# Violation of Bell Inequalities by Photons More Than 10 km Apart

@article{Tittel1998ViolationOB, title={Violation of Bell Inequalities by Photons More Than 10 km Apart}, author={Wolfgang Tittel and J. Brendel and Hugo Zbinden and Nicolas Gisin}, journal={Physical Review Letters}, year={1998}, volume={81}, pages={3563-3566} }

A Franson-type test of Bell inequalities by photons 10.9 km apart is presented. Energy-time entangled photon pairs are measured using two-channel analyzers, leading to a violation of the inequalities by 16 standard deviations without subtracting accidental coincidences. Subtracting them, a two-photon interference visibility of 95.5% is observed, demonstrating that distances up to 10 km have no significant effect on entanglement. This sets quantum cryptography with photon pairs as a practical…

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