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arXiv:2508.06424

Single photon emission from lithographically-positioned engineered nanodiamonds for cryogenic applications

Tiwari, Vivekanand, Zhaojin Liu, Hao‐Cheng Weng, Krishna C. Balram, John Rarity, Soumen Mandal, Oliver Aneurin Williams, Gavin W. Morley, Joe A. Smith

Published Aug 8, 2025• 0 citations

Abstract

Nitrogen-vacancy centres in nanodiamonds (NDs) provide a promising resource for quantum photonic systems. However, developing a technology beyond proof-of-principle physics requires optimally engineering its component parts. In this work, we present a hybrid materials platform by photolithographically positioning ball-milled isotopically-enriched NDs on broadband metal reflectors. The structure enhances the photonic collection efficiency, enabling cryogenic characterisation despite the limited numerical aperture imposed by our cryostat. Our device, with SiO$_2$ above a silver reflector, allows us to perform spectroscopic characterisation at 16 K and measure autocorrelation functions confirming single-photon emission (g$^2$(0)<0.5). Through comparative studies of similar hybrid device configurations, we can move towards optimally engineered techniques for building and analysing quantum emitters in wafer-scale photonic environments.

DOI: 10.48550/arxiv.2508.06424

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Nitrogen-vacancy centres in nanodiamonds (NDs) provide a promising resource for quantum photonic systems. However, developing a technology beyond proof-of-principle physics requires optimally engineering its component parts. In this work, we present a hybrid materials platform by photolithographically positioning ball-milled isotopically-enriched NDs on broadband metal reflectors. The structure enhances the photonic collection efficiency, enabling cryogenic characterisation despite the limited numerical aperture imposed by our cryostat. Our device, with SiO

_2

above a silver reflector, allows us to perform spectroscopic characterisation at 16 K and measure autocorrelation functions confirming single-photon emission (g

_2

(0)<0.5). Through comparative studies of similar hybrid device configurations, we can move towards optimally engineered techniques for building and analysing quantum emitters in wafer-scale photonic environments.

Single-photon sources are essential for quantum technologies, supporting secure communication, quantum computing, and integrated photonic systems. Nitrogen-vacancy (NV) centers in nanodiamonds are robust emitters that operate at room temperature and can be positioned on-chip, but efficient coupling to photonic modes remains challenging. We present the design, fabrication, and experimental characterization of a silicon nitride photonic structure engineered to enhance and extract emission from NV centers. The device features a subwavelength gap between waveguides, a Bragg reflector for emission redirection, and an output waveguide for collection. Simulations guided the optimization of the geometry to increase the spontaneous emission rate through photonic confinement. Nanodiamonds were deposited into the gap using lithographic patterning and drop-casting. Fluorescence lifetime measurements confirm that the structure modifies the emission dynamics of the NV centers. The approach is compatible with scalable fabrication techniques and offers a practical route toward integrated, chip-based single-photon sources.

Finding the right material platform for engineering efficient photonic interfaces to solid state emitters has been a long-standing bottleneck for scaling up solid state quantum systems. In this work, we demonstrate that nitrogen rich silicon nitride, with its low auto-fluorescence at visible wavelengths, is a viable quantum photonics platform by showing that nitrogen vacancy centers embedded in nanodiamonds preserve both their quantum optical and spin properties post-encapsulation. Given the variety of high-performance photonic components already demonstrated in silicon nitride, our work opens up a promising avenue for building integrated photonic platforms using solid state emitters.

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