Scientists generate quantum entanglement from ordinary sunlight

Quantum entanglement has always needed lasers. Until now.

A team at the Max Planck Institute for the Science of Light built a glass solar concentrator that funnels ambient sunlight through a cone-shaped device into an optical fibre thinner than a human hair. The result: entangled photon pairs with 94% fidelity, nearly matching a purpose-built laser.

The study, published in Optica, challenges a foundational assumption in quantum technology. Lasers have been considered indispensable for preparing quantum states of light. This work shows that filtered, concentrated sunlight can do the same job.

The implications reach beyond the lab. Satellites already bathe in sunlight. If they could generate entanglement from that ambient light, they could produce quantum encryption keys without carrying power-hungry laser systems. That changes the economics of space-based quantum networks.

The fidelity gap between sunlight and laser sources is small enough that the researchers believe further engineering could close it entirely. A decade of expensive laser infrastructure may give way to something far simpler.