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Advanced Photonics

Experimental verification for the feasibility of satellite-to-ground continuous-variable quantum key distribution

Mingxuan Guo, Peng Huang, Bangde Zhu, Kuntuo Zhu, Tao Wang, Guihua Zeng

Published Jul 28, 2026• 0 citations
Publisher

Abstract

As a key branch of satellite-to-ground quantum key distribution, satellite-to-ground continuous-variable quantum key distribution (CVQKD) possesses distinctive characteristics including high channel capacity, low cost, strong suppression of background light noise, and capability of all-day operation. However, although several theoretical studies have demonstrated its feasibility, there has been no experimental verification of satellite-to-ground CVQKD to date. The feasibility of CVQKD under the 1200 km satellite-to-ground channel with 41 dB loss in the asymptotic limit of infinitely long keys is preliminarily verified through experiments. We successfully recover the raw key at the Bob site and demonstrate its correlation with the Gaussian modulation data under a 41 dB loss channel using a quantum coherent light source at the Alice site. This confirms the virtual-entanglement is successfully established between Alice and Bob in CVQKD under a 41 dB loss channel. We further show, through experiments and theoretical analysis, that the excess noise under a 41 dB loss satellite-to-ground CVQKD channel can be suppressed to guarantee a positive secret key rate. Our results demonstrate the feasibility of satellite-to-ground CVQKD and provide a new reference scheme for its practical deployment.

DOI
10.1117/1.ap.8.5.056001

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As a key branch of satellite-to-ground quantum key distribution, satellite-to-ground continuous-variable quantum key distribution (CVQKD) possesses distinctive characteristics including high channel capacity, low cost, strong suppression of background light noise, and capability of all-day operation. However, although several theoretical studies have demonstrated its feasibility, there has been no experimental verification of satellite-to-ground CVQKD to date. The feasibility of CVQKD under the 1200 km satellite-to-ground channel with 41 dB loss in the asymptotic limit of infinitely long keys is preliminarily verified through experiments. We successfully recover the raw key at the Bob site and demonstrate its correlation with the Gaussian modulation data under a 41 dB loss channel using a quantum coherent light source at the Alice site. This confirms the virtual-entanglement is successfully established between Alice and Bob in CVQKD under a 41 dB loss channel. We further show, through experiments and theoretical analysis, that the excess noise under a 41 dB loss satellite-to-ground CVQKD channel can be suppressed to guarantee a positive secret key rate. Our results demonstrate the feasibility of satellite-to-ground CVQKD and provide a new reference scheme for its practical deployment.
The Gaussian modulated continuous variable quantum key distribution (GM-CVQKD) protocol is known to maximise the mutual information between two parties during quantum key distribution (QKD). An alternative modulation scheme is the discrete modulated CVQKD (DM-CVQKD) protocol. In this paper, we perform a feasibility study for practical satellite-to-ground CVQKD with a focus on comparing existing GM-CVQKD and DM-CVQKD protocols with the application of the performance of recent reconciliation methods. We use a satellite-to-ground link model which takes into account geometric losses, scintillation, and scattering losses from the link distance, atmospheric turbulence, and atmospheric aerosols, respectively. In addition, recent multidimensional (MD) and multilevel coding and multistage decoding (MLC-MSD) reconciliation method models in combination with multiedge-type low-density parity-check (MET-LDPC) code models have been used to determine the reconciliation efficiency. Realistic parameters have been used for the calculation of the secret key rate (SKR) along with a comparison between MD and MLC-MSD reconciliation during satellite-to-ground GM-CVQKD, for the first time. The results show that GM-CVQKD outperforms DM-CVQKD. In addition, GM-CVQKD with MD reconciliation outperforms GM-CVQKD with MLC-MSD reconciliation in the finite size limit by producing positive SKRs at larger link distances and lower elevation angles.
Continuous-variable quantum key distribution (CVQKD) enables remote users to share high-rate and unconditionally secure secret keys while maintaining compatibility with classical optical communication networks and effective resistance against background noise. However, CVQKD experiments have been demonstrated only indoors or over short outdoor distances. Here, by developing channel-fluctuation-independent high-precision manipulation of continuous-variable quantum states, high-accuracy quantum signal acquisition and processing, and high-efficiency free-space acquisition, tracking, and pointing technology, we overcome the excess noise due to atmospheric effects especially in daylight without extra wavelength conversion and narrow-linewidth spectral filtering and demonstrate for the first time long-distance free-space quantum key distribution under the asymptotic condition over 7-km inland and 9.6-km maritime atmospheric channels with Gaussian-modulated coherent states. Given that the CVQKD system is naturally compatible with existing ground fiber telecommunication networks, it marks an essential step for realizing integrated air-ground quantum access networks with cross-domain applications.
Continuous variable quantum key distribution (CVQKD) uses the continuous quadratures of light to share a secret key between a transmitter and receiver. The presence of an eavesdropper can be detected by fundamental quantum mechanics. Compared to the more established discrete variable QKD, CVQKD uses more cost-effective homodyne detectors which are more compatible with current telecommunication technologies. In a future global quantum network, CVQKD could be used to ensure the secure exchange of information. In this work, the feasibility of a variety of CVQKD protocols in different channels that could be used to establish a global quantum network are studied. These are the Gaussian modulated and discrete modulated CVQKD protocols for satellite to optical ground station downlinks and uplinks for Earth-space connections, inter-satellite links for space connections, satellite to ship and underwater links for maritime connections, and fibre network links for terrestrial connections. Secret key distribution between continents and various regions is simulated while accounting for the different adverse effects associated with each link. The combination of these connections with routing and scheduling ensures inter-continental high-speed information exchange with unconditional security that is required to achieve the goal of a global quantum network.
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.
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.
The advent of quantum computers has significantly challenged the security of traditional cryptographic systems, prompting a surge in research on quantum key distribution (QKD). Among various QKD approaches, continuous-variable QKD (CVQKD) offers superior resilience against background noise. However, the local local oscillator (LLO) CVQKD scheme faces substantial physical limitations in scenarios with high channel attenuation, and the large attenuation CVQKD remains unrealized. Bottleneck challenges include ensuring stable low-noise transmission and accurately estimating parameters under fluctuating channel conditions. We propose a continuous-mode theoretical framework that provides an analytical method for time-varying quantum systems within a free-space channel. This framework can achieve high-fidelity LLO-CVQKD in free space without the need for complex, real-time frequency locking and transmittance calibration equipment. It can also enable free-space QKD under large attenuation and high repetition frequency. Through experimental validation, we first demonstrate high-rate secure quantum key distribution over high-loss free-space channels. Specifically, we achieve asymptotic key rates of 76.366 kbps and 403.896 kbps in 25 dB attenuation free-space channels without turbulence and 21.5 dB average attenuation free-space channels with turbulence, respectively. Additionally, we confirm the feasibility of experiments on mildly turbulent atmospheric channels spanning at least 10.5 km using current equipment. Our scheme provides direct insight into constructing an integrated air-ground quantum communication network.