Scientists generate quantum entanglement from sunlight in Optica study

Researchers have generated quantum entanglement directly from sunlight, ScienceDaily reported, citing work published in Optica by teams at the University of Ottawa and the Max Planck Institute for the Science of Light. Cheng Li, a recent University of Ottawa graduate and first author, said the outdoor experiment produced entanglement comparable to laser-based methods when bandwidth differences are accounted for, with about 94% similarity to an ideal entangled state. The photons also showed correlations that violate Bell's inequality. The team used spontaneous parametric down-conversion with strongly polarized but spatially and temporally incoherent sunlight. An all-glass solar concentrator designed by Hanieh Fattahi's group funneled window-scale Fresnel-lens light into a hair-wide fiber onto a roughly millimeter-scale nonlinear crystal. Li said the approach could one day help satellites create encryption keys using sunlight already available in space and support more energy-efficient quantum computing. Earlier Boyd-group work had used LEDs; sunlight was a harder test because of its broad spectrum and many propagation directions. The citation is Cheng Li et al., Optica, 2026; 13 (8): 1508, DOI: 10.1364/OPTICA.601797.