World's first experimental demonstration of entanglement swapping using sum-frequency generation (SFG) between single photons

https://www.eurekalert.org/news-releases/1104682

"high signal-to-noise ratio between single photons (previously extremely weak) made possible using high-speed entangled photon-pair sources, low-noise superconducting nanowire single-photon detectors, high-efficiency nonlinear optical crystal... high-fidelity entanglement swapping without destroying resulting entangled pair, by detecting photon generated via SFG... photonic quantum information processing circuits' miniaturization/ efficiency, device-independent quantum key distribution transmission distance extension"