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.
We report the observation of stable optical transitions in nitrogen-vacancy (NV) centers created by ion implantation. Using a combination of high temperature annealing and subsequent surface treatment, we reproducibly create NV centers with zero-phonon lines (ZPL) exhibiting spectral diffusion that is close to the lifetime-limited optical line width. The residual spectral diffusion is further reduced by using resonant optical pumping to maintain the NV(-) charge state. This approach allows for placement of NV centers with excellent optical coherence in a well-defined device layer, which is a crucial step in the development of diamond-based devices for quantum optics, nanophotonics, and quantum information science.
Scalable realizations of quantum network technologies utilizing the nitrogen vacancy center in diamond require creation of optically coherent NV centers in close proximity to a surface for coupling to optical structures. We create single NV centers by
15N ion implantation and high-temperature vacuum annealing. Origin of the NV centers is established by optically detected magnetic resonance spectroscopy for nitrogen isotope identification. Near lifetime-limited optical linewidths (
< 60 MHz) are observed for the majority of the normal-implant (7
∘,
≈ 100 nm deep)
15NV centers. Long-term stability of the NV
− charge state and emission frequency is demonstrated. The effect of NV-surface interaction is investigated by varying the implantation angle for a fixed ion-energy, and thus lattice damage profile. In contrast to the normal implant condition, NVs from an oblique-implant (85
∘,
≈ 20 nm deep) exhibit substantially reduced optical coherence. Our results imply that the surface is a larger source of perturbation than implantation damage for shallow implanted NVs. This work supports the viability of ion implantation for formation of optically stable NV centers. However, careful surface preparation will be necessary for scalable defect engineering.
We characterize single nitrogen-vacancy (NV) centers created by 10-keVN+ ion implantation into diamond via thin SiO2 layers working as screening masks. Despite the relatively high acceleration energy compared with standard ones (<5keV) used to create near-surface NV centers, the screening masks modify the distribution of N+ ions to be peaked at the diamond surface [Ito et al., Appl. Phys. Lett. 110, 213105 (2017)]. We examine the relation between coherence times of the NV electronic spins and their depths, demonstrating that a large portion of NV centers are located within 10 nm from the surface, consistent with Monte Carlo simulations. The effect of the surface on the NV spin coherence time is evaluated through noise spectroscopy, surface topography, and x-ray photoelectron spectroscopy.
The nitrogen-vacancy (NV) center in diamond is a promising candidate for development of quantum communication and simulation devices which are based on the control of coupled quantum systems. It offers an optical readout of its spin state, exhibits long coherence times and allows to coherently control nearby nuclear spins, e.g. from 13C nuclei, even at room-temperature. For successful demonstration of such systems however, controlling the nuclear spin environment, and thus tuning the coupling strengths is crucial to allow the fabrication of a scalable platforms. The combination of Chemical Vapor Deposition (CVD) of diamond as a method with isotopic control on the diamond composition and ion implantation as a tool to reliably create NV centers is a perfect toolkit to study the realization such quantum systems.
Scalable realizations of quantum network technologies utilizing the nitrogen-vacancy (NV) center in diamond require creation of optically coherent NV centers in close proximity to a surface for coupling to optical structures. We create single NV centers by
15N ion implantation and high-temperature vacuum annealing. The origin of the NV centers is established by optically detected magnetic resonance spectroscopy for nitrogen isotope identification. Near-lifetime-limited optical linewidths
(<60MHz) are observed for the majority of the normal-implant (${7}^{\ensuremath{\circ}}$, $\ensuremath{\approx}100$ nm deep)
15NV centers. Long-term stability of the ${\mathrm{NV}}^{\ensuremath{-}}$ charge state and emission frequency is demonstrated. The effect of NV-surface interaction is investigated by varying the implantation angle for a fixed ion energy, and thus lattice damage profile. In contrast to the normal-implant condition, NVs from an oblique implant (${85}^{\ensuremath{\circ}}$, $\ensuremath{\approx}20$ nm deep) exhibit substantially reduced optical coherence. Our results imply that the surface is a larger source of perturbation than implantation damage for shallow implanted NVs. This work supports the viability of ion implantation for formation of optically stable NV centers. However, careful surface preparation will be necessary for scalable defect engineering.