels. We also investigate the nuanced interplay between Jahn-Teller distortions and spin-orbit coupling of group IV0 defects. Ultimately we show that the large product Jahn-Teller effect present in the excited state of these systems causes a strong quenching of spin-orbit interactions. These combined effects are found to have important implications on the fine level structure of the corresponding defects. We also discuss our work on predicting the defect spin dynamics, including population and coherence. We propose an extension to the cluster-correlation expansion (CCE) technique which is able to capture the effects of nuclear spin interactions on the central defect spin, as well as coupling to an additional nearby defect spin. The first half reveals the importance of accurate calculations and understanding of interactions present in these defect systems to ultimately capture the relevant properties of interest. In the second half, we focus on the promise of emerging 2D materials as hosts for defect systems. These materials provide a particularly realistic platform for which rational design of defect systems may be realized. We discuss our work on capturing unique interactions related to 2D systems in particular, such as spin-selective electronic transitions, interactions with substrates, and the importance of strain and disorder on the atomic scale. Finally we discuss our work on defects in 2D systems. We investigate the role of spin-orbit coupling in vacancy defects in transition metal dichalcogenides MoS2 and WS2. We also propose the idea of nearby defects in 2D flakes of hexagonal Boron Nitride as ``artificial molecules.'' To end, we give an outlook on the potential for this work and this field going forward.