Loss Control-Based Key Distribution under Quantum Protection.

Quantum cryptography revolutionizes secure information transfer, providing defense against both quantum and classical computational attacks. The primary challenge in extending the reach of quantum communication comes from the exponential decay of signals over long distances. We meet this challenge by experimentally realizing the Quantum-Protected Control-Based Key Distribution (QCKD) protocol, utilizing physical control over signal losses. By ensuring significant non-orthogonality of the leaked quantum states, this control severely constrains eavesdroppers' capacities. We demonstrate the performance and scale of our protocol by experiments over a 1707 km long fiber line. The scalability of the QCKD opens the route for globally secure quantum-resistant communication.