Practical security analysis of continuous-variable quantum key distribution with unbalanced heterodyne detector

When developing practical continuous-variable quantum key distribution (CVQKD), detector is necessary at the receiver’s side.We investigate the practical security of the CVQKD system with unbalanced heterodyne detector.The result shows that unbalanced heterodyne detector introduces extra excess noise into system and decreases the lower bound of secret key rate without awareness of the legitimate communicators, which leaves loopholes for Eve to attack the system. In addition, we find that the secret key rate decreases more severely with the increase of the degree of imbalance and the excess noise induced by the imbalance is proportional to the intensity of local oscillator (LO) under the same degree of imbalance. Finally, the countermeasure is proposed to resist this kind of effects.