Nonlinear metasurfaces have been demonstrated as ultrathin photon-pair sources, bringing resonant nanophotonics into a field traditionally dominated by bulk crystals and waveguides. Early experiments established spontaneous parametric down-conversion from nanoantennas and metasurfaces and showed resonant enhancement. Recent experiments and theoretical proposals address a more specific objective: a metasurface that emits the biphoton state required by a particular quantum-optical experiment. Resonant dispersion, mode symmetry, quasi-bound states in the continuum, guided-mode resonances, flatband design, multi-resonance interference, polarisation engineering and tunable emission geometry can shape both the pair-generation probability and the spatial, spectral and polarisation structure of the emitted state. This Perspective examines how these physical parameters determine the joint amplitude and which measurements establish the resulting two-photon state.
- Open Access
- Perspective
Beyond Brightness: Biphoton-State Engineering with Nonlinear Metasurfaces
Author Information
Received: 08 Jul 2026 | Revised: 21 Aug 2026 | Accepted: 24 Aug 2026 | Published: 01 Sep 2026
Abstract
Graphical Abstract
Keywords
nonlinear metasurfaces | spontaneous parametric down-conversion | biphoton state | quantum light | spatial entanglement | quantum imaging
References
- 1.
Solntsev, A.S.; Agarwal, G.S.; Kivshar, Y.S. Metasurfaces for Quantum Photonics. Nat. Photonics 2021, 15, 327–336. https://doi.org/10.1038/s41566-021-00793-z; Correction in Nat. Photonics 2021, 15, 862. https://doi.org/10.1038/s41566-021-00844-5.
- 2.
Poddubny, A.N.; Neshev, D.N.; Sukhorukov, A.A. Quantum Nonlinear Metasurfaces. In Nonlinear Meta-Optics; De Angelis, C., Leo, G., Neshev, D.N., Eds.; CRC Press: Boca Raton, FL, USA, 2020; Volume 1, pp. 147–180. https://doi.org/10.1201/b22515.
- 3.
Ma, J.; Zhang, J.; Horder, J.; et al. Engineering Quantum Light Sources with Flat Optics. Adv. Mater. 2024, 36, 2313589. https://doi.org/10.1002/adma.202313589.
- 4.
Zhang, J.; Kivshar, Y. Quantum Metaphotonics: Recent Advances and Perspective. APL Quantum 2024, 1, 020902. https://doi.org/10.1063/5.0201107.
- 5.
Wang, J.T.; Panoiu, N.C. Nonlinear Optical Metasurfaces Empowered by Bound-States in the Continuum. Rev. Phys. 2025, 13, 100117. https://doi.org/10.1016/j.revip.2025.100117.
- 6.
Sharapova, P.R.; Kruk, S.S.; Solntsev, A.S. Nonlinear Dielectric Nanoresonators and Metasurfaces: Toward Efficient Generation of Entangled Photons. Laser Photonics Rev. 2023, 17, 2200408. https://doi.org/10.1002/lpor.202200408.
- 7.
Marino, G.; Solntsev, A.S.; Xu, L.; et al. Spontaneous Photon-Pair Generation from a Dielectric Nanoantenna. Optica 2019, 6, 1416–1422. https://doi.org/10.1364/optica.6.001416.
- 8.
Santiago-Cruz, T.; Fedotova, A.; Sultanov, V.; et al. Photon Pairs from Resonant Metasurfaces. Nano Lett. 2021, 21, 4423–4429. https://doi.org/10.1021/acs.nanolett.1c01125.
- 9.
Son, C.; Sultanov, V.; Santiago-Cruz, T.; et al. Photon Pairs Bi-Directionally Emitted from a Resonant Metasurface. Nanoscale 2023, 15, 2567–2572. https://doi.org/10.1039/d2nr05499j.
- 10.
Liscidini, M.; Sipe, J.E. Stimulated Emission Tomography. Phys. Rev. Lett. 2013, 111, 193602. https://doi.org/10.1103/PhysRevLett.111.193602.
- 11.
Rozema, L.A.; Wang, C.; Mahler, D.H.; et al. Characterizing an Entangled-Photon Source with Classical Detectors and Measurements. Optica 2015, 2, 430–433. https://doi.org/10.1364/optica.2.000430.
- 12.
Faruque, I.I.; Burridge, B.M.; Banic, M.; et al. Quantum-Referenced Spontaneous Emission Tomography. Quantum Sci. Technol. 2023, 8, 045024. https://doi.org/10.1088/2058-9565/acf47b.
- 13.
Parry, M.; Mazzanti, A.; Poddubny, A.N.; et al. Enhanced Generation of Nondegenerate Photon Pairs in Nonlinear Metasurfaces. Adv. Photonics 2021, 3, 055001. https://doi.org/10.1117/1.ap.3.5.055001.
- 14.
Mazzanti, A.; Parry, M.; Poddubny, A.N.; et al. Enhanced Generation of Angle Correlated Photon-Pairs in Nonlinear Metasurfaces. New J. Phys. 2022, 24, 035006. https://doi.org/10.1088/1367-2630/ac599e.
- 15.
Santiago-Cruz, T.; Gennaro, S.D.; Mitrofanov, O.; et al. Resonant Metasurfaces for Generating Complex Quantum States. Science 2022, 377, 991–995. https://doi.org/10.1126/science.abq8684.
- 16.
