A sunlight-powered experiment produced entangled photon pairs with a quantum state about 94% similar to a perfectly entangled state, marking a proof of principle that natural light can replace lasers in this role.
Using spontaneous parametric down-conversion, the team focused polarized sunlight onto a nonlinear crystal with a window-sized Fresnel lens and a cone-shaped glass concentrator feeding an optical fiber.
Bell-inequality violations and quantum state tomography showed the correlations were genuinely quantum rather than classically reproducible, with performance comparable to laser-based setups after accounting for sunlight’s broader bandwidth.
The result targets a key bottleneck in quantum hardware—lasers need power, cooling and control systems—and suggests future satellites could generate secure quantum keys without carrying complex laser equipment.
The researchers said the source still needs better brightness, stability and entanglement quality before practical deployment, but the work broadens the range of light sources considered usable for quantum technologies.