Nitrogen-vacancy (NV) color centers in diamond have emerged as a focal point in quantum technology research due to their exceptional optical and electronic spin properties. This discovery not only expands our understanding of the material properties of diamond but also paves the way for practical applications in quantum technology. As a solid-state spin quantum system characterized by long electron spin coherence times and stable performance, NV color centers offer distinct advantages in quantum information processing. Recent advancements have enabled the fabrication of high-quality NV color centers with controllable concentration and spatial positioning through techniques such as in situ doping, ion implantation, and hybrid approaches. These technological breakthroughs have significantly enhanced the efficiency of NV center fabrication, thereby establishing a robust foundation for their widespread application in quantum sensing and quantum information technologies. This review provides a comprehensive introduction to the structure and fundamental properties of NV color centers in diamond, an in-depth analysis of recent progress in their fabrication techniques, and a critical discussion of their current applications in quantum science and technology. Additionally, the challenges, open questions, and future research directions in NV color center studies are addressed.
Silicon has turned from a niche laboratory-scale material into the backbone of modern electronics. Diamond functionalized with color centers could follow a similar path and grow from proof-of-concepts experiments to application-oriented quantum technologies. Quantum sensing, communication, and information processing with color centers has been proven to work in scientific experiments and enhanced sensitivities as well as novel functionalities have been reported. While the first generation of diamond quantum devices relied on color centers formed uncontrolled in natural diamond with a high statistical variation in composition and crystallinity, the situation has changed nowadays. With the emergence of high purity monocrystals and the option for isotopic purification of the carbon matrix, technological progress in materials science on the atomic-scale enabled tailoring the spin properties in diamond. But, since many color centers typically require vacancies to combine with impurities in the carbon lattice via diffusion, the generation of color centers underlies a statistical process providing only little control on the center's final position in the crystal lattice. The negatively charged nitrogen-vacancy (NV
−) center is the most studied optically active defect in diamond and exhibits remarkable spin properties and sensing capabilities, even on the nanoscale and at room temperature. The spin properties of NV
− centers close to the surface (1\,nm - 30\,nm) have been thoroughly studied and the deeper the spins are located in diamond the less decoherence from surface defects is observed. Creating NV
− centers at the surface by nitrogen ion implantation and burying them beneath a thin diamond layer via chemical vapor deposition (CVD) of diamond is reported to enhance the coherence times significantly. By separating the color center generation from controlling the resulting depth by an additional diamond layer, narrow depth profiles can be achieved by reducing the ion energy during implantation. Although the coherence properties improve, many of the implanted NV
− center are reported to vanish in the hydrogen-rich plasma of growth CVD chambers. The mechanism responsible for the instability of NV
− centers towards the plasma remains unclear, though. One hypothesis is the formation of nitrogen-vacancy-hydrogen centers from diffusing hydrogen and implanted NV
− centers but is has not been proven, yet. Here, we demonstrate the fabrication of depth confined NV
− centers by combining low energy (1\,keV - 5\,keV) ion implantation and CVD overgrowth. By increasing the thickness of the overgrown layer (6\,nm - 100\,nm) the influence of surface noise is shown to decrease leading to bulk-like coherence properties of up to $450\,\upmu$s (Hahn-echo) and
T2∗ dephasing times around $20\,\upmu$s. Monitoring the NV
− density as a function of the overgrowth time, we analyze the kinetics of the passivation in case of implanting ion doses of 10
11 15N
+/cm
2 and 10
12 15N
+/cm
2. The passivation turns out to occur faster for lower doses offering insights into sub-surface hydrogen diffusion in diamond. Analyzing the spin bath before and after overgrowth reveals a drastic reduction in paramagnetic spins after the CVD process but no NVH
− is found around the surviving NV
− centers. Checking the chemical composition in overgrown implantation sites with secondary-ion-mass-specrometry (SIMS), however, confirms significant amounts of hydrogen in the
15N-implanted layers. Since the concentration found for hydrogen exceeds the one for nitrogen by far, we suggest that diffusing hydrogen interacts also with vacancies forming probably mostly diamagnetic defects. In the last part of this dissertation, NV
− centers are generated with sub-nanometer precision below a thin
13C-enriched layer for quantum simulation. For fabricating the spin architecture starting from a
12C base layer, we overgrow implanted nitrogen with a
13C layer and bury the spins beneath a 30\,nm-thick
12C capping layer. By measuring the coupling strength between the electron and nuclear spins, we deduce a NV
− placement accuracy reaching below one nanometer with respect to the
13C-layer. Regarding the spin properties of the electron spins, no reduction in
T2 is observed despite of the proximity to the dense
13C-bath. As a consequence, the overgrowth of NV
− centers is demonstrated as a bottom-up approach to produce buried spin architectures with sharp isotopic transitions and efficient
13C-NV
− coupling. Together with the potential for bulk-like coherence properties the synergy of implantation and overgrowth is a powerful tool to fabricate reproducible quantum systems with tailored properties and high depth confinement.
