biostudies-literatureUnknown631(8020)Sultanov VLiquid crystals, with their ability to self-assemble, strong response to an electric field and integrability into complex systems, are key materials in light-beam manipulation¹. The recently discovered ferroelectric nematic liquid crystals^2,3 also have considerable second-order optical nonlinearity, making them a potential material for nonlinear optics^4,5. Their use as sources of quantum light could considerably extend the boundaries of photonic quantum technologies⁶. However, spontaneous parametric down-conversion, the basic source of entangled photons⁷, heralded single photons⁸ and squeezed light⁹, has so far not been observed in liquid crystals-or in any liquids or organic materials. Here we implement spontaneoNature294-299https://www.ebi.ac.uk/biostudies/studies/S-EPMC11236711biostudies-literatureTunable entangled photon-pair generation in a liquid crystal.PMC11236711Sultanov VKokkinakis EChekhova MVKavcic ASebastian NHumar MfalseTunable entangled photon-pair generation in a liquid crystal.Liquid crystals, with their ability to self-assemble, strong response to an electric field and integrability into complex systems, are key materials in light-beam manipulation¹. The recently discovered ferroelectric nematic liquid crystals^2,3 also have considerable second-order optical nonlinearity, making them a potential material for nonlinear optics^4,5. Their use as sources of quantum light could considerably extend the boundaries of photonic quantum technologies⁶. However, spontaneous parametric down-conversion, the basic source of entangled photons⁷, heralded single photons⁸ and squeezed light⁹, has so far not been observed in liquid crystals-or in any liquids or organic materials. Here we implement spontaneo2024-01-01T00:00:00Z2024 Jul2025-04-05T15:49:05.357Z2025-04-05T15:49:05.357ZS-EPMC112367113886705410.1038/s41586-024-07543-5