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arXiv:2511.15170

Intelligent Inverse Design of Multi-Layer Metasurface Cavities for Dual Resonance Enhancement of Nanodiamond Single Photon Emitters

Omar A. M. Abdelraouf

physics.opticsquant-phSubmitted Nov 19, 2025• Announced Nov 20, 2025
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Abstract

Single-photon emitters (SPEs) based on nitrogen-vacancy centers in nanodiamonds (neutral NV0 (wavelength 575 nm) and negative NV- (wavelength 637 nm)) represent promising platforms for quantum nanophotonics applications, yet their emission efficiencies remain constrained by weak light-matter interactions. Multi-layer metasurfaces (MLM) offer unprecedented degrees of freedom for efficient light manipulation beyond conventional single-material metasurfaces, enabling dual-resonance cavities that can simultaneously enhance pump excitation and SPE collection. However, traditional trial-and-error and forward optimization methods face significant challenges in designing these complex structures due to the vast parameter space and computational demands. Here, we present NanoPhotoNet-Inverse, an artificial intelligence-driven inverse design framework based on a hybrid deep neural network architecture. This model efficiently performs inverse design of two dual-resonance MLM cavities to amplify pump and SPE emissions of different vacancies in nanodiamond and improve SPE collection. Our approach achieves inverse design prediction efficiency exceeding 98.7%, demonstrating three orders of magnitude amplification in SPE count rate and 50 picosecond lifetime, significantly surpassing conventional cavity designs. These remarkable enhancements in emission rates and collection efficiency position our platform as a transformative technology for advancing quantum communication networks, quantum computing architectures, quantum sensing applications, and quantum cryptography systems. Therefore, it opens new pathways for intelligent photonic device engineering in quantum technologies.

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The nitrogen vacancy center in diamond in its negative charge state is a promising candidate for quantum optic experiments that require single photon emitters. Important benefits of the NV center are its high brightness and photo-stability, even at room temperature. Engineering the emission properties of NV centers with optical resonators is a widely followed approach to meet the requirements for quantum technological applications, but the effect on non-radiative decay paths is yet to be understood. Here we report on modifying the internal quantum efficiency of a single NV center in a nanodiamond coupled to a 1D photonic crystal cavity. We assess the Purcell enhancement via three independent measurement techniques and perform autocorrelation measurements at elevated excitation powers in confocal microscopy. Employing a three-level model allows us to extract the setup efficiency, individual transition rates and thus the internal quantum efficiency of our system. Combining our results, we find that the enhancement of the radiative decay rate via the Purcell effect results in an internal quantum efficiency of 90 % for cavity-coupled NV centers. Our findings will facilitate the realization of nano-scale single photon sources with near-unity internal quantum efficiencies operating at high repetition rates.

