Quantum key distribution with relay-assisted scheme over long atmospheric channels

A relay-assisted scheme for quantum key distribution (QKD) over long atmospheric channels is proposed. In this scheme, a polarization orbital-angular-moment with measurement-device-independent (POAM-MDI) QKD for quantum relay is designed to both reconstruct the turbulence-degraded qubits and redirect the qubits to the next relay or to Bob who performs detection randomization. The proposed scheme will neither be time-consuming nor lead to unstable or even intermittent in volatile environments. Theoretical and numerical results show that the proposed relay-assisted scheme outperforms the conventional direct transmission over long atmospheric channels.