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Optics Continuum

Satellite continuous-variable quantum key distribution systems using code-division multiple access

Hang T. T. Phan, Minh B. Vu, Hien T. T. Pham, Ngoc The Dang

Published Jan 11, 2023• 2 citations
Publisher

Abstract

In this paper, we propose a novel architecture of the satellite continuous-variable quantum key distribution (CV-QKD) system that can not only support multiple users but also enhance the security. The satellite CV-QKD system is based on a code-division multiple access (CDMA) technique to simultaneously transmit multiple key streams from a trusted satellite to a ground station, which passively forwards these key streams to multiple users nearby via optical fibers. Our proposed architecture avoids using multiple ground stations that result in high costs. We analyze the performance of the proposed system under the negative impacts of atmospheric attenuation and atmospheric turbulence, as well as beam spreading and pointing error loss. Especially, the impact of multiple user interference is also considered in our analysis. The numerical results show that the proposed QKD system using CDMA can support multiple users, whose performance metrics such as quantum bit-error rate (QBER), sifted probability, and secret key rate meet the designed targets. The eavesdroppers suffer high QBER and low sifted probability, thus the security is guaranteed.

DOI
10.1364/optcon.474509

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In this paper, we propose a novel architecture of the satellite continuous-variable quantum key distribution (CV-QKD) system that can not only support multiple users but also enhance the security. The satellite CV-QKD system is based on a code-division multiple access (CDMA) technique to simultaneously transmit multiple key streams from a trusted satellite to a ground station, which passively forwards these key streams to multiple users nearby via optical fibers. Our proposed architecture avoids using multiple ground stations that result in high costs. We analyze the performance of the proposed system under the negative impacts of atmospheric attenuation and atmospheric turbulence, as well as beam spreading and pointing error loss. Especially, the impact of multiple user interference is also considered in our analysis. The numerical results show that the proposed QKD system using CDMA can support multiple users, whose performance metrics such as quantum bit-error rate (QBER), sifted probability, and secret key rate meet the designed targets. The eavesdroppers suffer high QBER and low sifted probability, thus the security is guaranteed.
In this paper, we propose a quantum code division multiple access (q-CDMA) based continuous-variable quantum key distribution (CV-QKD) system. In the proposed system, the quantum states of two senders (Alice1,2) are chaotically encoded through chaotic phase shifters and then transmitted over a quantum channel. At the receiver, the quantum states are decoded via chaos synchronization to separate the quantum states sent by the different senders and received by the two receivers (Bob1,2) separately. We characterize the input-output relation of the quadrature between the two senders and receivers and then analyze the secret key rate (SKR) of the q-CDMA-based CV-QKD system. Our numerical results reveal that the q-CDMA approach can significantly enhance the SKR for both users when compared to the single-user case without the q-CDMA approach.
This paper proposes the design of a global-scale free-space optics/quantum key distribution (FSO/QKD) network based on a geosynchronous (GEO) satellite as the secret key source and low-Earth orbit (LEO) satellites as relay nodes for multiple legitimate users on the ground. The continuous variable QKD (CV-QKD) protocol with dual-threshold/direct detection (DT/DD) receivers is employed. The system performance is analyzed by considering the spreading loss, atmospheric attenuation, and turbulence. Based on the design criteria for the proposed system, we investigate the feasibility of a case study for the Japan QKD network considering the unauthorized receiver attack (URA) and beam-splitting attack (BSA). In addition, we analyze the secret-key rate performance of the proposed system and perform Monte Carlo simulations to verify analytical results.
