Long-distance distribution of time-bin entanglement generated in a cooled fiber

This paper reports the first demonstration of the generation and distribution of time-bin entangled photon pairs in the 1.5-microm band using spontaneous four-wave mixing in a cooled fiber. Noise photons induced by spontaneous Raman scattering were suppressed by cooling a dispersion shifted fiber with liquid nitrogen, which resulted in a significant improvement in the visibility of two-photon interference. By using this scheme, time-bin entangled qubits were successfully distributed over 60 km of optical fiber with a visibility of 76%, which was obtained without removing accidental coincidences.