Engineering Dipolar Interactions in Wide Bandgap Semiconductors Using Donor-Acceptor Pairs

The control of dipolar interactions between quantum emitters in solid-state hosts is a central challenge for the development of scalable quantum information platforms and quantum-enabled devices. While atomic systems - such as trapped ions and Rydberg atoms - have long demonstrated tunable, long-range dipole coupling suitable for quantum logic, extending these concepts into the solid state requires identifying defect systems that combine strong intrinsic dipole moments with robust optical addressability and compatibility with nanophotonic architectures. This thesis presents a series of first-principles investigations of donor-acceptor pairs (DAPs) and surface-defect pairs (SDPs) in wide-bandgap semiconductors, primarily focusing on diamond and silicon carbide (SiC), as candidate hosts for achieving coherent dipole-based coupling in scalable solid-state environments. Through systematic density functional theory (DFT) calculations, including constrained excited state simulations, phonon coupling analysis, and electric field response modeling, the thesis establish both the opportunities and the limitations of various defect architectures for realizing optically controllable dipolar networks. In the first part of this work, I explore DAPs in bulk diamond and 3C-SiC, focusing on their electronic structure, charge transition levels, zero-phonon line (ZPL) energies, and their resulting photoluminescence spectra. The calculations reveal that certain substitutional donor-acceptor pairs exhibit large electric dipole moments - exceeding those of conventional point defects by orders of magnitude - and support narrow optical transitions with high Debye-Waller factors. Importantly, I demonstrate that the strength of dipolar coupling between DAPs can be systematically tuned by addressing donor-acceptor pairs with varying interatomic separation. These results establish a route toward engineering arrays of DAPs with interaction strengths suitable for implementing non-photonic two-qubit gates. However, this initial study also highlights key limitations: in the bulk, the orientation of DAP dipoles is random due to the lack of controlled positioning, and the dipoles are "on" in the ground state, and "off" in the excited state, which is opposite to conventional trapped atom Rydberg systems and complicates their control. Motivated by these challenges, the second part of this thesis extends the DAP framework to surfaces. Using ab initio calculations, I investigate the properties of DAPs and SDPs near hydrogen-terminated and hydroxyl-terminated SiC surfaces. I show that surface terminations can be exploited to engineer the electrostatic environment of near-surface defects, stabilizing configurations with highly aligned dipole moments. Unlike in the bulk, SDPs exhibit well-defined dipole orientations perpendicular to the surface plane, enabling deterministic control over coupling strengths and allowing for integration into planar photonic structures. I further compute polarization-resolved stimulated emission and photoionization cross sections for these systems, demonstrating that optical transitions can be selectively enhanced or suppressed via the polarization of incident light. The final part of this thesis focuses on the field-induced response of the negatively charged germanium-vacancy (GeV) center, which belongs to the emerging class of Group IV-vacancy centers in diamond. This is a collaborative effort where I develop a second-order Stark shift model of the GeV's ZPL based on constrained DFT calculations, extracting the full polarizability tensor and constructing polar maps of spectral sensitivity to nearby fluctuating charges. This work resolves long-standing experimental observations of unexplained spectral jumps in GeV emission lines, demonstrating that the observed behavior can be fully accounted for by second-order Stark shifts induced by local charge fluctuations in the defect's environment. These insights also provide a predictive framework for mitigating spectral instability in GeV-based quantum devices. Taking all these results together, this thesis advances the fundamental understanding of dipolar defect physics in wide-bandgap semiconductors and provides a roadmap for engineering optically controllable, dipole-coupled defect systems. The results demonstrate that while bulk DAPs provide a rich playground for exploring dipolar interactions, their practical deployment will likely require surface-based architectures or hybrid schemes to overcome limitations of orientation randomness and dipole inversion. The surface-defect pairs developed here offer a concrete path towards integrating defect-based qubits into scalable, tunable quantum photonic platforms by building two-dimensional arrays of such systems and interfacing them with other nanophotonic control devices.