Cross time-bin photonic entanglement for quantum key distribution

We report a fully fibered source emitting cross time-bin-entangled photons at 1540 nm from type-II spontaneous parametric down-conversion. Compared to standard time-bin-entanglement realizations, the preparation interferometer requires no phase stabilization, simplifying its implementation in quantum key distribution experiments. Bell-type tests of such a cross time-bin state are performed in the Franson configuration and lead to two-photon interference raw visibilities greater than 95$%$, which are only limited by the dark counts in the detectors and imperfections in the analysis system. Just by trusting the randomness of the beam splitters, the correlations generated by the source can be proved of nonclassical origin even in a passive implementation. The obtained results confirm the suitability of this source for time-bin-based quantum key distribution.