Researchers Generate Quantum Entanglement Directly From Sunlight

A team led by recent University of Ottawa graduate Cheng Li (with Robert Boyd's group) and the Max Planck Institute for the Science of Light (Hanieh Fattahi's group) generated polarization-entangled photon pairs using concentrated sunlight instead of a laser pump. Sunlight collected over 1.4 square meters by a Fresnel lens and solar concentrator on a sun-tracking mount was focused into a nonlinear crystal via spontaneous parametric down-conversion, producing entangled photons with about 94% fidelity and correlations that violated Bell's inequality, confirming genuine entanglement despite the sunlight's spatial and temporal incoherence. The outdoor demonstration points toward simpler, lower-power quantum light sources for satellites and secure communications that would not depend on laser hardware.