Sunlight Generates Entangled Photons

Researchers from the University of Ottawa and the Max Planck Institute for the Science of Light (MPL) demonstrated that quantum entanglement between photons can be generated directly from sunlight, offering a more energy-efficient alternative to laser-based methods. Published in Optica, the study used spontaneous parametric down-conversion (SPDC) with a solar concentrator developed by MPL to focus sunlight onto a nonlinear crystal. The resulting entangled photons showed 94% fidelity to a perfectly entangled state and violated Bell's inequality, confirming genuine quantum entanglement. This proof-of-principle could enable satellites to generate secure encryption keys using sunlight, reducing reliance on onboard lasers and supporting hardware. The team is working to improve brightness and entanglement quality for field deployment.