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Applied Optics and Photonics China (AOPC): Optoelectronics and Nanophotonics

An improved phase compensation noise model for the continuous-variable quantum key distribution with real local oscillators

Biao Huang, Siyang Chen, Yongmei Huang, Zhenming Peng

Published Nov 5, 2020• 0 citations
Publisher

Abstract

In the continuous-variable quantum key distribution with real local oscillators, the reference pulses transmitted in the insecure quantum channel results in phase compensation noises on the homodyne detection of quantum signals. Traditionally, the phase compensation noise is modelled as a zero-mean Gaussian distribution for simplicity. However, it is more likely to be the one with non-zero mean in the actual environment. In this paper, the phase compensation noise is considered to be with a non-zero mean, and then the secure bound is analyzed according to the imperfect phase compensation noise model. The actual transmittance and excess noise are compared between the evaluation values derived from the theoretical analysis and the estimation values calculated by training signals. Simulation results show that the security analysis is consistent with the practical implementation, and the secret key rate decreases with the increasing mean value and noise variance.

DOI
10.1117/12.2576012

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In the continuous-variable quantum key distribution with real local oscillators, the reference pulses transmitted in the insecure quantum channel results in phase compensation noises on the homodyne detection of quantum signals. Traditionally, the phase compensation noise is modelled as a zero-mean Gaussian distribution for simplicity. However, it is more likely to be the one with non-zero mean in the actual environment. In this paper, the phase compensation noise is considered to be with a non-zero mean, and then the secure bound is analyzed according to the imperfect phase compensation noise model. The actual transmittance and excess noise are compared between the evaluation values derived from the theoretical analysis and the estimation values calculated by training signals. Simulation results show that the security analysis is consistent with the practical implementation, and the secret key rate decreases with the increasing mean value and noise variance.
Continuous-variable quantum key distribution (CVQKD) with a real local oscillator (LO) is confronted with new security issues attributed to the reference pulses transmitted together with quantum signals over the insecure quantum channel. This paper proposes a method of phase attack on reference pulses of the CVQKD with real LOs. Under the phase attack, the phase drifts of reference pulses are manipulated by eavesdroppers so that the phase compensation error is increased. Consequently, the secret key rate is reduced because of the imperfect phase compensation for quantum signals. Based on the noise model of imperfect phase compensation, both the parameters of actual transmittance and actual excess noise are deduced from the phase compensation accuracy, and then they are compared with those estimated by training signals. The simulation results show that the secret key rate calculated from the theoretical parameters is consistent with the one estimated by training signals.
Continuous-variable quantum key distribution (CVQKD) with a real local oscillator (LO) is confronted with new security problems due to the reference pulses transmitted together with quantum signals over the insecure quantum channel. In this paper, we propose a method of phase attack on reference pulses of the CVQKD with real LOs. Under the phase attack, the phase drifts of reference pulses are manipulated by eavesdroppers, and then the phase compensation error is increased. Consequently, the secret key rate is reduced due to the imperfect phase compensation for quantum signals. Based on the noise model of imperfect phase compensation, the practical security of the CVQKD under phase attack is analyzed. Besides, we propose an effective method to detect the intensity of phase attack, in which the deviation of phase compensation error on quantum signals and that on reference signals are monitored in real time. The simulation results show that the security analysis is accurate and the method of phase attack detection is feasible.
Continuous-variable quantum key distribution (CVQKD) with the local local oscillator (LLO) is confronted with new security problems due to the reference pulses transmitted together with quantum signals over the insecure quantum channel. In this paper, we propose a method of phase attack on reference pulses of the LLO-CVQKD with time-multiplexing. Under this phase attack, the phase drifts of reference pulses are manipulated by eavesdroppers, and then the phase compensation error is increased. Consequently, the secret key rate is reduced due to the imperfect phase compensation for quantum signals. Based on the noise model of imperfect phase compensation, the practical security of LLO-CVQKD under phase attack is analyzed. The simulation results show that the practical security is reduced due to the phase attack, yet it is still tight when system parameters are estimated by training signals.
The value of residual phase noise, after phase compensation, is one of the key limitations of performance improvement for continuous-variable quantum key distribution using a local local oscillator (LLO CV-QKD) system, since it is the major excess noise. However, due to the nonideality of the realistic devices implemented in practice, for example, imperfect lasers, detectors, and unbalanced interferometers, the value of residual phase noise in the current system is still relatively large. Here, we develop a phase noise model to improve the phase noise tolerance of the LLO CV-QKD schemes. In our model, part of the phase-reference measurement noise associated with detection efficiency and electronic noise of Bob's detector as well as a real-time monitored phase-reference intensity at Bob's side is considered trusted because it can be locally calibrated by Bob. We show that using our phase noise model can significantly improve the secure key rate and transmission distance of the LLO CV-QKD system. We further conduct an experiment to substantiate the superiority of the phase noise model. Based on experimental data of a LLO CV-QKD system in the 25-km optical fiber channel, we demonstrate that the secure key rate under our phase noise model is approximately 40% higher than that under the conventional phase noise model.
In continuous-variable quantum key distribution system with a true local oscillator (LLO CV-QKD), part of the phase noise associated with the coherent detector and the phase-reference intensity can be considered as trusted because which can be locally calibrated at the receiver’s side. The trusted phase noise model can significantly improve the noise tolerance of the system since the phase noise is the major excess noise. However, the transmission of the phase-reference pulse through the insecure quantum channel in the LLO CV-QKD system may leave rooms for the eavesdropper to mount attacks. Here, we propose a practical and flexible phase-reference intensity attack scheme using a phaseinsensitive amplifier to amplify the intensity of the phase-reference pulse. In this case, the eavesdropper can compromise the security of the LLO CV-QKD system severely by lowering the trusted part of the phase noise to compensate her increased attack on the signal pulse while the total excess noise is unchanged. We simulate the secure key rate with respect to the transmission distance to show that precisely monitoring the instantaneous intensity of the phase-reference pulse in real time is of great importance to guarantee the security of the LLO CV-QKD system.
In order to ensure the security of the local oscillator (LO) in continuous variable quantum key distribution (CV-QKD), the LO in CV-QKD based on the local LO (LLO) scheme no longer passes through the quantum channel. For the LLO scheme using homodyne detection, two orthogonal quadratures of reference pulse can only be measured sequentially, which, as a result, each signal pulse should be accompanied by a pair of identical reference pulses. However, due to the phase shift between two adjacent pulses, it is difficult to prepare dual reference pulses with the same phase relative to the LO. In this paper, we propose an improved method to get around this difficulty, which is demonstrated experimentally for a transmitter and a receiver connected by a 50 km single mode fiber. The phase noise measured in the experiment is 2.0×10−3rad2, which is comparable to the recent experimental results using heterodyne detection. This method simplifies the preparation of phase reference pulses and removes the obstacles for the application of homodyne detection in the LLO scheme. In addition, this method can also be used for the compensation of quadrature imbalance in heterodyne detection, then the performance of heterodyne detection can be improved.