Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2605.16596

Optimization of circular cavities via guided-mode expansion method based inverse design

Abhishek Das, Neelesh Kumar Vij, Demitry Farfurnik

quant-phphysics.opticsSubmitted May 15, 2026• Announced May 19, 2026
arXivHTMLPDF

Abstract

Spin-photon interfaces, realized by coupling optically active spin systems to photonic cavities, are essential for quantum networking and quantum information processing. Implementing such an interface for polarization-encoded photons requires a cavity that supports arbitrary polarization, provides efficient optical access through its far-field mode, and maintains sufficiently high quality factors to enable high cooperativity with the system's optical transitions. However, inherent trade-offs between the Q-factor and far-field emission mode make the simultaneous optimization of these parameters toward the realization of spin-photon interfaces challenging. In this work, we implement a gradient-based inverse-design framework using guided-mode expansion with automatic differentiation to obtain the geometrical features of a circular ring cavity that supports arbitrary polarization while simultaneously optimizing the cavity quality factor and far-field mode profile. The resulting optimized non-periodic cavity achieves a quality factor of approximately $9,000$, about an order-of-magnitude higher than that of a periodic ("bullseye") cavity while preserving a Gaussian-like far-field emission pattern. Furthermore, by varying the cavity geometry within a $\pm 6$ nm fabrication tolerance, we demonstrate the robustness of the design against fabrication errors and identify the innermost ring width and central disk radius as the parameters with the greatest impact on the quality factor and far-field mode. These results establish guided mode expansion-based inverse design as a powerful and computationally efficient approach for developing high-cooperativity spin-photon interfaces for quantum photonic applications.

Comments
10 pages, 4 figures,

Related papers

Inverse-Designed Nanobeam Cavities for High-Cooperativity Spin-Photon Interfaces in Silicon

Nail Letty, Md Sakibul Islam, Wayesh Qarony

Telecom-band spin defects in silicon offer a compelling platform for integrated quantum networks by combining scalable silicon photonics with spin-based quantum memories and multiqubit registers. The T center and recently demonstrated Al1 center are particularly promising, but their limited coherent zero-phonon emission requires strong cavity enhancement for efficient spin-photon interfaces. Here, we inverse-design silicon nanobeam cavities for both centers using a unified adjoint-optimization framework targeting Purcell enhancement, resonance alignment, and photon extraction. For each emitter, symmetric cavities maximize Purcell enhancement, while asymmetric cavities provide directional coupling to an integrated waveguide. Three-dimensional finite-difference time-domain simulations yield loaded quality factors up to 3.25 x 10^6, Purcell factors up to 1.43 x 10^5, and cooperativities of approximately 280-5000, corresponding to cavity-coupled emission fractions exceeding 99.6%. The asymmetric cavities direct approximately 90% of emitted power into a single on-chip waveguide while maintaining cooperativity above 280. Under nanometer-scale fabrication perturbations, all four designs remain within the high-cooperativity regime, and high cooperativity persists when the cavity quality factor is constrained to a realistic absorption-limited value of 10^5. This unified, fabrication-compatible framework establishes a scalable cavity-design route for silicon telecom spin-photon interfaces and, to our knowledge, the first cavity designs for the Al1 center.

quant-pharXiv:2609.32205•Sep 29, 2026

Optimal design of diamond-air microcavities for quantum networks using an analytical approach

Suzanne B. van Dam, Maximilian Ruf, Ronald Hanson

Defect centres in diamond are promising building blocks for quantum networks thanks to a long-lived spin state and bright spin-photon interface. However, their low fraction of emission into a desired optical mode limits the entangling success probability. The key to overcoming this is through Purcell enhancement of the emission. Open Fabry–Perot cavities with an embedded diamond membrane allow for such enhancement while retaining good emitter properties. To guide the focus for design improvements it is essential to understand the influence of different types of losses and geometry choices. In particular, in the design of these cavities a high Purcell factor has to be weighed against cavity stability and efficient outcoupling. To be able to make these trade-offs we develop analytic descriptions of such hybrid diamond-and-air cavities as an extension to previous numeric methods. The insights provided by this analysis yield an effective tool to find the optimal design parameters for a diamond-air cavity.

