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Highly coherent nitrogen-vacancy centres in diamond via rational high-pressure and high-temperature synthesis and treatment

Xiaoran Zhang, Kang-yuan Liu, Fengjiao Li, Xiaobing Liu, Shuai Duan, Jianing Wang, Gang‐Qin Liu, Xinyu Pan, Xin Chen, Ping Zhang, Yanming Ma, Changfeng Chen

Published Oct 10, 2022• 0 citations
Publisher

Abstract

Abstract Nitrogen-vacancy (NV-) centres in diamond offer an excellent platform for device design and development in the emerging fields of quantum sensing and quantum network, but fabrication of quantum-grade diamonds with highly coherent NV- centres needed for advanced applications presents a pressing challenge. Here we report a major advance in generating NV- centres in diamonds via tailored high-pressure and high-temperature (HPHT) synthesis and post-grown annealing treatment. The resulting well dispersed single NV- centres in type-IIa diamonds exhibit long spin coherence times reaching the highest levels achieved in diamonds prepared by more elaborate and restrictive chemical vapor deposition techniques. Moreover, we produce high-density NV- ensembles in <100>-grown type-Ib diamonds with superb zero-phonon lines considerably sharper than those of native NV- centres in as-grown diamonds. These findings demonstrate a superior synthesis and optimization protocol for creating top-quality NV- centres to meet the most stringent requirements for a wide range of emerging quantum technologies.

