Quantum catalysis-assisted attenuation for improving free-space continuous-variable quantum key distribution

Quantum key distribution (QKD) has reached a global scale by utilizing the powerful scheme in free space scenes with a more flexible transmission. Unfortunately, the practical applicability of free-space QKD is usually curtailed by the fact that the atmospheric turbulence unavoidably destructs the quality of the quantum signal, which limits its maximum transmission distance. Here we propose an attenuation scheme for the Gaussian modulated coherent state QKD, in which a quantum catalysis operation acts as a noiseless attenuation process to regulate the potentially deteriorated quantum signal, enabling the improvement of maximal transmission distance. Compared with the original protocol, the QC-assisted attenuation presents a promotion of maximum transmission distance. In particular, we find that the zero-photon catalysis-based protocol performs better than the QC-based one. Numerical analysis shows that the QC-assisted attenuation can reduce the amount of information obtained by eavesdroppers, whereas it has a relatively light impact on mutual information. It provides a promising solution towards tackling the atmospheric turbulence in practice.