Violation of Bell Inequalities by Photons More Than 10 km Apart

W. Tittel, J. Brendel, H. Zbinden, N. Gisin
1998 Physical Review Letters  
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
more » ... as a practical competitor to the schemes based on weak pulses.
doi:10.1103/physrevlett.81.3563 fatcat:zb3r35lfgrenxgntdkhlehnhbu