"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].
Yeah that's the thing, quantum key distribution can not prove who is on the other end!
It fundamentally can not guarantee that the line is intact before you start communicating. You can in theory detect a break that starts after, but one that happened before is effectively invisible.
Quantum key distribution can not do anything other than key expansion (giving you more secret bits from a few), because the only way to know who is in the other end is to have agreed to a method of validation, such as a signature algorithm (but if you trust signatures you won't care about quantum key distribution) or a shared secret (an authentication tag key). But if you have a large enough secret key, you can just use a regular symmetric encryption algorithm. Some might want forward secrecy from the quantum line, but you can get that with symmetric key ratchets like Signal uses where the ONLY benefit of quantum key distribution is that you avoid key management (but instead you maintain physical infrastructure)