Overview
- A team from the University of Ottawa and the Max Planck Institute reported in Optica that concentrated sunlight produced polarization-entangled photon pairs using spontaneous parametric down-conversion in a millimetre nonlinear crystal.
- The experiment used a window-sized Fresnel lens feeding an all-glass, cone-shaped solar concentrator and a hair-thin optical fiber to focus sunlight onto the tiny crystal and trigger the SPDC process.
- Outdoor tests carried out over three days produced states with about 94 percent fidelity to an ideal entangled state and showed correlations that violated Bell’s inequality, confirming genuine quantum entanglement.
- The demonstration is a proof of principle because photon brightness and entanglement quality lag top laser sources, and the team is now engineering better optics and delivery to raise count rates and reduce distortions.
- The result builds on prior work showing incoherent LEDs can produce polarization entanglement and points to practical effects such as lower-power satellite quantum key generation and reduced energy needs for scaling quantum networks.