Noh, J.; Santiago-Cruz, T.; Sultanov, V.; et al. Quantum Pair Generation in Nonlinear Metasurfaces with Mixed and Pure Photon Polarizations. Nano Lett. 2024, 24, 15356–15362. https://doi.org/10.1021/acs.nanolett.4c04398.
- 17.
Noh, J.; Santiago-Cruz, T.; Doiron, C.F.; et al. Fano Interference of Photon Pairs from a Metasurface. Light Sci. Appl. 2025, 14, 371. https://doi.org/10.1038/s41377-025-01998-5.
- 18.
Zhang, J.; Ma, J.; Parry, M.; et al. Spatially Entangled Photon Pairs from Lithium Niobate Nonlocal Metasurfaces. Sci. Adv. 2022, 8, eabq4240. https://doi.org/10.1126/sciadv.abq4240.
- 19.
Zhang, J.; Ma, J.; Neshev, D.N.; et al. Photon Pair Generation from Lithium Niobate Metasurface with Tunable Spatial Entanglement [Invited]. Chin. Opt. Lett. 2023, 21, 010005. https://doi.org/10.1364/COL.21.010005.
- 20.
Ma, J.; Zhang, J.; Jiang, Y.; et al. Polarization Engineering of Entangled Photons from a Lithium Niobate Nonlinear Metasurface. Nano Lett. 2023, 23, 8091–8098. https://doi.org/10.1021/acs.nanolett.3c02055.
- 21.
Ma, J.; Fan, T.; Haggren, T.; et al. Nonlinearity Symmetry Breaking for Generating Tunable Quantum Entanglement in Semiconductor Metasurfaces. Sci. Adv. 2025, 11, eadu4133. https://doi.org/10.1126/sciadv.adu4133.
- 22.
Jia, W.; Saerens, G.; Talts, Ü.-L.; et al. Polarization-Entangled Bell State Generation from an Epsilon-near-Zero Metasurface. Sci. Adv. 2025, 11, eads3576. https://doi.org/10.1126/sciadv.ads3576.
- 23.
Weissflog, M.A.; Ma, J.; Zhang, J.; et al. Directionally Tunable Co- and Counterpropagating Photon Pairs from a Nonlinear Metasurface. Nanophotonics 2024, 13, 3563–3573. https://doi.org/10.1515/nanoph-2024-0122.
- 24.
Ma, J.; Ren, J.; Zhang, J.; et al. Quantum Imaging Using Spatially Entangled Photon Pairs from a Nonlinear Metasurface. eLight 2025, 5, 2. https://doi.org/10.1186/s43593-024-00080-8.
- 25.
Ren, J.; Ma, J.; Tanaka, K.; et al. Quantum Phase Gradient Imaging Using a Nonlocal Metasurface System. Optica 2026, 13, 920–929. https://doi.org/10.1364/optica.586554.
- 26.
Liu, T.; Qin, M.; Feng, S.; et al. Efficient Photon-Pair Generation Empowered by Dual Quasibound States in the Continuum. Phys. Rev. B 2024, 109, 155424. https://doi.org/10.1103/physrevb.109.155424.
- 27.
Fan, T.; Zhang, J.; Sukhorukov, A.A. Enhanced Tunable Photon-Pair Generation from a Nonlinear Metasurface with a Guided-Mode Cavity. Phys. Rev. A 2025, 111, 063519. https://doi.org/10.1103/p1wr-98wx.
- 28.
Jiang, Y.; Zhang, J.; Ma, J.; et al. Flatband Nonlinear Metasurface for Broad-Angle Photon-Pair Generation. APL Quantum 2025, 2, 026115. https://doi.org/10.1063/5.0247669.
- 29.
Mao, Y.; Hu, R.; Xiang, Y.; et al. Dispersion-Free Photon-Pair Generation Enabled by Tailored Multipolar Flatband Resonances from a Nonlinear Metasurface. Opt. Lett. 2026, 51, 3838–3841. https://doi.org/10.1364/ol.605823.
- 30.
Fan, T.; Tang, Y.; Lung, S.; et al. Enhanced Photon-Pair Generation from a van der Waals Metasurface. Nano Lett. 2025, 25, 11844–11851. https://doi.org/10.1021/acs.nanolett.5c02170.
- 31.
Karaman, O.C.; Li, H.; Dayi, E.N.; et al. Photo-Thermally Tunable Photon-Pair Generation in Dielectric Metasurfaces. ACS Nano 2026, 20, 4079–4087. https://doi.org/10.1021/acsnano.5c14740.
- 32.
Yao, J.; Wang, Z.; Fan, Y.; et al. Intensity-Asymmetric Wavefront Shaping in Nonlocal Meta-Lens. Nat. Commun. 2026, 17, 2039. https://doi.org/10.1038/s41467-026-68638-3.
- 33.
Kumela, A.G.; Lanteri, S.; Papoff, F.; et al. Advanced Multi-Objective Optimization of Nonlinear Metasurface Unlocks Quantum Light Generation. Adv. Opt. Mater. 2026, 14, e03793. https://doi.org/10.1002/adom.202503793.
- 34.
Bacaoco, M.Y.; Koshelev, K.; Solntsev, A.S. Third-Order Spontaneous Parametric Down Conversion in Dielectric Nonlinear Resonant Metasurfaces. ACS Photonics 2025, 12, 4397–4405. https://doi.org/10.1021/acsphotonics.5c00750.
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