Researchers generate entangled photons using only focused sunlight

In a study published in Optica, scientists from the University of Ottawa and the Max Planck Institute for the Science of Light reported that a glass-cone solar concentrator can focus diffuse sunlight onto a millimetre-scale crystal to generate entangled photon pairs. The setup, built by Hanieh Fattahi’s group, used a window-sized Fresnel lens and a thin optical fiber to deliver the light, achieving an entanglement fidelity of roughly 94 % and a measurable violation of Bell’s inequality over three days of outdoor testing.

Cheng Li, a co-lead who now works at Lawrence Berkeley National Laboratory, emphasized that eliminating the laser-to-light conversion step makes quantum technology more affordable and portable. Robert Boyd, the senior author, explained that the slight shortfall compared with laser-driven sources is attributable to distortions in the optical components, which can be improved with further engineering. The researchers aim to increase brightness and entanglement quality to create field-deployable devices, potentially enabling satellites to generate quantum encryption keys directly from sunlight.