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International Conference on 6G Communications and IoT Technologies (6GIoTT)

Reliable Synchronization Technology for Continuous Variable Quantum Key Distribution System

Huagui Li, Heliang Song, Xuchao Liu, Jiaxu Wen, Shilun Sun, Shaobo Li

Published Oct 1, 2022• 1 citation
Publisher

Abstract

Data synchronization is a critical technique for subsequent signal processing and secret key extraction of continuous variable quantum key distribution (CVQKD). In this paper, we propose a four-segment synchronization frame structure for CVQKD data synchronization at the first attempt. In order to verify the effectiveness of the structure, we build a data synchronization model containing device noise and fiber nonlinear noise. Simulation results indicate that the synchronization structure can effectively resist the influences of device electronic and fiber nonlinear noise, which is characterized by strong noise immunity, high reliability and easy implementation. The probability of bit synchronization and frame synchronization is 0.44 and 0.76 respectively when link distance is 50km.

DOI
10.1109/6giott57212.2022.00015

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Data synchronization is a critical technique for subsequent signal processing and secret key extraction of continuous variable quantum key distribution (CVQKD). In this paper, we propose a four-segment synchronization frame structure for CVQKD data synchronization at the first attempt. In order to verify the effectiveness of the structure, we build a data synchronization model containing device noise and fiber nonlinear noise. Simulation results indicate that the synchronization structure can effectively resist the influences of device electronic and fiber nonlinear noise, which is characterized by strong noise immunity, high reliability and easy implementation. The probability of bit synchronization and frame synchronization is 0.44 and 0.76 respectively when link distance is 50km.
In a practical continuous variable quantum key distribution (CVQKD) system, frame synchronization is crucial for its operation, especially in conditions of low signal-to-noise ratio (SNR) and phase drift. This paper introduces a robust frame synchronization scheme for CVQKD systems that only utilizes quantum signals. The proposed scheme effectively employs randomly selected segments of quantum signals to achieve frame synchronization, eliminating the need for additional modulation. The performance of this scheme applied in a local local oscillator scenario is thoroughly analyzed through numerical simulations. The results demonstrate that the proposed scheme is capable of withstanding low SNR and arbitrary slow phase drift, as well as fast phase drift originates from two independent lasers, while also slightly improving the secret key rate compared to the scheme using inserted synchronization frames. These findings validate the feasibility of implementing the proposed scheme for long-distance CVQKD in practical scenarios.
Considering a practical continuous variable quantum key distribution(CVQKD) system, synchronization is of significant importance as it is hardly possible to extract secret keys from unsynchronized strings. In this paper, we proposed a high performance frame synchronization method for CVQKD systems which is capable to operate under low signal-to-noise(SNR) ratios and is compatible with random phase shift induced by quantum channel. A practical implementation of this method with low complexity is presented and its performance is analysed. By adjusting the length of synchronization frame, this method can work well with large range of SNR values which paves the way for longer distance CVQKD.
In continuous-variable quantum key distribution (CVQKD) systems, high-quality data synchronization between two legitimate parties, Alice and Bob, is the premise of the generation of shared secret keys. Synchronization with specially designed frames is an efficient way, but it requires special modulating devices to generate these special frames. Moreover, the extra requirement of special modulating devices makes it technically impossible for some passive preparation schemes. We propose a novel approach to realize synchronization in this paper, which is different from those special-frame-based methods. In our proposed scheme, Alice publishes parts of the original signals as the synchronization frames and Bob takes these frames to perform the synchronization algorithm. Besides, a synchronization feature is applied to deal with phase shifts. The simulation results based on practical data demonstrate that the proposed synchronization scheme not only maintains a high success rate but simplifies the data processing flow at the same time, which dramatically reduces the computational complexity.
Abstract Frame synchronization is essential in continuous‐variable quantum key distribution (CVQKD), typically relying on active modulation to establish a specific frame structure. In passive CVQKD systems, however, the elimination of modulation requirements poses a significant challenge for frame synchronization, especially in local‐local‐oscillator (LLO) configurations. This paper introduces a robust, modulation‐free frame synchronization method tailored for passive LLO CVQKD systems. This method leverages the complex cross‐correlation of quantum signals exchanged between Alice and Bob for synchronization purposes. Validated through an analytical model and numerical simulations, this approach demonstrates high synchronization success rates, robustness to noise, and resilience to both slow phase drifts between local oscillators and quantum signals and fast phase drifts stemming from two independent lasers. These results underscore the viability of the proposed method for implementing long‐distance CVQKD in real‐world scenarios.
Summary form only given. Continuous-variable quantum key distribution (CVQKD) is a promising alternative to commonly used discrete-variable QKD protocols, because this technology can be implemented with standard telecom components and recent results suggest that it will be compatible with standard wavelength division multiplexed telecommunication networks [1]. Security proofs against general eavesdropping attacks are available for CVQKD protocols using Gaussian modulation [2], and field implementations over deployed telecommunication networks have been demonstrated over the past few years [3].Long-distance operation of CVQKD systems, however, has been hindered until now by the limited efficiency of the complex error-correction (or reconciliation) algorithms that are required to extract the secret key from the correlated data shared by Alice and Bob. We have designed high-efficiency error correcting-codes [4] allowing to extract an errorless secret key in a CVQKD protocol using a Gaussian modulation of coherent states and a homodyne detection system. These codes are available for a wide range of signal-to-noise ratios on a Gaussian noise channel with a binary modulation and can be combined with a multidimensional reconciliation method [5]. This improved reconciliation procedure considerably extends the secure range of a continuous-variable quantum key distribution with Gaussian modulation.
Clock synchronization is crucial for a practical continuous-variable quantum key distribution system to precisely get the measurement result. Three different synchronization schemes for continuous-variable quantum key distribution system are presented to demonstrate the optimal scheme. The performance of synchronization scheme is evaluated by measuring the excess noise which is the critical parameter for the continuous-variable quantum key distribution system. The experiment results show that distilling the synchronization signal from the local oscillator has the simplest physical implemention and superior effect of synchronization, but a stronger local oscillator is required. Transmitting synchronization signal and quantum signal in the same fiber by wave-length division multiplex is also a fine way to provide stable clock when we take no account of the phsical device and wave-length source.