Researchers have demonstrated that sunlight can directly generate quantum entanglement between photons. For decades, lasers were considered the only viable method due to their high coherence. This breakthrough challenges that paradigm: the team used a cone-shaped solar concentrator to focus sunlight onto a nonlinear crystal, enabling spontaneous parametric down-conversion (SPDC) — a process where photons split into entangled pairs. The resulting entanglement showed about 94% fidelity to a perfect state and violated Bell’s inequality, confirming its non-classical nature. This approach could make quantum technologies more energy-efficient, particularly for satellites that would use abundant sunlight instead of power-hungry onboard lasers for secure encryption or quantum sensing.
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