Long-distance entanglement swapping with photons from separated sources

We report the experimental realization of entanglement swapping over long distances in optical fibers. Two photons separated by more than 2 km of optical fibers are entangled, although they never directly interacted. We use two pairs of time-bin entangled qubits created in spatially separated sources and carried by photons at telecommunication wavelengths. A partial Bell-state measurement is performed with one photon from each pair, which projects the two remaining photons, formerly independent onto an entangled state. A visibility high enough to infer a violation of a Bell inequality is reported, after both photons have each traveled through 1.1 km of optical fiber.