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.
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.
Defects with associated electron and nuclear spins in solid-state materials have a long history relevant to quantum information science going back to the first spin echo experiments with silicon dopants in the 1950s. Since the turn of the century, the field has rapidly spread to a vast array of defects and host crystals applicable to quantum communication, sensing, and computing. From simple spin resonance to long-distance remote entanglement, the complexity of working with spin defects is fast advancing, and requires an in-depth understanding of their spin, optical, charge, and material properties in this modern context. This is especially critical for discovering new relevant systems dedicated to specific quantum applications. In this review, we therefore expand upon all the key components with an emphasis on the properties of defects and the host material, on engineering opportunities and other pathways for improvement. Finally, this review aims to be as defect and material agnostic as possible, with some emphasis on optical emitters, providing a broad guideline for the field of solid-state spin defects for quantum information.
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.
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.
Thin films with quantum defects are emerging as a potential platform for quantum applications. Quantum defects in some thin films arise due to structural imperfections, such as vacancies or impurities. These defects generate localized electronic states with unique optical and electronic properties. Crystal vacancies or defects that occur when atoms are missing from a crystal lattice can influence a material's quantum properties. In this study, we investigated inexpensive, complementary metal oxide semiconductor compatible materials with quantum defects suitable for room temperature applications. The experiments indicated 5, 15, and 17 ns relaxation times for aluminum nitride, aluminum oxide or alumina, and tin oxides, respectively. For all these materials, distinct resonant peaks are observed at approximately 1.1, 1.6, 2.2, and 2.7 GHz at room temperature (i.e., 21 °C). These peaks exhibit slight frequency shifts, corresponding to known defect locations and thin film material properties. This discovery may lead the way to reliable, cost-effective quantum applications in our daily lives.
Quantum information science is entering a second phase, the Quantum Evolution 2.0, in which the challenge has shifted from demonstrating coherent control of individual quantum states to building scalable multi-qubit processors and networks. This transition places materials science at the center of the field. Across superconducting circuits, quantum defects, quantum photonic devices, and emerging materials platforms, including two-dimensional materials and heterostructures, performance is now limited less by device design than by poorly controlled surfaces, buried interfaces, and defects whose atomic identities remain incompletely known. This review surveys the materials challenges of these quantum platforms together with the characterization methods needed to resolve them. For each platform we identify the dominant decoherence mechanisms, the current state of materials understanding, and the most pressing open materials problems. A cross-platform comparison then reveals a shared structure-coherence problem. The implicated material chemistry recurs across platforms, involving light elements in disordered or buried environments, yet no platform can quantitatively connect a specific atomic-scale structure to a measured change in coherence. We close by identifying three needs, mechanistic understanding of decoherence at the atomistic level, high-throughput proxy metrics predictive of device performance, and characterization tools built for quantum materials, whose resolution would advance coherence, scalability, and integration across all platforms.
ABSTRACT Quantum computing leverages the principles of quantum mechanics to perform computations that are infeasible for classical computers. Color centers, which are point defects in a crystal lattice where vacancies in the lattice and/or an impurity atom replace a host atom, exhibit unique optical, electronic, and nuclear spin properties that make them suitable for quantum information and communication processing as well as for quantum computations with quantum memory. Among the color centers, nitrogen‐vacancy centers in diamond, the most developed, silicon vacancy (V Si ) centers in silicon carbide (SiC), and boron vacancy (V B ) centers in hexagonal boron nitride (hBN) have emerged as leading candidates. Diamond and SiC material hosts are particularly promising due to the long spin and photon coherence times, optical addressability, compatibility with various quantum operations, while SiC promises higher compatibility with scalable industrial fabrication processing, and 2D materials are better suited for hybrid photonics and electronics integration. This paper provides a detailed overview of the advantages, challenges, and recent advancements in using these color centers for quantum computing. In addition, it discusses other potential color centers of interest, such as silicon (SiV) and germanium (GeV) vacancies in diamond, tin vacancies (SnV) in diamond, chromium and nickel centers in diamond, and rare‐earth ions in host materials like yttrium orthosilicate and calcium fluoride. By understanding and utilizing the properties of these diverse color centers, researchers aim to develop more efficient, scalable, and versatile quantum computers, which could lead to hybrid quantum‐classical systems that combine the strengths of different platforms and potentially transform fields like cryptography, material science, drug discovery, and complex system simulations (climate modeling, fusion energy).