Identifying scalable materials systems that exhibit quantum behavior is a central challenge in quantum information science. Point defects in certain wide-bandgap semiconductors are promising in this regard due to the maturity of semiconductor manufacturing and ion implantation technology. Single erbium defect centers in 4H-SiC are examples of such defects that provide access to discrete defect-induced electron energy levels within the bulk material bandgap, which can be utilized for a variety of quantum technologies, such as single-photon emission for secure communication and distributed quantum computing. This work presents a first-principles study of erbium point defects in 4H-SiC using density functional theory. These results provide materials-level support for the development of Er point defects in 4H-SiC as a scalable platform for quantum devices, helping to bridge the gap between quantum physics and the practical realization of quantum networks.
Identifying scalable materials systems that exhibit quantum behavior is a central challenge in quantum information science. Point defects in certain wide-bandgap semiconductors are promising in this regard due to the maturity of semiconductor manufacturing and ion implantation technology. Single erbium defect centers in 4H-SiC are examples of such defects that provide access to discrete defect-induced electron energy levels within the bulk material bandgap, which can be utilized for a variety of quantum technologies, such as single-photon emission for secure communication and distributed quantum computing. This work presents a first-principles study of erbium point defects in 4H-SiC using density functional theory. These results provide materials-level support for the development of Er point defects in 4H-SiC as a scalable platform for quantum devices, helping to bridge the gap between quantum physics and the practical realization of quantum networks.
Quantum photonics is an emerging field of photonics where single photons are used for applications in quantum computation, quantum communication, and quantum sensing. One of the key enablers of these new technologies is colour centres. Colour centres are isolated defects in crystals that are able to emit single photons and have spin properties that can be exploited for quantum technologies. These properties include high brightness, low photo-bleaching, and room-temperature optically accessible spins. Wide-bandgap semiconductors such as diamond, silicon carbide and gallium nitride, and 2D materials such as h-BN and TMDs are of particular interest as host materials for colour centres. Numerous light emitters have been discovered and documented in these materials. Colour centres typically occur naturally in semiconductors and are often introduced during the growth process. This random distribution of defects is clearly not desirable for making quantum devices as it makes it difficult to process the materials and introduce structures that interact with these defects such as electrical contacts. The key technology that allows for the precise engineering of colour centres and other quantum defects in materials is ion implantation. Ion implantation utilizes energetic ion beams for the modification of electrical, optical, and magnetic properties of materials. It is a key processing step that has been widely used in the semiconductor industry for doping of semiconductors and for creating buried oxides. Ion implanters that are currently used in industry are designed for uniform wafer-level implantation of relatively large fluences of ions with high beam currents. The new quantum technologies, such as quantum computing, require a major paradigm shift in the way in which ion implantation is performed.
This thesis describes studies on atomic point defects in semiconductors for applications in quantum information. In particular, its focus is on defects whose energy levels reside deep within the bandgap certain semiconductors because these systems can behave like artificial trapped atoms in the solid state, possessing optical addressability, long coherence times, and the ability to be manipulated at microwave frequencies. The most prominent defect in this field of study is the diamond nitrogen-vacancy center, whose functionality is well-known to persist to ambient temperature. The first part of this thesis investigates the persistence of this functionality to temperatures upwards of 600 K. Importantly, these investigations also demonstrate that the diamond nitrogen-vacancy center can be a sensitive thermometer (~10 mK/Hz^(1/2)) over a wide range of temperatures with nanoscale spatial resolution. The latter part of the thesis describes experimental measurements of divacancy defects in silicon carbide, a potential alternative materials host to diamond with established wafer-scale growth and microfabrication capabilities. Single divacancy spins are isolated and coherently controlled for the first time in the 4H polytype of silicon carbide, and the divacancy's coherence is shown to be a remarkably long T2 = 1.2 ms at T = 20 K. The last chapter extends these results by isolating single divacancies in the 3C polytype, experimentally demonstrating a qualitative and quantitative model of their spin and orbital dynamics, and revealing the divacancy's excited state level structure in both the 3C and 4H polytypes using resonant laser techniques. These excited state transitions are shown to posses a structure identical to the diamond nitrogen-vacancy center and a subset are shown to have favorable cycling properties. The location of a clear spin-photon interface has important implications for high-fidelity quantum state readout and photon-based entanglement schemes that use divacancy spins.
Quantum networks based on solid-state spin defects present a transformative approach to secure communication and distributed quantum computing, utilizing quantum entanglement and coherent spin–photon interfaces. Silicon carbide (SiC) stands out as a compelling material platform due to its unique combination of a wide bandgap, high optical nonlinearity, CMOS-compatible fabrication, and controllable spin-active defects. These intrinsic properties facilitate efficient photon emission, robust spin coherence at both room and cryogenic temperatures, and integration with photonic nanostructures. Recent advancements in defect engineering and micro-nanophotonics have unlocked the potential of SiC quantum nodes, which feature electron-nuclear spin systems for high-fidelity quantum operations and long-lived quantum memories. Key steps such as single-shot readout and spin-photon entanglement have been successfully demonstrated, bringing SiC closer to a real quantum network platform. This review offers a comprehensive overview of the advancements in SiC-based quantum networks, encompassing key aspects such as defect fabrication methodologies, optimization of spin-photon interfaces, and strategies for photonic integration. Additionally, it examines the existing challenges and outlines promising future directions in this rapidly evolving field.
Abstract Optically active point defects in wide‐bandgap crystals are leading building blocks for quantum information technologies including quantum processors, repeaters, simulators, and sensors. Although defects and impurities are ubiquitous in all materials, select defect configurations in certain materials harbor coherent electronic and nuclear quantum states that can be optically and electronically addressed in solid‐state devices, in some cases even at room temperature. Historically, the study of quantum point defects has been limited to a relatively small set of host materials and defect systems. In this article, we consider the potential for identifying defects in new materials, either to advance known applications in quantum science or to enable entirely new capabilities. We propose that, in principle, it should be possible to reverse the historical approach, which is partially based on accidental discovery, in order to design quantum defects with desired properties suitable for specific applications. We discuss the biggest obstacles on the road towards this goal, in particular those related to theoretical prediction, materials growth and processing, and experimental characterization.
Silicon carbide (SiC) has become a key player in the realization of scalable quantum technologies due to its ability to host optically addressable spin qubits and wafer-size samples. Here, we have demonstrated optically detected magnetic resonance (ODMR) with resonant excitation and clearly identified the ground state energy levels of the NV centers in 4H-SiC. Coherent manipulation of NV centers in SiC has been achieved with Rabi and Ramsey oscillations. Finally, we show the successful generation and characterization of single nitrogen vacancy (NV) center in SiC employing ion implantation. Our results highligh the key role of NV centers in SiC as a potential candidate for quantum information processing.