arXiv:1806.11474•New Journal of Physics•Oct 29, 2018•30 citations

Engineering Chiral Light–Matter Interactions in a Waveguide-Coupled Nanocavity

D. Hallett, Andrew P. Foster, David M. Whittaker +2 more

High Resolution Image Download MS PowerPoint Slide Spin-dependent, directional light–matter interactions form the basis of chiral quantum networks. In the solid state, quantum emitters commonly possess circularly polarized optical transitions with spin-dependent handedness. We demonstrate numerically that spin-dependent chiral coupling can be realized by embedding such an emitter in a waveguide-coupled nanocavity, which supports two near-degenerate, orthogonally polarized cavity modes. The chiral behavior arises due to direction-dependent interference between the cavity modes upon coupling to two single-mode output waveguides. Notably, an experimentally realistic cavity design simultaneously supports near-unity chiral contrast, efficient (>95%) cavity-waveguide coupling and enhanced light–matter interaction strength (Purcell factor F P > 70). In combination, these parameters enable the development of highly coherent spin–photon interfaces ready for integration into nanophotonic circuits.

arXiv:2108.01462•ACS Photonics•Jan 26, 2022•26 citations

Efficient spin-photon interface for solid-state-based spin systems for quantum information processing and enhanced metrology

Jiabao Zheng

The holy grail for quantum engineers and scientists is to build the quantum internet that spans over the entire globe. This information infrastructure holds the promise for transmitting information securely, scaling up computing power exponentially and setting the standards for precision measurement at the ultimate limit. Solid-state-based spin systems recently emerge as promising building blocks for the quantum internet. Among these candidates, the negatively charged nitrogen vacancy (NV) center in diamond attracted much attention thanks to its optical addressability, long spin coherence times, and well-controlled electronic orbitals and spin states. However, the non-ideal optical properties of NV poses a challenge to its implementation in quantum technologies. This calls for building photonic structures as efficient spin-photon interfaces for realizing strong interactions with photon modes or efficient out-coupling of its fluorescence. Such interfacing structures are also of great importance for other optically active spin-systems newly found. In this dissertation, chirped dielectric cavities are designed for building NV as fast single photon sources via broadband Purcell enhancement, using an inverse simulation approach to maximize the broadband absorption of the atomically thin absorbers. Simulated NV-cavity coupling indicates broadband Purcell factor of ∼> 100. Next, to realize coupled NV-cavity systems over large scale, a self-aligned nano-implantation technique is investigated using a lithographically defined hybrid mask for both precision pattern transfer and nitrogen implantation. Measured results show single-NV per cavity yield of ∼ 26±1% and 5-fold Purcell induced intensity enhancement. Finally, chirped circular gratings are designed for efficient collection from the NV for remote entanglement and precision sensing. Simulated grating structures present near-unity collection efficiencies. These demonstrated techniques and structures are also applicable to other solid-state-based spin systems.

•Jan 1, 2017•0 citations

A Broadband Nanowire Quantum Dot Cavity Design for the Efficient Extraction of Entangled Photons

Sayan Gangopadhyay, Sasan V. Grayli, Sathursan Kokilathasan +1 more

A bright source of on-demand entangled photons is needed for quantum networks. A single quantum dot in a site-selected nanowire waveguide is a promising candidate for realizing such sources. However, such sources are associated with poor single-photon indistinguishability, limiting their applicability in quantum networks. A common approach for enhancing the single-photon indistinguishability in quantum dot-based entangled photon sources is to implement a broadband optical cavity. Achieving a high-Purcell cavity while retaining the advantages of the nanowire, such as directional emission, a broad operational bandwidth, and high light extraction efficiency, has been a significant challenge. Here, we propose a nanowire cavity based on quasi-bound states in the continuum formed by the strong coupling of two resonant optical modes. We numerically predict this design to support a cavity mode with 4 nm bandwidth and a Purcell enhancement of $\sim$17. This cavity mode enables a directional far-field emission profile (88% overlap with a Gaussian) with a light extraction efficiency of $\sim$74%. Our solution opens up a route for generating entangled photon pairs with enhanced extraction efficiency and single-photon indistinguishability for the practical realization of quantum networks.

quant-pharXiv:2601.04440•Jan 9, 2026

Optical spin initialization and readout with a cavity-coupled quantum dot in an in-plane magnetic field

