Decoy states for quantum key distribution based on decoherence-free subspaces
Zhen−Qiang Yin, Yibo Zhao, Zheng-Wei Zhou, Zheng‐Fu Han, Guang‐Can Guo · Physical Review A · 2008
A quantum key distribution with decoherence-free subspaces has been proposed to overcome collective noise to the polarization modes of photons flying in quantum channels. Prototypes of this scheme have also been achieved with a parametric down-conversion source. However, the photon-number-splitting attack we propose will make practical implementations of this scheme insecure since the parametric down-conversion source may occasionally emit multiphoton pairs. We propose a decoy-state method to make these implementations immune to this attack. With this decoy-state method, both the security distance and key bit rate will be increased.