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arXiv:2104.11152 · PRX Quantum

Homodyne Detection Quadrature Phase Shift Keying Continuous-Variable Quantum key Distribution with High Excess Noise Tolerance

Wen‐Bo Liu, Chen-Long Li, Yuan-Mei Xie, Chen-Xun Weng, Jie Gu, Xiaoyu Cao, Yu-Shuo Lu, Bing-Hong Li, Hua‐Lei Yin, Zeng‐Bing Chen

Published Nov 12, 2021• 105 citations
arXivHTMLPDF

Abstract

Discrete-modulated continuous-variable quantum key distribution with homodyne detection is widely recognized for its ease of implementation, efficiency with respect to error correction, and its compatibility with modern optical communication devices.However, recent studies report that the application of homodyne detection obtains poor tolerance to excess noise and insufficient transmission distance, hence seriously restricting the large-scale deployment of quantum secure communication networks.In this paper, we propose a homodyne detection protocol using the quadrature phase shift keying technique.By limiting information leakage, our proposed protocol enhances excess noise tolerance to a high level.Furthermore, we demonstrate that homodyne detection performs better than heterodyne detection in quaternary-modulated continuous-variable quantum key distribution under the untrusted detector noise scenario.The security is analyzed using the tight numerical method against collective attacks in the asymptotic regime.Our results imply that the current protocol can distribute keys in nearly intercity area and, thus, paves the way for constructing low-cost quantum secure communication networks.

DOI
10.1103/prxquantum.2.040334

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Continuous-variable quantum key distribution with coherent detection is widely acknowledged for its compatibility with contemporary optical communication technologies. However, the robustness of various modulation formats and detection procedures against high excess noise remains uncertain, posing a significant barrier to the widespread implementation of quantum key distribution networks. This paper introduces a Matlab and Simulink-based experimental simulator designed to analyze different modulation formats (Gaussian and discrete) and coherent detection techniques (homodyne, heterodyne, and intradyne). Our findings suggest that polarization-multiplexed quantum signals with discrete modulation and pilot tones exhibit greater resilience to experimental imperfections. Enhanced robustness can be achieved through post-selection. Furthermore, under conditions of trusted detector noise, intradyne detection proves more effective in mitigating various offsets between the two nodes, thereby resulting in an increased secret key rate. The secure key rate is determined using the Gaussian extremity theorem for Gaussian modulation and a strict numerical technique against collective attacks in the asymptotic regime for discrete modulation. The results demonstrate that the protocol enables key distribution over distances approaching intercity scales, thereby supporting the advancement of cost-effective quantum-secure communication networks.
Most continuous-variable quantum key distribution schemes are based on the Gaussian modulation of coherent states followed by continuous quadrature detection using homodyne detectors. In all previous schemes, the Gaussian modulation has been carried out in conjugate quadratures thus requiring two independent modulators for their implementations. Here, we propose and experimentally test a largely simplified scheme in which the Gaussian modulation is performed in a single quadrature. The scheme is shown to be asymptotically secure against collective attacks, and considers a specific attack using asymmetric preparation and excess noise. We find that this protocol is considerably more sensitive to noise than other CVQKD schemes, as a consequence of the simplified implementation. A single-quadrature modulation approach renders the need for a costly amplitude modulator unnecessary, and thus facilitates commercialization of continuous-variable quantum key distribution, provided that the low noise requirement can be achieved.
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We report a fiber-based four-state discrete modulation continuous variable quantum key distribution system based on homodyne detection. A secret key rate of 1kbit/s is achieved at a transmission distance of 30.2 km. Two factors that result in the excess noises of the quantum key distribution system are analyzed. The first is the relative phase dithering between the signal and local fields, and the second is the local field leakage into the signal field due to the scattering process that depolarizes the local field. It is found that the latter has a significant impact on the excess noise, which is the main limiting factor to the long-distance secure quantum transmission. Some protocols are also given to decrease the excess noise effectively.
Most continuous-variable quantum key distribution schemes are based on the Gaussian modulation of coherent states followed by continuous quadrature detection using homodyne detectors. In all previous schemes, the Gaussian modulation has been carried out in conjugate quadratures thus requiring two independent modulators for their implementations. Here, we propose and experimentally test a largely simplified scheme in which the Gaussian modulation is performed in a single quadrature. The scheme is shown to be asymptotically secure against collective attacks, and considers asymmetric preparation and excess noise. A single-quadrature modulation approach renders the need for a costly amplitude modulator unnecessary, and thus facilitates commercialization of continuous-variable quantum key distribution.