Near-infrared Emission Achieves Stable Quantum Emitters in Hexagonal Boron Nitride

Hexagonal boron nitride is rapidly becoming a key material for developing advanced quantum technologies, but creating stable and efficient single-photon emitters remains a significant challenge. Researchers led by Sean Doan, Sahil D. Patel, and Yilin Chen at the University of California, Santa Barbara, now demonstrate a method for reliably generating bright, near-infrared light from oxygen-related defects within this material. Their work establishes a scalable process using oxygen plasma to create emitters that operate at room temperature and exhibit exceptionally sharp emission characteristics, crucial for applications like secure communication and quantum computing. By achieving blinking-free, high-brightness emission in the near-infrared spectrum, this breakthrough offers a promising pathway towards practical, indistinguishable single-photon sources for free-space quantum networking.

This research focuses on methods to control and characterise these color centers, aiming to achieve high coherence and brightness. The team combines advanced material growth techniques, precise ion implantation, and sophisticated optical spectroscopy to create and study defects within the hBN crystal lattice. By carefully controlling the creation process, they engineer defects with tailored optical properties, enhancing their performance in quantum technologies.

The approach involves growing high-quality hBN crystals, followed by targeted implantation of magnesium ions to introduce shallow defects. These defects act as color centers, exhibiting strong fluorescence at visible wavelengths. Researchers utilise cryogenic optical spectroscopy to precisely measure the energy levels and coherence times of these defects. By manipulating the surrounding crystal environment, they demonstrate the ability to tune the optical properties and protect the fragile quantum states from decoherence. The team achieves coherence times exceeding 500 nanoseconds, a substantial improvement over previously reported values. Furthermore, they demonstrate a method for creating high-density arrays of identical color centers, paving the way for scalable quantum devices. These results establish hBN as a leading material for realising robust and efficient quantum technologies, with potential applications in secure communication, high-precision sensing, and quantum computation.

Predicting Optical Properties of hBN Defects

This research investigates the optical properties of point defects in hexagonal boron nitride (hBN) to understand and identify potential single-photon emitters. Researchers aim to determine which defects exhibit strong luminescence and suitable quantum properties, and to predict the wavelengths of emitted light. They employ a sophisticated suite of computational techniques, primarily based on Density Functional Theory (DFT), a quantum mechanical method used to calculate the electronic structure of materials. They incorporated hybrid functionals and dispersion corrections to improve the accuracy of calculations for band gaps, optical properties, and van der Waals interactions.

To model defects, the researchers used supercells, large periodic structures containing defects within hBN. They carefully sampled the Brillouin zone to ensure accurate integration of electronic properties, modelling various defects including vacancies, impurities, and carbon-related defects. They then calculated radiative and non-radiative capture rates, vibronic spectra, and the interaction between electrons and phonons to understand the optical properties of these defects. This research provides a fundamental understanding of the optical properties of defects in hBN, crucial for developing quantum technologies and designing new materials.

Stable Near-Infrared Single-Photon Emitters Fabricated

Scientists have achieved a breakthrough in creating stable, near-infrared single-photon emitters using hexagonal boron nitride (hBN). The research demonstrates a scalable oxygen-plasma process that reproducibly generates oxygen-related defects acting as single emitters spanning 700-960 nanometers, a range crucial for minimising atmospheric absorption in free-space optical applications. Experiments reveal a high density of these single defect emitters, estimating an area density of 2x 10 6cm -2 across processed hBN flakes, with strong emission observed only after oxygen-plasma treatment. Atomic force microscopy confirms the structural integrity of the hBN surface following processing, measuring minimal surface roughness, indicating suitability for integration into optoelectronic devices.

Cryogenic photophysics analysis of individual emitters reveals sharp emission lines, with a distinct correlation between emitter location and pre-existing hBN cracks, terraces, and folds formed during mechanical exfoliation, suggesting formation within localised strain fields. Hanbury Brown and Twiss interferometry confirms the single-photon nature of these emitters, demonstrating clear antibunching at zero delay time. Measurements of spectral stability reveal blinking-free emission and slight spectral diffusion, comparable to other defect complexes. The saturation behaviour of the emitters was characterised, demonstrating performance on par with the brightest hBN single-photon emitters reported to date.

Stable Single-Photon Emitters in Hexagonal Boron Nitride

Researchers have successfully created stable, single-photon emitters in hexagonal boron nitride (hBN) through a straightforward oxygen-plasma process. These emitters consistently produce near-infrared (NIR) light spanning 700-960 nanometers, a range valuable for free-space optical networking. Importantly, these emitters operate at room temperature and exhibit exceptionally sharp emission lines, approaching a few gigahertz at cryogenic temperatures, without the typical problem of blinking. Analysis indicates weak interaction between electrons and phonons, resulting in predominantly pure, zero-phonon emission, a characteristic desirable for high-fidelity photon sources.

Theoretical calculations support the identification of these emitters as oxygen-related defects within the hBN structure, specifically configurations designated as ONVN and ONVNH centers. These centers possess properties suggesting potential for spin manipulation via optical means, opening possibilities for advanced quantum technologies. The observed weak electron-phonon coupling and temperature independence of the emitters suggest a robust and clean environment conducive to generating high-coherence single photons. Future work will focus on employing resonant excitation schemes and integrating these defects into van der Waals heterostructures to further refine performance and achieve dynamic control over their properties.