The Nitrogen-Vacancy (NV) color center is a defect of diamond which behaves as an artificial atom hosted in a solid-state matrix. Due to its electron spin properties which can be read-out and manipulated as an elementary quantum system, the NV center has found a wide panel of applications as a qubit for quantum information and as a magnetic field sensor. However these applications require to control the properties of the NV centers and their localization. This doctoral thesis investigates methods allowing us to tailor the properties of NV centers by combining techniques for the implantation of nitrogen atoms and the plasma-assisted (CVD) synthesis of diamond.The manuscript is divided into six chapters. The first chapter summarizes the properties of the NV center which will set our objectives for the NV engineering. The second chapter will describe how arrays of NV centers can be created using Focused Ion Beam implantation. The results open a wide range of applications for the targeted creation of NV centers in diamond structures such as photonic crystals and tips. However the low kinetic energy which is required for achieving implantation within a spot of 10-nm diameter leads to shallow defects which properties are strongly affected by the sample surface. The third chapter investigates how the overgrowth of a diamond layer over implanted NV centers can remove the detrimental influence of the surface. The fourth and fifth chapters describe effective methods for NV center fabrication through the control of the CVD growth conditions of the hosting crystal. Thin layers with high NV doping can be grown and almost perfect control of the orientation of the NV axis can be achieved. With the goal to optimize the spin coherence properties, the sixth chapter investigates how the electron spin of the NV center can be protected from decoherence effects induced by magnetic noise due to the unpolarized spins in the diamond lattice.
Diamond has been extensively examined as an appealing material for use in quantum optics and quantum information processing owing to the existence of various classes of optically active defects, referred to as “color centers,” which can be engineered into its crystal structure. Among these defects, the negatively charged nitrogen-vacancy center (NV−) stands out as the most prominent type. Despite the progress made, the number of emitters characterized by reproducible fabrication processes within the desired spectral range at room temperature, with limited or no damage to the parent diamond lattice, remains restricted. Herein, we are proposing for the first time the creation of the FV− center in diamond via low-energy implantation, which is particularly interesting as it possesses characteristic light absorption and magnetic properties similar to NV− centers. The low-energy ion-implanted FV centers in diamond show more desirable optical emission properties at room temperature (RT). Additionally, as per DFT calculations, the flat bands near the Fermi energy indicate dominant electron–electron interactions, an important prerequisite for observing emergent behavior as seen in systems such as twisted bi-layer graphene. Consequently, as-developed new luminescent defects such as Fluorine Vacancy Centers (FV) with desirable spectral and quantum emission properties would be a significant breakthrough in diamond-based quantum materials.
We discuss how Very Large Scale Integration (VLSI) fabrication techniques can be used to build scalable solid-state quantum computers in diamond with either room temperature operation, or low temperature operation with photonic control. For this discussion we consider nitrogen-vacancy (NV) color centers where the qubits are electron and/or nuclear spins. To achieve scalability the NV centers are placed in well-defined locations using ion implantation, and are controlled using optical and/or microwave excitation as well as localized static electric and/or magnetic fields.
Point defects in diamond, particularly nitrogen-vacancy (NV) centers, have emerged as powerful tools for a broad range of quantum technologies. These defects are promising candidates for quantum information science, serving as deterministic single-photon sources and solid-state quantum memories. They have also been employed as nanoscale quantum sensors to detect various physical quantities, including magnetic fields, electric fields, and temperature, owing to their long spin coherence time at room temperature. Development of these diamond-based quantum technologies has been rapidly boosted by a recent quantum leap in nanofabrication technologies for high-quality single-crystal diamond. Incorporating these color centers into diamond nanostructures with mature integrated photonics provides a promising route to build scalable and practical systems for quantum applications. This review discusses recent progress and challenges in the hybrid integration of diamond color centers on cutting-edge photonic platforms. Nitrogen-vacancy centers in diamond have emerged as powerful tools for a broad range of quantum technologies. This review discusses recent progress and challenges in the hybrid integration of diamond color centers on cutting-edge photonic platforms.