Researchers of China have fabricated silicon carbide nanopillar arrays achieving record photon count rates of approximately 1 Mcps for PL5 and 2 Mcps for PL6 centers. This architecture establishes a new standard for brightness in silicon carbide color centers while maintaining uniformity across the array. The work demonstrates external nanoscale nuclear-spin detection using these devices, positioning the nanopillars as robust components for future scanning quantum probes and scalable sensor networks.

Silicon Carbide Nanopillars Enhance Quantum Sensing Brightness

This level of photon emission is enabled by a fabrication process that precisely positions PL5 and PL6 centers at the core of 4H-SiC nanopillars, overcoming limitations of randomly distributed defects in earlier designs. The resulting architecture not only maximizes light capture but also maintains consistent brightness across the entire array, a critical factor for scalability. The fabrication relies on a self-aligned process coupled with localized oxygen ion implantation, allowing deterministic placement of the quantum emitters within the nanopillar structure.

Finite-difference time-domain simulations guided the design of the nanopillar geometry, optimizing the top radius and height to enhance photon collection efficiency with a 0.7 numerical aperture air objective. These simulations demonstrate the impact of nanopillar dimensions on light extraction, informing the precise fabrication parameters needed to achieve peak performance.

The resulting uniformity in brightness across the array distinguishes this approach from previous attempts, which often suffered from variations in signal strength between individual defects. Beyond increased brightness, the devices successfully demonstrated external nanoscale nuclear-spin detection using nuclear magnetic resonance (NMR). The team at the Laboratory of Spin Magnetic Resonance, Hefei, anticipates these nanopillars will serve as robust building blocks for future quantum technologies.

The University of Science and Technology of China team, including researchers from the Hefei National Laboratory, detailed their work in a recent publication, outlining the materials and methods used to create these advanced quantum sensors. The fabrication process uses the mature wafer-scale manufacturing capabilities of silicon carbide, offering a pathway toward cost-effective and reproducible device production. This contrasts with approaches relying on the integration of diamond quantum chips, which face challenges related to large-scale, single-crystal diamond availability.

Record Photon Counts Achieved in SiC Nanophotonic Arrays

This achievement surpasses previously reported rates in bulk silicon carbide crystals, which typically exhibit around 100 kilocounts per second, and establishes a new benchmark for brightness across all reported SiC color centers. Researchers achieved this performance by precisely positioning PL5 and PL6 defects within nanopillars, a feat enabled by combining a self-aligned fabrication process with localized oxygen ion implantation. The design of these nanophotonic arrays focuses on maximizing fluorescence collection efficiency, a technique previously applied to nitrogen-vacancy (NV) centers in diamond for biological magnetic resonance and scanning magnetic imaging.

The self-aligned fabrication process begins with the deposition of multiple layers, PMGI-SF6, PMMA-A4 and a conductive polymer, onto a silicon carbide substrate. Electron beam lithography is then employed to create nanoscale holes in the PMMA layer, defining the locations for the nanopillars. The resulting structures, with sidewall angles fixed at 78 degrees due to etching conditions were characterized using confocal microscopy and scanning electron microscopy, confirming the precise placement of PL5 and PL6 defects within the arrays.

“By positioning centers at these optimal sites, we observe photon count rates of ~1 Mcps (PL5) and ~2 Mcps (PL6) with near-identical brightness across the array,” the researchers report, highlighting the uniformity of the emission. The near-infrared optical properties of these SiC color centers offer additional advantages for biological applications, reducing phototoxicity and minimizing background fluorescence often encountered in living tissues.

This compatibility with optical fibers further expands the potential for remote sensing and in vivo measurements. The combination of high brightness, uniformity and scalable fabrication techniques positions these nanopillar arrays as practical building blocks for atomic force microscopy (AFM)-based quantum probes and large-scale nanoscale sensing networks.

Nanopillar Design Optimizes Photon Collection Efficiency

This level of control over structural parameters is critical, as simulations demonstrated a rapid decrease in efficiency with imperfect alignment of the color centers within the nanopillar structure. Specifically, the simulations showed that maintaining a doping region below 100 nanometers is essential for approaching optimal and uniform collection efficiency, a parameter directly addressed by the fabrication process. This precision is not merely academic; the simulations clearly illustrate the stark contrast between bulk SiC crystals, non-aligned nanopillars exhibiting random performance, and the optimized, uniform performance achieved in self-aligned nanopillars with a 90-nanometer doping region.

The impact of precise color center placement extends beyond simple brightness. The simulations reveal that lateral deviation from the nanopillar center significantly reduces collection efficiency. The analysis, detailed in accompanying supplementary material, demonstrates that a doping region exceeding 100 nanometers compromises the ability to achieve uniform performance.

This finding highlights the importance of the self-aligned fabrication technique in consistently delivering color centers within the optimal 90-nanometer radius, ensuring that each nanopillar functions as a highly efficient light emitter. The wavelength of the electric dipole was set to 1040 nanometers, closely matching the zero-phonon lines of both PL5 (1043 nm) and PL6 (1038 nm) to maximize signal detection. These parameters were carefully tuned to optimize the nanophotonic arrays for the specific emission wavelengths of the targeted silicon carbide defects.

This multi-step process, detailed in the materials and methods section, allows for the creation of highly uniform arrays with deterministic placement of the quantum emitters. Error bars representing standard errors of measured data are included in the reported results, demonstrating a commitment to rigorous data analysis.

Nanoscale NMR Detection Demonstrates External Spin Sensing

Researchers of China demonstrated external nanoscale nuclear-spin detection using newly fabricated silicon carbide nanopillar arrays, extending the capabilities of quantum sensing beyond static measurements. This achievement builds upon the creation of highly uniform and bright nanophotonic structures, a critical step toward practical, large-scale quantum devices.

The work directly addresses a long-standing challenge in the field: achieving scalable integration of color centers with consistent performance, a hurdle that previously limited the realization of robust quantum sensors. The resulting architecture, as detailed in the published findings, contrasts sharply with earlier methods that suffered from low photon collection or random performance due to misaligned emitters.

The successful application of these devices to nanoscale nuclear magnetic resonance (NMR) represents an advancement in external spin sensing. By demonstrating the ability to detect nuclear spins at the nanoscale under ambient conditions, the researchers have opened new avenues for investigating materials and biological systems with unprecedented resolution. The fabrication process, originating in the Laboratory of Spin Magnetic Resonance, involved spin-coating layers of materials and using electron beam lithography to create precise nanopillar patterns.

This multi-step process ensures the creation of highly uniform structures, essential for consistent performance across the array. The team’s commitment to achieving uniform performance is evident in the data, which demonstrates near-identical brightness across the fabricated devices. This consistency is a key differentiator, as it allows for reliable and reproducible measurements, a critical requirement for practical applications. The implications of this work extend beyond fundamental research, offering a promising route toward large-scale nanoscale quantum sensing.

👉 More information
🗞 Bright and Uniform Silicon Carbide Nanophotonic Arrays for Scalable Nanoscale Quantum Sensing
✍️ Chenyang Liao et al.
🧠 ArXiv: https://arxiv.org/html/2611.16252v1

More like this