Physics PhD Thesis Defense: “Characterization of Solid State Defect Systems For Quantum Computing, Communication, and Sensing”

Solid state defects have emerged as a leading candidate for platforms in quantum computing, communication, and sensing. The electronic spins localized around these defects have many advantages such as room temperature coherence, spin dependent optical transitions which enable visible-wavelength initialization and readout, and resonant frequencies compatible with widely available off-the-shelf microwave hardware. Furthermore, the nuclear spins coupled to these electronic spins provide additional quantum registers which can be used as long-lived memories, ancilla qubits to enhance sensing and communication schemes based on the electronic spin, or for general purpose computation. However, unlike systems which are all identical, such as trapped atoms, or systems which are man-made, such as superconducting circuits, the formation and structure of defects, as well as their coupled nuclear spins, is stochastic and difficult to model using \textit{ab initio} methods. This thesis focuses on methods to efficiently and precisely characterize the properties of these systems. After presenting sufficient background for a general scientific audience, a method is outlined for robustly and efficiently quantifying the optical properties of defect-based emitters, even if the emitters are heterogeneous. We show how this method can be used to study treatment effects in novel systems, such as hexagonal Boron Nitride (hBN), where a new class of defect-based emitters has been identified but proven difficult to characterize – largely due to the widely varying optical properties of emitters which are believed to arise from the same defect. We then describe the infrastructure developed within the laboratory to generate, run, and simulate the results of experiments such as those used in the remainder of the thesis. This is followed by an explanation of some of the state of the art techniques used to identify, control, and map the nuclear spins coupled to an electronic spin within a defect system. We then show how these techniques can be expanded to precisely measure the Hamiltonian parameters of a single nuclear spin – which opens the door to a new era where individual nuclear spins can be used to measure their environment and reveal information about the local molecular and crystal structure. Finally, this thesis concludes with a brief discussion of the ongoing work and future directions inspired by the ideas and work presented in this thesis.