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Single-photon emitters (SPEs) based on nitrogen-vacancy centers in nanodiamonds (neutral NV0 (wavelength 575 nm) and negative NV- (wavelength 637 nm)) represent promising platforms for quantum nanophotonics applications, yet their emission efficiencies remain constrained by weak light-matter interactions. Multi-layer metasurfaces (MLM) offer unprecedented degrees of freedom for efficient light manipulation beyond conventional single-material metasurfaces, enabling dual-resonance cavities that can simultaneously enhance pump excitation and SPE collection. However, traditional trial-and-error and forward optimization methods face significant challenges in designing these complex structures due to the vast parameter space and computational demands. Here, we present NanoPhotoNet-Inverse, an artificial intelligence-driven inverse design framework based on a hybrid deep neural network architecture. This model efficiently performs inverse design of two dual-resonance MLM cavities to amplify pump and SPE emissions of different vacancies in nanodiamond and improve SPE collection. Our approach achieves inverse design prediction efficiency exceeding 98.7%, demonstrating three orders of magnitude amplification in SPE count rate and 50 picosecond lifetime, significantly surpassing conventional cavity designs. These remarkable enhancements in emission rates and collection efficiency position our platform as a transformative technology for advancing quantum communication networks, quantum computing architectures, quantum sensing applications, and quantum cryptography systems. Therefore, it opens new pathways for intelligent photonic device engineering in quantum technologies.
Nonlinear 2D materials such as 3R-phase molybdenum disulfide (3R-MoS2) offer strong second-order optical nonlinearities in an atomically thin platform, making them attractive for on-chip frequency conversion, quantum light generation, and integrated nonlinear nanophotonics. However, the second harmonic generation (SHG) efficiency of monolayer or few-layer 3R-MoS2 deposited on planar substrates remains fundamentally limited by weak light-matter interaction, poor phase matching, and small interaction volumes. Here, we introduce NanoPhotoNet-PINL, a physics informed AI-driven inverse design framework based on a hybrid one-dimensional convolutional neural network and deep neural network autoencoder, tailored for nonlinear MLMs metasurfaces. The model directly maps target dual-resonant reflection spectra at the fundamental and second-harmonic wavelengths to the required multi-layer geometries and material compositions that maximize the effective nonlinear overlap with an embedded 3R-MoS2 sheet. By integrating Maxwell-based nonlinear electrodynamics into the inverse design loop, we compute the second-harmonic conversion efficiency and modal overlap factors for each predicted MLMs design, enabling physics-guided training and evaluation. Our approach achieves an inverse-design prediction efficiency exceeding ~99.2 % along the linear spectral manifold, while the optimized dual-resonant MLMs yield more than three orders of magnitude enhancement in SHG intensity compared to a bare 3R-MoS2 flake on a planar substrate. NanoPhotoNet-PINL establishes a generalizable paradigm for intelligent inverse design of nonlinear multi-layer metasurfaces and phase-matched dual-resonant cavities for high-efficiency second-order processes.
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.
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 SiO2_22​ above a silver reflector, allows us to perform spectroscopic characterisation at 16 K and measure autocorrelation functions confirming single-photon emission (g2^22(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.
The realization of a scalable quantum internet requires efficient light-matter interfaces that map stationary qubits onto photonic carriers for long-distance transmission. A central challenge is the generation of entangled photons simultaneously compatible with single-emitter transitions and low-loss telecom fiber infrastructure. Spontaneous parametric down-conversion in integrated photonic platforms offers a promising route toward this goal. Among available material systems, AlGaAs is particularly attractive due to its large second-order nonlinearity and strong potential for monolithic integration. However, engineering the spectral and spatial properties of the generated quantum states requires the simultaneous optimization of numerous geometric and material parameters, a task remaining computationally demanding for conventional numerical approaches. To address this challenge and enable rapid and high-fidelity modeling of complex nonlinear photonic devices, we develop an inverse-design framework based on neural network surrogate models. Using this readily extendable method, we design a transversely pumped AlGaAs waveguide microcavity that produces polarization-entangled photon pairs in distinct spatial modes and frequency channels, one at 1092 nm, resonant with a 88Sr+^{88}\text{Sr}^{+}88Sr+ transition, and the other at 1550 nm in the telecom C-band. This device establishes a direct photonic interface between trapped-ion qubits and long-haul fiber networks, providing a scalable pathway toward hybrid quantum network architectures.
Manipulating photoluminescence from solid-state quantum emitters (QEs) on demand is of central importance for advanced quantum nanophotonic technologies. In comparison with conventional free-space approaches relying on bulky optical components, emitter-integrated metasurfaces provide a compact and efficient route for shaping photon emission directly at the source. Recent progress has established a common platform in which QE-excited surface plasmon polaritons (SPPs) are transformed by surrounding metasurfaces into free-space radiation with tailored propagation direction, polarization state, relative intensity, and spatial structure. This review highlights two complementary strategies that have recently been utilized for shaping quantum emission. The first is emitter-coupled meta-optics, which enables versatile photon sources with arbitrary polarization states, off-normal directionality, and multichannel emission by means of phase-engineered anisotropic meta-atoms. The second is vectorial scattering holography, including multiplexed implementations, which allows direct reconstruction of arbitrarily structured and polarization-multiplexed emission from individual nanodiamonds. Together, these approaches unlock unprecedented degrees of freedom for nanoscale light shaping and provide a promising route toward scalable quantum photonic devices and high-capacity information processing.
The nitrogen vacancy center in diamond in its negative charge state is a promising candidate for quantum optic experiments that require single photon emitters. Important benefits of the NV center are its high brightness and photo-stability, even at room temperature. Engineering the emission properties of NV centers with optical resonators is a widely followed approach to meet the requirements for quantum technological applications, but the effect on non-radiative decay paths is yet to be understood. Here we report on modifying the internal quantum efficiency of a single NV center in a nanodiamond coupled to a 1D photonic crystal cavity. We assess the Purcell enhancement via three independent measurement techniques and perform autocorrelation measurements at elevated excitation powers in confocal microscopy. Employing a three-level model allows us to extract the setup efficiency, individual transition rates and thus the internal quantum efficiency of our system. Combining our results, we find that the enhancement of the radiative decay rate via the Purcell effect results in an internal quantum efficiency of 90 % for cavity-coupled NV centers. Our findings will facilitate the realization of nano-scale single photon sources with near-unity internal quantum efficiencies operating at high repetition rates.