As a non-classical light source, single-photon source plays an essential role in the foundation of quantum physics and has been attracting a lot of attention of researchers over the world. Up to now, among different kinds of single-photon sources, single color centers in the diamond are very outstanding for the stable emission at room temperature as well as the spin controllability at ambient environment. Those color centers in the diamond with excellent properties are usually formed by impurity atoms and lattice vacancies. Nowadays, complex environments are necessary to the preparation of color centers generally. This restricts the research and applications of those color centers to a certain extent. Therefore, to develop efficient and high-precision fabrication methods of single color centers in the diamond at ambient environment is a need. On this condition, femtosecond (fs) laser process, a mature micro-nano processing technology, have been demonstrated to be a feasible, efficient, and fast production of the color centers in the diamond. This review discusses the state of the art in the preparation of single color centers in diamond and their applications in different areas.
The silicon vacancy (SiV) color centers in diamond have significant potential in the fields of quantum information, nanophotonics, bioimaging and sensing, due to its good structural stability at room temperature, strong photostability, short luminescence lifetime, narrow zero-phonon line bandwidth, and avoidance of biological autofluorescence. They have attracted extensive attention and in-depth research from researchers. The applications of SiV color centers in the above areas require addressing key issues such as control over the number and charge state of SiV color centers in diamond, as well as improving the luminous efficiency. Therefore, this review summarizes some recent relevant research progress, including common methods for preparing SiV color centers, control over their luminescence intensity, preparation of SiV single-photon sources, and research on the control of SiV color center charge states. Based on these, an outlook is provided for the preparation and application of SiV color centers in diamond.
In this paper, a brief overview of the main characteristics of lasers at NV centers in diamond is carried out. Currently, lasers at NV centers in a negative charge state generate pulsed laser radiation in the range of 714-720 nanometers with a duration of units of nanoseconds with a pulse energy of tens of microjoules and an efficiency of several percent. A significant increase in the efficiency and energy characteristics of NV lasers can be achieved through the use of multilayer reflective coatings on the faces of crystals as resonator mirrors. Lasers of this class have good prospects in the field of obtaining femtosecond pulses, since NV centers have a wide luminescence contour. Due to the high thermal conductivity of the diamond, they are able to provide generation with a high level of average power. To increase the pulse duration and transition to continuous generation, it is necessary to pump with a high level of average power. A possible solution would be injection pumping. This requires the creation of efficient light-emitting diamond electroconductive structures. In addition, the article presents new data on the study of spectral characteristics of the superluminescence of the NV centers of a diamond laser when the crystal is heated from 100 to 300 K. It is shown that the superluminescence band of such lasers actually consists of two spectral components that are not resolved at room temperature. The temperature behavior of these components is fundamentally different: the short-wave component practically does not change in intensity, while the long-wave component exponentially increases in intensity to 220 K, and then saturates and further decreases according to Mott's law. In addition, it was found that the maxima of these components experience a shift in the long-wavelength direction by about 6 meV when the temperature changes from 100 to 300 K. In the future, it is necessary to find out the exact nature and physical mechanisms of the detected phenomena, as well as to find their possible practical applications. The authors declare no conflicts of interests.
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.
Abstract Color centers, optically active defects within solids, are vital for leading quantum information technologies such as quantum computing and quantum sensing. An essential prerequisite for realizing scalable quantum architectures is the ability to create quantum emitters deterministically. In the last decades, significant efforts have been devoted to selectively generating color centers. One of the most used methods is high‐energy ion implantation. However, this method usually causes extended lattice damage along the entire trajectory because of ions bombardment. Moreover, the position depth of color centers is also limited by the ions penetrate length in crystals. The direct laser‐writing (DLW) technique has recently emerged as a powerful tool to create color centers in solid‐state materials. It can define color centers at arbitrary depths inside the substrate and operate at the ambient environment, therefore, providing a feasible 3D fabrication method for integrated quantum photonics. Here, recent advancements of laser writing of color centers in solid‐state materials are reviewed, from bulk crystals, such as diamond and silicon carbide, to nanostructures, involving single‐walled carbon nanotubes, 2D layered materials, and quantum dots.
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.