Long-range distribution of high-quality time-bin entangled photons for quantum communication

Entanglement is an essential ingredient in current experimental implementations for quantum communication. Nevertheless, distributing the entangled states to distant users, in high quality, via widely installed fiber channels has been a daunting problem. Here, we report an experimental distribution of high-quality entangled qubits over long-distance fiber channels, especially by using time-bin mode due to its outstanding robustness in fiber-optic distributions. In particular, by employing actively operating feedback schemes, we clearly demonstrate that the time-bin entanglement can be reliably shared between two distant parties, each separated by up to 60 km in all fiber-based implementations; then, we prove the significance of our study in long-range, long-lasting quantum communication by showing a high value of two-photon interference visibilities and a violation of the Clauser–Horne–Shimony–Holt Bell inequality.