An international group of researchers, including specialists from the University of Ottawa and the Max Planck Institute for Light Science in Germany, has published the results of a significant experiment in the journal Optica. Scientists have demonstrated that concentrated sunlight is capable of generating pairs of quantum entangled photons. This result calls into question the well–established notion that lasers have no alternative as a pumping source for spontaneous parametric downward scattering, a standard method for obtaining entangled states of light. Previously, laser installations were considered practically indispensable due to their high coherence and power density. However, a new study proves that the spatial and temporal incoherence of solar radiation is not a critical limitation for generating polarization entanglement, provided sufficient focusing and maintaining the polarization of the luminous flux.

To conduct the experiment, the scientific team developed and assembled a specialized sunlight concentration system with a collection area of 1.4 square meters. The solar flux was focused using a Fresnel lens, after which it was directed into a glass conical concentrator and a multimode optical fiber. At the final stage, the prepared light beam was fed into a nonlinear crystal, where the photon pair generation process took place. At the output, the researchers recorded the receipt of polarizationally entangled photons with an accuracy (state fidelity) of almost 94%. The obtained correlations reliably violated Bell's inequality, which is an indisputable experimental confirmation of genuine quantum entanglement achieved without the use of traditional coherent laser sources.

The authors stated that the normalized efficiency of entangled pair generation in this setup is comparable to that of classical laser systems. This breakthrough has significant practical implications for the development of photonic quantum technologies. The proposed approach has the potential to significantly reduce the energy consumption required for the functioning of quantum systems and simplify their deployment in conditions of severe energy scarcity. In particular, this technology is considered as a promising solution for equipping satellites and interplanetary space missions, where every watt of power is critical. Against this background, in July, leading organizations including AWS, Nvidia, Lawrence Berkeley National Laboratory and NASA also assessed the growing need for supercomputers to support and simulate complex quantum systems.