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arXiv:2507.14047 · Frontiers in Quantum Science and Technology

Fabrication of oriented NV center arrays in diamond via femtosecond laser writing and reorientation

Kai Klink, Andrew Raj Kirkpatrick, Yukihiro Tadokoro, Jonas N. Becker, Shannon S. Nicley

Published Sep 23, 2025• 7 citations

Abstract

Introduction Nitrogen-vacancy (NV) centers in diamond are widely recognized as highly promising solid-state quantum sensors due to their long room temperature coherence times and atomic-scale size, which enable exceptional sensitivity and nanoscale spatial resolution under ambient conditions. Ultrafast laser writing has demonstrated the deterministic spatial control of individual NV− centers, however, the resulting random orientation of the defect axis limits the magnetic field sensitivity and signal contrast. Methods We developed an all-optical approach for reorienting laser-written NV− centers to lie along a specific crystallographic axis using femtosecond laser annealing. The orientation is determined by polarization analysis, and the annealing and subsequent polarization analysis are repeated until the desired orientation is observed. Results Our method achieves deterministic alignment of NV− centers along the optical axis in (111)-oriented diamond substrates and allows selection between two observable orientation classes in (100)-oriented substrates. The reorientation preserves spatial ordering while producing uniform orientation across arrays of NV− centers. Discussion This approach enables scalable fabrication of orientation-controlled NV− arrays, and paves the way for scalable, high performance quantum devices based on orientation-controlled NV− centers.

DOI: 10.3389/frqst.2025.1667545

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Nitrogen-vacancy centers in diamond have gained widespread attention as quantum systems that can be applied in quantum information devices. The excellent properties of quantum devices can be enhanced using preferentially oriented nitrogen-vacancy (NV) centers. However, thus far, orientation control has been achieved only via chemical vapor deposition. In this study, we demonstrate the creation of preferentially oriented NV centers via laser writing. The alignment ratio of ensemble NV centers is biased along the direction parallel to [111], depending on the femtosecond laser polarization, causing an increase of 55% in contrast to the optically magnetic resonance signal at maximum compared with 25% in random orientation. Based on time-dependent density-functional theory (TDDFT) simulations and experimental observations, such complex polarization dependence can be attributed to the anisotropy of electron excitation. This technique provides a new optical fabrication method for engineered materials and devices used in quantum technology.

Nitrogen-Vacancy (NV) centers in diamond are expected as highly sensitive magnetic sensors operable at room temperature. One major challenge in improving sensitivity is controlling the NV axis orientation. In diamond crystals, NV centers are typically randomly oriented along four crystallographic axes. Since only NV centers on a specific axis are utilized, NV centers on other axes act as fluorescence noise. Therefore, selectively forming NV centers along a single crystallographic axis is expected to enhance sensitivity. Perfectly oriented NV centers can be fabricated by nitrogen doping during chemical vapor deposition (CVD) growth, however, achieving a high NV center density remains challenging. In contrast, a high NV center density can be achieved by electron-beam irradiation followed by post-annealing, although orientation control remains difficult. In this study, we attempted to control NV center orientation by applying microwave annealing after electron-beam irradiation. Generally, microwave irradiation of material induces heating via Joule, dielectric and magnetic losses. Diamond has negligible dielectric and magnetic losses, so a boron doped diamond layer was formed as conductive layer and microwave annealing was performed via Joule loss. Because the conductive layer is thin, an electric field is applied throughout the whole diamond, resulting in a drift current flowing across the diamond. We thought that by controlling this current in the [111] direction, it would be possible to preferentially form [111]-oriented NV centers.

Diamond's nitrogen vacancy (NV) center is an optically active defect with long spin coherence times, showing great potential for both efficient nanoscale magnetometry and quantum information processing schemes. Recently, both the formation of buried 3D optical waveguides and high-quality single NVs in diamond were demonstrated using the versatile femtosecond laser-writing technique. However, until now, combining these technologies has been an outstanding challenge. In this Letter, we fabricate laser-written photonic waveguides in quantum grade diamond which are aligned to within micron resolution to single laser-written NVs, enabling an integrated platform providing deterministically positioned waveguide-coupled NVs. This fabrication technology opens the way toward on-chip optical routing of single photons between NVs and optically integrated spin-based sensing.

Nitrogen-vacancy (NV) centers in diamond have attracted significant interest because of their excellent spin and optical characteristics for quantum information and metrology. To exploit these characteristics, precise control of the orientation of the NV axis in the lattice is essential. Here we show that the orientation of more than 99% of the NV centers can be aligned along the [111] axis by chemical vapor deposition homoepitaxial growth on (111) substrates. We also discuss the alignment mechanisms. Our result enables a fourfold improvement in the magnetic field sensitivity and opens new avenues to the optimum design of NV center devices.

Diamond's nitrogen vacancy (NV) center is an optically active defect with long spin coherence times, showing potential for efficient nanoscale magnetometry and entanglement schemes. Recently, both the formation of buried 3D optical waveguides and high quality single NVs in diamond were demonstrated using femtosecond laser-writing. However, until now, combining these technologies has been an outstanding challenge. In this work, we fabricate laser-written photonic circuits in diamond aligned within micron resolution to single laser-written NVs, enabling an integrated platform providing deterministically positioned waveguide-coupled NVs. This fabrication technology opens the way towards on-chip optical routing of single photons between NVs and optically integrated spin-based magnetometry.

Nitrogen-vacancy (NV) color centers in diamond are excellent quantum sensors possessing high sensitivity and nano-scale spatial resolution. Their integration in photonic structures is often desired, since it leads to an increased photon emission and also allows the realization of solid-state quantum technology architectures. Here, we report the fabrication of diamond nano-pillars with diameters up to 1000 nm by electron beam lithography and inductively coupled plasma reactive ion etching in nitrogen-rich diamonds (type Ib) with [100] and [111] crystal orientations. The NV centers were created by keV-He ion bombardment and subsequent annealing, and we estimate an average number of NVs per pillar to be 4300 ± 300 and 520 ± 120 for the [100] and [111] samples, respectively. Lifetime measurements of the NVs’ excited state showed two time constants with average values of τ1 ≈ 2 ns and τ2 ≈ 8 ns, which are shorter as compared to a single color center in a bulk crystal (τ ≈ 10 ns). This is probably due to a coupling between the NVs as well as due to interaction with bombardment-induced defects and substitutional nitrogen (P1 centers). Optically detected magnetic resonance measurements revealed a contrast of about 5% and average coherence and relaxation times of T2 [100] = 420 ± 40 ns, T2 [111] = 560 ± 50 ns, and T1 [100] = 162 ± 11 μs, T1 [111] = 174 ± 24 μs. These pillars could find an application for scanning probe magnetic field imaging.