Samuel J. Sheldon, Alistair J. Brash, Maurice S. Skolnick +2 more

The spin of a charged semiconductor quantum dot (QD) coupled to an optical cavity is a promising candidate for high-fidelity spin-photon interfaces; the cavity selectively modifies the decay rates of optical transitions such that spin initialization, manipulation, and readout are all possible in a single magnetic field geometry. By performing cavity QED calculations, we show that a cavity with a single, linearly polarized mode can simultaneously support both high-fidelity optical spin initialization and readout in a single, in-plane (Voigt geometry) magnetic field. Furthermore, we demonstrate that single-mode cavities always outperform bimodal cavities in experimentally favorable driving regimes. Our analysis, when combined with established methods of control in a Voigt geometry field, provides optimal parameter regimes for high-fidelity initialization and readout, and coherent control in both cavity configurations, providing insights for the design and development of QD spin-photon interfaces as the basis of quantum network nodes and for the generation of photonic graph states. Published by the American Physical Society 2024

arXiv:2206.11008•Physical review. B./Physical review. B•Dec 10, 2024•0 citations
Spin-photon interfaces, realized by coupling optically active spin systems to photonic cavities, are essential for quantum networking and quantum information processing. Implementing such an interface for polarization-encoded photons requires a cavity that supports arbitrary polarization, provides efficient optical access through its far-field mode, and maintains sufficiently high quality factors to enable high cooperativity with the system's optical transitions. However, inherent trade-offs between the Q-factor and far-field emission mode make the simultaneous optimization of these parameters toward the realization of spin-photon interfaces challenging. In this work, we implement a gradient-based inverse-design framework using guided-mode expansion with automatic differentiation to obtain the geometrical features of a circular ring cavity that supports arbitrary polarization while simultaneously optimizing the cavity quality factor and far-field mode profile. The resulting optimized non-periodic cavity achieves a quality factor of approximately 9,0009,0009,000, about an order-of-magnitude higher than that of a periodic ("bullseye") cavity while preserving a Gaussian-like far-field emission pattern. Furthermore, by varying the cavity geometry within a ±6\pm 6±6 nm fabrication tolerance, we demonstrate the robustness of the design against fabrication errors and identify the innermost ring width and central disk radius as the parameters with the greatest impact on the quality factor and far-field mode. These results establish guided mode expansion-based inverse design as a powerful and computationally efficient approach for developing high-cooperativity spin-photon interfaces for quantum photonic applications.
Telecom-band spin defects in silicon offer a compelling platform for integrated quantum networks by combining scalable silicon photonics with spin-based quantum memories and multiqubit registers. The T center and recently demonstrated Al1 center are particularly promising, but their limited coherent zero-phonon emission requires strong cavity enhancement for efficient spin-photon interfaces. Here, we inverse-design silicon nanobeam cavities for both centers using a unified adjoint-optimization framework targeting Purcell enhancement, resonance alignment, and photon extraction. For each emitter, symmetric cavities maximize Purcell enhancement, while asymmetric cavities provide directional coupling to an integrated waveguide. Three-dimensional finite-difference time-domain simulations yield loaded quality factors up to 3.25 x 10^6, Purcell factors up to 1.43 x 10^5, and cooperativities of approximately 280-5000, corresponding to cavity-coupled emission fractions exceeding 99.6%. The asymmetric cavities direct approximately 90% of emitted power into a single on-chip waveguide while maintaining cooperativity above 280. Under nanometer-scale fabrication perturbations, all four designs remain within the high-cooperativity regime, and high cooperativity persists when the cavity quality factor is constrained to a realistic absorption-limited value of 10^5. This unified, fabrication-compatible framework establishes a scalable cavity-design route for silicon telecom spin-photon interfaces and, to our knowledge, the first cavity designs for the Al1 center.
Defect centres in diamond are promising building blocks for quantum networks thanks to a long-lived spin state and bright spin-photon interface. However, their low fraction of emission into a desired optical mode limits the entangling success probability. The key to overcoming this is through Purcell enhancement of the emission. Open Fabry–Perot cavities with an embedded diamond membrane allow for such enhancement while retaining good emitter properties. To guide the focus for design improvements it is essential to understand the influence of different types of losses and geometry choices. In particular, in the design of these cavities a high Purcell factor has to be weighed against cavity stability and efficient outcoupling. To be able to make these trade-offs we develop analytic descriptions of such hybrid diamond-and-air cavities as an extension to previous numeric methods. The insights provided by this analysis yield an effective tool to find the optimal design parameters for a diamond-air cavity.
