In the continuous variable measurement-device-independent quantum key distribution (CV-MDI-QKD) protocol, both Alice and Bob send quantum states to an untrusted third party, Charlie, for detection through the quantum channel. In this paper, we mainly study the performance of the CV-MDI-QKD system using the noiseless linear amplifier (NLA). The NLA is added to the output of the detector at Charlie’s side. The research results show that NLA can increase the communication distance and secret key rate of the CV-MDI-QKD protocol. Moreover, we find that the more powerful the improvement of the performance with the longer gain of NLA and the optimum gain is given under different conditions.

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.

In this paper, we propose a new scheme to enhance the performance of the Gussian-modulated coherent state(GMCS) continuous-variable measurement-device-independent quantum key distribution(CV-MDI-QKD) system via quantum scissors(QS) operation at Bob’s side. As an non-deterministic amplifying setup, we firstly introduce the QS-enhanced CV-MDI-QKD protocol and then investigate the success probability of the QS operation in accordance with the equivalent one-way scheme. Afterwards, we investigate the effect of the QS operation on the proposed scheme and analyze the performance of the QS-enhanced CV-MDI-QKD system under the extreme asymmetric circumstance. Simulation results show that the QS operation can indeed improve the performance of the CV-MDI-QKD system considerably. QS-enhanced CV-MDI-QKD protocol outperforms the original CV-MDI-QKD protocol in both the maximum transmission distance and the secret key rate. Moreover, the better the performance of QS operation, the more significant improvement of the performance of the system.