DOI
10.21203/rs.3.rs-2102428/v1

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Abstract Nitrogen-vacancy (NV-) centres in diamond offer an excellent platform for device design and development in the emerging fields of quantum sensing and quantum network, but fabrication of quantum-grade diamonds with highly coherent NV- centres needed for advanced applications presents a pressing challenge. Here we report a major advance in generating NV- centres in diamonds via tailored high-pressure and high-temperature (HPHT) synthesis and post-grown annealing treatment. The resulting well dispersed single NV- centres in type-IIa diamonds exhibit long spin coherence times reaching the highest levels achieved in diamonds prepared by more elaborate and restrictive chemical vapor deposition techniques. Moreover, we produce high-density NV- ensembles in <100>-grown type-Ib diamonds with superb zero-phonon lines considerably sharper than those of native NV- centres in as-grown diamonds. These findings demonstrate a superior synthesis and optimization protocol for creating top-quality NV- centres to meet the most stringent requirements for a wide range of emerging quantum technologies.
Abstract The high‐pressure and high‐temperature (HPHT) diamonds with well‐controlled defects and low stress offer an ideal host substrate for the fields of quantum information science; however, fabrication of quantum‐grade HPHT diamonds remains a pressing challenge. Here, a major advance in generating highly coherent nitrogen‐vacancy (NV) centers, a promising spin defect in diamonds, via tailored HPHT synthesis and postgrown annealing treatment is reported. The resulting well‐dispersed single NV− centers in type‐IIa diamonds exhibit long spin coherence times comparable to that of the reported chemical vapor deposition diamonds. Moreover, high‐density NV− ensembles in 〈100〉‐grown type‐Ib diamonds with superb zero‐phonon lines considerably sharper than those of native NV− centers in as‐grown diamonds, together with low splitting of resonances are produced. These findings demonstrate a superior synthesis and optimization protocol for creating high‐quality NV− centers avoiding lattice damage in diamond to meet the stringent requirements for a wide range of emerging quantum technologies.
ABSTRACT With unique optical and spin properties, the negatively charged nitrogen‐vacancy (NV − ) center in diamond has become a leading physical platform for quantum information processing. Fabrication of NV centers involves three steps: introducing nitrogen atoms, creating lattice vacancies, and combining these two types of defects. The final step is typically achieved by high‐temperature annealing, as vacancy migration in diamond is thermally activated above 600°C. Compared to low‐pressure high‐temperature (LPHT) annealing, high‐pressure and high‐temperature (HPHT) treatment allows for much higher annealing temperatures and longer durations, providing new opportunities to optimize key metrics of NV centers. This short review summarizes recent experimental progress in this direction. Dense NV centers with good spin coherence and single NV centers with excellent optical properties have been produced through HPHT growth and post‐treatment of single‐crystal diamonds. In addition, structural imaging, optical characterization, and DFT calculations provide further insights into the dynamics of defect migration under high‐temperature annealing. These results offer new perspectives on the fabrication of color centers in diamond and other wide‐gap semiconductor materials, including silicon carbide and hexagonal boron nitride, for advanced quantum applications.
Abstract Diamond hosts a wide variety of colour centres that have demonstrated outstanding optical and spin properties. Among them, the nitrogen-vacancy (NV) centre is by far the most investigated owing to its superior characteristics, which promise the development of highly sophisticated quantum devices, in particular for sensing applications. Nevertheless, harnessing the potential of these centres mainly relies on the availability of high quality and purity diamond single crystals that need to be specially designed and engineered for this purpose. Plasma assisted chemical vapour deposition (CVD) has become a key enabling technology in this field of research. Nitrogen can indeed be directly doped in situ into a high crystalline quality diamond matrix in a controlled way, allowing the production of single isolated centres or ensembles that can potentially be integrated into a device. In this paper we will provide an overview of the requirements for synthesizing ‘quantum-grade’ diamond films using CVD. These include the reduction of impurities and surrounding spins that limit coherence times, the control of NV density in a wide range of concentrations as well as their spatial localization within the diamond. Enhancing the charge state and preferential orientation of the colour centres is also discussed. These improvements in material fabrication have contributed to positioning diamond as one of the most promising solid-state quantum systems and the first industrial applications in sensing are just starting to emerge.
Abstract Single negatively charged nitrogen vacancy (NV−) centers in diamond have emerged as promising platforms for quantum information science, where long coherence times are essential for advancing quantum technologies. However, traditional fabrication methods often introduce lattice damage during the irradiation process used to create vacancies, significantly impairing the spin coherence properties of NV− centers. In this study, we systematically investigate high-pressure/high-temperature (HPHT) annealing as a non-destructive approach to generate high-coherence single NV− centers and elucidate the underlying mechanisms. Our results reveal that the distortion of the lattice field significantly influences the preferential formation of NV− centers at the interface of the 〈111〉-growth sector during diamond crystallization. Moreover, HPHT annealing effectively mobilizes nitrogen and vacancies, significantly promoting the formation of single NV− centers. This process also mitigates the influence of the distortion of the lattice field, resulting in a marked enhancement of coherence properties, with T 2 times reaching 578 μs. Notably, a naturally formed single NV− center in a low-stress region achieves an exceptional T 2 time of 721 μs, representing one of the highest values reported for diamonds with natural 13C abundance. Building on these insights, we have successfully achieved controlled, large-scale fabrication of high-coherence single NV− centers, providing essential guidance for future efforts to further enhance their coherence and establishing a robust foundation for their application in quantum technologies.
Negatively charged nitrogen-vacancy (NV − ) centres formed in diamond crystals are point defects that have potential applications in various quantum devices such as highly sensitive magnetic sensors. To improve the sensitivity of magnetic sensors using NV − centres, it is essential to precisely control the nitrogen concentration in the crystals. In this paper, we demonstrated that nitrogen concentration in diamond can be controlled with high precision for the following two representative growth methods. One is the high-pressure/high-temperature (HPHT) synthesis method and the other is the chemical vapour deposition (CVD) method. The nitrogen concentration of HPHT-grown diamond decreased semi-logarithmically with increasing contents of titanium or aluminium as nitrogen getter materials. The nitrogen concentration of CVD-grown diamond increased linearly with increasing the flow rate ratio of nitrogen to carbon. NV − centres were formed by controlling the total fluence of electron beams so that approximately 20% of the nitrogen became NV − centres. The coherence time of electron spin of NV − centres obtained by the Hahn-echo pulse sequence T 2 of these diamond crystals was inversely proportional to the nitrogen concentration. A comparison of T 2 of the NV − centres for HPHT-synthesized and CVD-grown diamonds showed no significant difference between them. This article is part of the Theo Murphy meeting issue ‘Diamond for quantum applications’.
Ensembles of nitrogen-vacancy (NV) centers in diamond are a leading platform for practical quantum sensors. Reproducible and scalable fabrication of NV-ensembles with desired properties is crucial. This work addresses these challenges by developing a chemical vapor deposition (CVD) synthesis process to produce diamond material at scale with improved NV-ensemble properties for a target NV density. The material reported in this work enables immediate sensitivity improvements for current devices. In addition, techniques established in this work for material and sensor characterization at different stages of the CVD synthesis process provide metrics for future efforts targeting other NV densities or sample geometries.