High Resolution Image Download MS PowerPoint Slide Spin-dependent, directional light–matter interactions form the basis of chiral quantum networks. In the solid state, quantum emitters commonly possess circularly polarized optical transitions with spin-dependent handedness. We demonstrate numerically that spin-dependent chiral coupling can be realized by embedding such an emitter in a waveguide-coupled nanocavity, which supports two near-degenerate, orthogonally polarized cavity modes. The chiral behavior arises due to direction-dependent interference between the cavity modes upon coupling to two single-mode output waveguides. Notably, an experimentally realistic cavity design simultaneously supports near-unity chiral contrast, efficient (>95%) cavity-waveguide coupling and enhanced light–matter interaction strength (Purcell factor F P > 70). In combination, these parameters enable the development of highly coherent spin–photon interfaces ready for integration into nanophotonic circuits.
The holy grail for quantum engineers and scientists is to build the quantum internet that spans over the entire globe. This information infrastructure holds the promise for transmitting information securely, scaling up computing power exponentially and setting the standards for precision measurement at the ultimate limit. Solid-state-based spin systems recently emerge as promising building blocks for the quantum internet. Among these candidates, the negatively charged nitrogen vacancy (NV) center in diamond attracted much attention thanks to its optical addressability, long spin coherence times, and well-controlled electronic orbitals and spin states. However, the non-ideal optical properties of NV poses a challenge to its implementation in quantum technologies. This calls for building photonic structures as efficient spin-photon interfaces for realizing strong interactions with photon modes or efficient out-coupling of its fluorescence. Such interfacing structures are also of great importance for other optically active spin-systems newly found. In this dissertation, chirped dielectric cavities are designed for building NV as fast single photon sources via broadband Purcell enhancement, using an inverse simulation approach to maximize the broadband absorption of the atomically thin absorbers. Simulated NV-cavity coupling indicates broadband Purcell factor of ∼> 100. Next, to realize coupled NV-cavity systems over large scale, a self-aligned nano-implantation technique is investigated using a lithographically defined hybrid mask for both precision pattern transfer and nitrogen implantation. Measured results show single-NV per cavity yield of ∼ 26±1% and 5-fold Purcell induced intensity enhancement. Finally, chirped circular gratings are designed for efficient collection from the NV for remote entanglement and precision sensing. Simulated grating structures present near-unity collection efficiencies. These demonstrated techniques and structures are also applicable to other solid-state-based spin systems.
A bright source of on-demand entangled photons is needed for quantum networks. A single quantum dot in a site-selected nanowire waveguide is a promising candidate for realizing such sources. However, such sources are associated with poor single-photon indistinguishability, limiting their applicability in quantum networks. A common approach for enhancing the single-photon indistinguishability in quantum dot-based entangled photon sources is to implement a broadband optical cavity. Achieving a high-Purcell cavity while retaining the advantages of the nanowire, such as directional emission, a broad operational bandwidth, and high light extraction efficiency, has been a significant challenge. Here, we propose a nanowire cavity based on quasi-bound states in the continuum formed by the strong coupling of two resonant optical modes. We numerically predict this design to support a cavity mode with 4 nm bandwidth and a Purcell enhancement of $\sim$17. This cavity mode enables a directional far-field emission profile (88% overlap with a Gaussian) with a light extraction efficiency of $\sim$74%. Our solution opens up a route for generating entangled photon pairs with enhanced extraction efficiency and single-photon indistinguishability for the practical realization of quantum networks.
The spin of a charged semiconductor quantum dot (QD) coupled to an optical cavity is a promising candidate for high-fidelity spin-photon interfaces; the cavity selectively modifies the decay rates of optical transitions such that spin initialization, manipulation, and readout are all possible in a single magnetic field geometry. By performing cavity QED calculations, we show that a cavity with a single, linearly polarized mode can simultaneously support both high-fidelity optical spin initialization and readout in a single, in-plane (Voigt geometry) magnetic field. Furthermore, we demonstrate that single-mode cavities always outperform bimodal cavities in experimentally favorable driving regimes. Our analysis, when combined with established methods of control in a Voigt geometry field, provides optimal parameter regimes for high-fidelity initialization and readout, and coherent control in both cavity configurations, providing insights for the design and development of QD spin-photon interfaces as the basis of quantum network nodes and for the generation of photonic graph states. Published by the American Physical Society 2024