Editorial: Advanced material design and post-treatment techniques for enhancing color centers in quantum technologies

Introduction

Color centers in wide-bandgap materials have emerged as one of the most promising platforms for quantum technologies, offering atomic-scale quantum systems that can serve as qubits, single-photon sources, and nanoscale sensors. Point defects consisting of either impurity atoms paired with vacancies or isolated vacancies in a crystal lattice can be optically initialized, coherently manipulated, and read out, in many cases even at room temperature. Their atomic scale and remarkable quantum properties have spurred intense research efforts aimed at harnessing color centers for quantum sensing, quantum communication, and quantum information processing.

The motivation behind this Research Topic was to compile and critically evaluate innovative methods for the fabrication of color centers tailored to quantum technologies. A particular emphasis was placed on approaches where defects are created or optimized during material synthesis, as well as on post-growth treatments that optimize color center properties without requiring additional implantation of an impurity atom. The Research Topic was deliberately designed to encompass a broad range of host materials—from established platforms such as diamond and silicon carbide (SiC) to emerging two-dimensional materials like hexagonal boron nitride (hBN).

This Research Topic is timely for several reasons. While the fundamental physics of many color centers is increasingly well understood, the translation of laboratory demonstrations into scalable, reproducible quantum devices remains a major challenge. Achieving this requires advances across the full materials processing chain: from substrate preparation and crystal growth, through defect creation and activation, to surface engineering and charge-state stabilization. Even minute changes to process conditions can result in drastic changes in defect properties. The articles assembled here address these challenges from complementary angles, providing both broad perspective and targeted experimental advances.

It is notable that all contributions to this Research Topic focus on diamond as the host material, and specifically on the nitrogen-vacancy (NV) center. This outcome, while not by design, reflects the current maturity of the field. Diamond remains the most extensively studied and technologically advanced platform for color-center-based quantum technologies, with decades of accumulated knowledge on growth, processing, and defect engineering. Silicon carbide, although it hosts a rich variety of color centers (such as the silicon vacancy and divacancy) with attractive properties including near-infrared emission and CMOS-compatible fabrication, has seen comparatively fewer systematic studies on growth-based defect engineering and post-treatment optimization at the level represented here. This may be related to SiC epitaxy being conducted predominantly at an industrial scale rather than in an academic setting, where process stability is paramount and deliberate variations introduced to improve color center properties risk compromising that stability.

Hexagonal boron nitride, a newer entrant to the field, offers bright single-photon emitters at room temperature and intriguing possibilities for integration with van der Waals heterostructures; however, the identification of specific defect species and their precise properties remains an active area of investigation. The relative immaturity of fabrication control in this emerging material may explain the absence of hBN contributions from this Research Topic and underscores the continued need for dedicated research efforts in both this host material and SiC.

The five articles published under this Research Topic can be organized around three interconnected themes: (i) materials synthesis and growth optimization, (ii) post-growth and post-treatment strategies for defect activation and property enhancement, and (iii) deterministic defect placement and orientation control. Together, they span the processing pipeline from bulk crystal engineering to single-defect manipulation.

Comprehensive process review

The review by Hammock et al. provides a practice-oriented synopsis of diamond processing for quantum-grade NV and group-IV vacancy (G4V) centers. Organized around the fabrication lifecycle—substrate preparation, chemical vapor deposition (CVD) growth, post-synthesis activation, and band engineering for charge stabilization—this article synthesizes experimental studies, first-principles theory, and hands-on process knowledge into an actionable guide. The review highlights critical but often underappreciated steps such as subsurface damage removal, in situ thermal degassing to mitigate hydrogen passivation of NV centers, and the competing defect pathways (vacancy clustering, interstitial recombination) that limit activation yields. By collecting best practices and identifying key metrology gaps, this contribution lowers the barrier for new groups entering the field and establishes practical benchmarks for reproducibility.

