Nitrogen-vacancy (NV) centers in diamond are gaining attention as room-temperature quantum bits, with potential applications in quantum sensing, quantum information processing, and quantum communication. Precise positioning of NV centers is crucial for creating efficient single-photon sources using optical resonators and quantum memories for quantum interface, etc. Generally, broad ion beam implantation through nanohole fabricated by electron beam lithography has been widely used for precise creation of NV centers. There are several reports of deterministic NV creation by using pulsed fs- or ps-laser irradiations. In addition, focusing ion beam implantation provides a route towards scalable quantum information processing [3-6]. In this study, we are developing an inherently deterministic single-ion implantation method based on a linear Paul trap (LPT) as a single-ion source, since the laser-cooling technique can be applied to the trap system to obtain ultralow-emittance ions and manipulate single ions one by one. The QST system uses doubly charged ions cooled with calcium ions, allowing 100 keV ion implantation in diamond.
Deterministic ion implantation and color-center creation methods at the nanometer scale provide a route towards scalable quantum information processing. For this purpose, we have developed an inherently deterministic single-ion implantation method based on a linear Paul trap (LPT) as a single-ion source since the laser-cooling technique can be applied to the trap system to obtain ultralow-emittance ions and manipulate single ions one by one . Doubly charged nitrogen ions (N2+) produced in a sputter ion source is introduced into the LPT and sympathetically cooled with laser-cooled calcium ions (Ca+). Both the sputter ion source and the LPT chamber are elevated to +50kV for the 100keV-implantation of doubly charged single ions into a grounded diamond crystal.
Abstract Scalable quantum computing and communication systems strictly require the development of highly integrated quantum hardware. While prominent implementations like superconducting and semiconductor spin qubits show integration progress, their reliance on extreme cryogenic conditions raises substantial sustainability concerns, especially given global helium depletion. In contrast, solid-state quantum devices, such as nitrogen-vacancy (NV) centers, offer room-temperature operation. Although ensemble solid-state defects have been successfully utilized in quantum sensing, the realization of complex quantum registers requires highly precise arrays of single, coupled qubits. Currently, their practical integration into scalable multi-qubit arrays is fundamentally limited by the technical challenge of achieving deterministic, ultra-precise atomic injection at the angstrom scale. This Perspective examines the current state of solid-state quantum system integration, identifying recent advances and persistent bottlenecks, particularly focusing on the limitations of cooling ion sources based on Paul traps. We then propose a novel architecture combining established neutral-particle decelerator techniques with deterministic ionization to overcome these fundamental operational hurdles. This analysis aims to present a viable path for advanced integrated solid-state quantum platform development, fostering broader adoption and sustainable evolution.
Split-vacancy color centers in diamonds are promising solid-state platforms for the implementation of photonic quantum technologies. These luminescent defects are commonly fabricated upon low-energy ion implantation and subsequent thermal annealing. Their technological uptake will require the availability of reliable methods for the controlled, large-scale production of localized individual photon emitters. This task is partially achieved by controlled ion implantation to introduce selected impurities in the host material and requires the development of challenging beam focusing or collimation procedures coupled with single-ion detection techniques. We report on the protocol for the direct optical activation of split-vacancy color centers in diamond via localized processing with a continuous-wave laser at mW optical powers. We demonstrate the activation of photoluminescent Mg- and Sn-related centers at both the ensemble and single-photon emitter levels in ion-implanted, high-purity diamond crystals without further thermal processing. The proposed lithographic method enables the activation of individual color centers at specific positions of a large-area sample by means of a relatively inexpensive equipment offering real-time, in situ monitoring of the process.
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.