We present a quantum code-division multiple-access (q-CDMA) framework for multiuser continuous-variable quantum key distribution (CV-QKD) over a shared quantum channel. The proposed architecture employs chaotic phase shifters to encode and decode quantum states, enabling efficient multiplexing and demultiplexing of signals generated by multiple transmitters. In this scheme, quantum states from different users are chaotically phase-encoded and combined through a beam splitter network before transmission. At the receiver, synchronized chaotic phase shifters are used for decoding, followed by an inverse beam splitter structure to recover the individual user signals. This chaotic synchronization allows reliable state recovery and secure key establishment between each sender-receiver pair. For an arbitrary number of users, we derive the input-output quadrature relations describing the multiuser q-CDMA CV-QKD system. Using this model, we evaluate the achievable secret key rate under collective attacks with reverse reconciliation. We further investigate the impact of key system parameters including the correction factor, multiuser interference noise, environmental noise, and channel transmittance. A comparison between the asymptotic and finite-size regimes is also presented to highlight the associated performance trade-offs. These results provide a theoretical framework for assessing the performance of q-CDMA-based CV-QKD and support the development of scalable and secure multiuser quantum communication networks.
Abstract Driven by the necessitates of wide-area quantum secure communication networks, ground-to-satellite quantum key distribution (QKD) has been highlighted in the field of quantum information. Continuous variable QKD (CV-QKD) shows the advantages of a high secure key rate generation and compatibility in the fiber channel, but the communication range is limited by low attenuation tolerance. In this study, the feasibility of the uplink CV-QKD for Very Low Earth Orbit satellite is studied, and the influence of practical factors such as atmospheric turbulence and beam pointing errors under dynamic time-varying satellite orbital parameters is analyzed to model realistic transmission channels. A parameter optimization scheme for orbital parameters, spot size, receiving telescope aperture, and modulation variance has been proposed to enhance the performance of the actual uplink CV-QKD, providing a reference for parameter selection in CV-QKD experiments.
Satellite-based Quantum Key Distribution (QKD) is emerging as a cornerstone technology for secure global communication networks, extending quantum-safe key exchange beyond the limitations of terrestrial fiber systems. Achieving scalable and robust space-to-ground QKD links requires careful optimization of optical terminals, channel conditions, and protocol-specific parameters.In this work, we present a system-level analysis of design priorities for satellite QKD networks, using realistic atmospheric conditions modeled with MODTRAN 6 and a simulation tool designed and developed in-house. For discrete-variable (DV) QKD, we analyze how the secret key rate (SKR) varies with satellite altitude for two telescope aperture sizes under representative rural and urban ground station scenarios. Results show that DV-QKD enables secure key distribution over distances compatible with LEO and MEO satellite links when using moderately sized ground telescopes (600mm and 800mm apertures). For continuous-variable (CV) QKD with Gaussian modulation, SKR is analyzed as a function of satellite altitude under the most favorable link conditions identified in the DV-QKD study (800 mm ground aperture and rural environment), indicating that CV-QKD is feasible for secure key exchange with low-altitude LEO satellites, as long as the excess noise remains within low (yet experimentally achievable) levels (≈ 0.045 SNR). Additionally, we establish upper bounds on tolerable excess noise via heatmap analysis, defining the operational regime for secure CV-QKD.These findings provide quantitative guidance for designing scalable, interoperable, and cost-efficient space-to-ground QKD infrastructures, supporting the development of robust global quantum communication networks.
Continuous variable quantum key distribution (CV-QKD) has emerged as a promising candidate for quantum-secure communication due to its experimentally demonstrated high key rates in fiber-optic channels. However, the feasibility of discrete modulation CV-QKD in satellite-to-ground downlinks remains an open question due to practical challenges such as high transmission loss, limited communication windows, and atmospheric turbulence. In this work, a comprehensive framework is proposed to evaluate the feasibility of discrete modulation CV-QKD by integrating orbital dynamics and atmospheric channel models, and to comprehensively analyze the influence of the parameter space on free-space discrete modulation CV-QKD. To achieve this, a free-space CV-QKD simulation platform is employed, which calculates the elevation angle and transmission distance based on precise orbital models, thereby providing a more practical assessment of the key rate for discrete modulation CV-QKD. Simulation results verify the feasibility and practicality of discrete modulation CV-QKD in satellite-based quantum communication systems. Furthermore, the critical factors influencing the key rate performance are identified, and parameter optimization strategies are proposed, providing theoretical support for realizing the future satellite-to-ground discrete modulation CV-QKD.