Sunlight has been used for the first time to create quantum entanglement — a breakthrough in photonic technologies.
An international collaboration of physicists has made a significant step in the development of quantum technologies by demonstrating that concentrated sunlight can generate pairs of quantum-entangled photons. The results of this work, published in the reputable scientific journal Optica, open new horizons for creating energy-efficient quantum systems.
Lasers are no longer the only path
In the study, which brought together specialists from the University of Ottawa and the Max Planck Institute for the Science of Light, sunlight served as a pump source for spontaneous parametric down-conversion—a key method for producing entangled photon pairs. This experiment challenges the established notion that lasers are the only viable tool for preparing quantum states of light.
For a long time, it was believed that the high coherence and power density of laser radiation were indispensable for such tasks. However, my colleagues have proven the opposite: the spatial and temporal incoherence of sunlight is not a critical obstacle to generating polarization entanglement, provided that polarization is preserved and the flux is sufficiently focused.
Technical details of the experiment
To achieve the result, the team constructed a solar radiation concentration system with a collection area of 1.4 square meters. The light was focused by a Fresnel lens, passed through a glass conical concentrator and multimode optical fiber, and was then directed into a nonlinear crystal. At the output, the researchers recorded polarization-entangled photons with an accuracy of up to 94% and correlations that violate Bell's inequality—a convincing confirmation of the genuine quantum nature of the phenomenon.
Notably, the normalized generation efficiency proved comparable to laser-based setups. In my assessment, this discovery could radically change the approach to designing photonic quantum systems, especially under strict energy constraints.
Practical prospects
The development paves the way for reducing the energy consumption of quantum devices, which is critical for their application in satellite systems and interplanetary missions, where every watt of energy counts. This is especially relevant in light of recent assessments by leading technology corporations, including AWS and Nvidia, regarding the need for supercomputer infrastructure to support quantum computing.
My expert view: This achievement is not merely a laboratory curiosity but an important step toward the democratization of quantum technologies. Using a renewable light source instead of energy-intensive lasers could significantly reduce the cost and complexity of creating quantum communication networks. However, before commercial implementation, issues of scaling and stability of such systems in real-world operating conditions must be addressed.