Violation of Bell inequalities by photons more than 10 km apart
arXiv:quant-ph/9806043 · doi:10.1103/PhysRevLett.81.3563
Abstract
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 2-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 competitor to the schemes based on weak pulses.
4 pages, REVTeX, 2 postscript figures included