"This technology could one day enable satellites to create secure encryption keys using the sunlight already abundant in space, reducing the need for onboard lasers and much of the supporting hardware," said Li, first author of the paper. "Sunlight-driven entanglement generation could also provide the crucial ingredient needed to scale up quantum computing without adding to the energy burden."

Scientists have traditionally believed that producing the strong correlations needed for photon entanglement requires coherent light. In coherent light, the waves remain synchronized so that their peaks and valleys follow a predictable pattern. Lasers are commonly used for this purpose because they generate highly coherent light concentrated at a single color.

https://en.wikipedia.org/wiki/Fresnel_lens

https://en.wikipedia.org/wiki/Catadioptric_system

link to open access article https://opg.optica.org/optica/fulltext.cfm?uri=optica-13-8-1508

Studies have proposed using solar concentration technology to directly drive optical amplification and build a solar laser [40–43]. On the other hand, large-scale solar-powered space infrastructure, such as space-based solar power platforms [44] and orbital data centers [45], is rapidly advancing, driving interest in photonic technologies capable of operating directly on abundant, incoherent solar radiation without dependence on power-intensive laser or electrical subsystems.

Within this landscape, solar-driven photonic quantum technologies represent a promising route toward energy-autonomous quantum photonic functionality, naturally aligned with the requirements of future space power and information architectures. Here, we demonstrate, for the first time, that sunlight, a ubiquitous and environmentally friendly light source, can produce entangled-photon pairs via SPDC despite its lack of optical coherence.

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These results are not simply a proof of principle that polarization entanglement is generated from SPDC pumped by sunlight; they are a quantitative demonstration that these photon pairs have entanglement close to that of many recent results on polarization entanglement generated from SPDC pumped by coherence laser sources [50–53].