Fast and Simple Qubit-Based Synchronization for Quantum Key Distribution

We propose Qubit4Sync, a synchronization method for quantum-key-distribution (QKD) setups, based on the same qubits exchanged during the protocol and without requiring additional hardware other than that necessary to prepare and measure the quantum states, in a similar fashion to the clock recovery used in classical communications. Our approach introduces a cross-correlation algorithm with low computational complexity for high channel losses. We test the robustness of our scheme in a real QKD implementation, and we believe it may find application in other quantum communication protocols.