Long-distance entanglement swapping with photons from separated sources

Abstract

We report the experimental realization of entanglement swapping over long distances in optical fibers. Two photons separated by more than $2\phantom{\rule{0.3em}{0ex}}\mathrm{km}$ 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 $1.1\phantom{\rule{0.3em}{0ex}}\mathrm{km}$ of optical fiber.