Growth optimization for pulsed magnetometry

Tang et al. report the synthesis and characterization of low-nitrogen-concentration (∼0.8 ppm) diamond material engineered for pulsed NV ensemble magnetometry. By combining low-strain CVD growth on carefully selected substrates, ¹²C isotopic purification, and controlled electron irradiation and annealing, the authors achieve spin-bath-limited NV dephasing times of ∼17.5 µs—close to the theoretical limit for this nitrogen concentration. Through systematic comparison with higher-nitrogen (∼14 ppm) diamond across a wide range of optical excitation intensities, they demonstrate that low-nitrogen material can offer superior photon-shot-noise-limited DC magnetic field sensitivity, particularly at moderate and low optical powers. This finding has practical implications for applications with constrained size, weight, power, and cost, as well as for biological sensing where phototoxicity from intense laser illumination must be minimized.

Systematic annealing of diamond microparticles

Nunn et al. present a systematic study of low-pressure high-temperature (LPHT) annealing of ∼3 µm fluorescent diamond particles across temperatures from 1200 °C to 1800 °C and durations of 5–30 min. They demonstrate that annealing in the range of 1400 °C–1700 °C markedly improves NV spin properties: ODMR contrast increases from ∼9% to ∼13%, the zero-field splitting strain parameter E decreases significantly, and T₁ relaxation times approach ∼5 ms—values typical of bulk diamond. Quantitative electron paramagnetic resonance (EPR) measurements allow the authors to estimate activation energies for P1 center aggregation (3.63 eV) and NV center annihilation (3.89 eV), providing mechanistic insight into the defect dynamics governing these improvements. The practical impact is demonstrated through a roughly two-fold reduction in the noise level of NV-based temperature measurements using optimally annealed particles.

Post-treatment of fluorescent nanodiamonds

Alkahtani et al. address the challenge of producing quantum-grade fluorescent nanodiamonds (FNDs) through a multistep surface treatment protocol combining molten potassium nitrate (KNO₃) etching with sequential acid and alkaline cleaning. This integrated approach yields nanodiamonds with enhanced photoluminescence, high ODMR contrast (∼11.5%), extended spin-lattice relaxation times (T₁ ∼ 2 ms), and excellent colloidal. The study highlights that comprehensive surface engineering—addressing graphitic residues, ionic contamination, and charge instability simultaneously—is essential for realizing the full quantum sensing potential of nanodiamond platforms, particularly for biological and fluid-phase applications.

Deterministic orientation control of single NV centers

Klink et al. introduce an all-optical method for reorienting individual laser-written NV centers along a desired crystallographic axis using femtosecond laser annealing. By combining ultrafast laser writing for spatial placement with in situ polarization analysis and repeated annealing cycles, the authors demonstrate deterministic alignment of NV centers along the optical axis in (111)-oriented diamond and selection between two distinguishable orientation classes in (100)-oriented substrates. A 3 × 3 array of uniformly oriented NV centers is produced, showcasing the scalability of the approach. This capability addresses a long-standing limitation of laser-written NV centers—their random orientation—which reduces measurement contrast and sensitivity in magnetometry applications.

Advancing the field

Taken together, these contributions advance research on color centers in quantum technologies along several fronts. First, they demonstrate that the full processing chain—from substrate selection and growth parameter optimization to post-growth annealing and surface treatment—must be considered holistically; improvements at any single step can be undermined by deficiencies elsewhere. Second, they provide quantitative benchmarks (dephasing times, ODMR contrast, activation energies, sensitivity estimates) that enable direct comparison between different material grades, processing routes, and application scenarios. Third, they illustrate that both bulk single-crystal diamond and particulate/nanodiamond formats can benefit substantially from optimized thermal treatments, reinforcing the importance of understanding defect kinetics and competitive pathways at a fundamental level. Finally, the demonstration of deterministic spatial and orientational control of single NV centers opens new avenues for scalable quantum device architectures that were previously inaccessible.

We hope that this Research Topic serves as both a practical resource and a stimulus for further research on the fabrication and optimization of color centers across the full range of wide-bandgap host materials for quantum technologies, and that it helps accelerate their translation into practical industrial applications.