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Optics Communications

A local local oscillator passive continuous variable quantum key distribution scheme with trusted phase noise model and optical amplifiers

Xiaodong Wu, Duan Huang

Published Apr 5, 2025• 0 citations
Publisher
DOI
10.1016/j.optcom.2025.131796

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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.
We proposed a passive continuous-variable quantum key distribution (CVQKD) using a locally generated local oscillator (LLO) at reception. Different from the LLO-based Gaussian-modulated coherent-state quantum key distribution, our protocol is implemented by taking advantage of a multimode thermal source, beam splitters, optical attenuators, and homodyne detectors rather than the amplitude and phase modulators, which could be a cost-effective solution for LLO-based CVQKD. We adopt a general LLO noise model to analyze the performance of our protocol. That is to say, our consideration for noise in the proposed scheme contains the excess noise caused by passive state preparation, the phase noise, and the photon-leakage noise from the reference path. Because our protocol waives the necessity of the use of amplitude and phase modulators, there is no need to bear the effect of modulation noise caused by finite dynamics. Simulation results show that the improvement of the mode-overlap coefficient can suppress the excess noise caused by passive state preparation and thus enhance the performance of our protocol. Because lower relative phase drift and the photon-leakage noise can be obtained by using the multiplexing technique, we can still achieve reasonable performance of our protocol with the mode-overlap coefficient values which are very close to the experimental reference. Furthermore, we perform the finite-size analysis for the proposed protocol, which is more practical than that achieved in the asymptotic limit. This work confirms the feasibility of passive CVQKD implemented in the LLO configuration within the metropolitan area.
We study the validity of partially trusting the phase noise associated with estimation uncertainty in a continuous variable quantum key distribution system with a local local oscillator (LLO-CVQKD) and investigate optimal system parameters. We find that the trusted phase noise model enhances the key rate and transmission distance performance but opens a security loophole by manipulating the reference pulse amplitude. Therefore, we propose a “reference pulse attack” on the trusted phase noise LLO-CVQKD system where Eve achieves 100% information hacking without being detected at 23.8km and 32.0km while using lossless and 0.14dB/km loss channels, respectively. Nevertheless, by re-analyzing the attack, countermeasures are also proposed to keep the performance advantages of the trusted phase noise model. As a result, the trusted phase noise LLO-CVQKD can still provide a superior secure key rate (e.g., 9 times higher key rate at 20km) and an increased transmission distance by 45%, compared to that of the untrusted phase noise system.