Wireless quantum networking can provide flexible, rapidly deployable, and secure connectivity for mobile and infrastructure-limited scenarios. However, existing free-space continuous-variable quantum key distribution (CV-QKD) systems are still limited to point-to-point links, while dynamic multi-user access is hindered by bulky and slow mechanical beam steering. In this paper, we propose a free-space multi-user CV-QKD scheme based on an optical phased array. Based on a full-link model accounting for device imperfections and channel effects, numerical results demonstrate the feasibility of the proposed scheme under different atmospheric conditions and suggest its robustness and scalability. This work provides a promising route to rapidly reconfigurable free-space quantum access networks for highly dynamic near-range scenarios such as unmanned aerial vehicle swarms and emergency communications, and may inform future extensions toward satellite-based quantum networking.
Wireless quantum networking can provide flexible, rapidly deployable, and secure connectivity for mobile and infrastructure-limited scenarios. However, existing free-space continuous-variable quantum key distribution (CV-QKD) systems are still limited to point-to-point links, while dynamic multi-user access is hindered by bulky and slow mechanical beam steering. In this paper, we propose a free-space multi-user CV-QKD scheme based on an optical phased array. Based on a full-link model accounting for device imperfections and channel effects, numerical results demonstrate the feasibility of the proposed scheme under different atmospheric conditions and suggest its robustness and scalability. This work provides a promising route to rapidly reconfigurable free-space quantum access networks for highly dynamic near-range scenarios such as unmanned aerial vehicle swarms and emergency communications, and may inform future extensions toward satellite-based quantum networking.
Quantum key distribution (QKD) networks are crucial for the development of quantum networks and the early stages of the quantum internet, enabling unconditional secure key distribution and guaranteeing data security. However, current QKD networks are still limited in their structure, and are hard to achieve super multi-user access due to high system costs associated with the original point-to-point QKD system. In this paper, we introduce two cost-effective continuous-variable QKD (CV-QKD) access network schemes. The first one is a round-trip multi-band CV-QKD access network. Specifically, the frequency division multiplexing (FDM) technology is used to support multi-user access, and the round-trip optical architecture is adopted to realize low cost. As a result of the encoding properties of CV-QKD, different users can utilize the quadrature components in various frequency bands to transmit key information. The proposed network theoretically supports hundreds of users and can be easily expanded using simple equipment. The second one is a CV-QKD access network based on directed detection. With the help of the Kramers-Kronig relation, the receiver at the optical network unit can obtain the quadrature components just using a photodetector. Besides, it can also solve the practical issues in the plug-and-play structure. Compared with a quantum access network based on the point-to-point QKD system, these two schemes can provide cost-effective solutions for the subsequent large-scale verification and implementation of quantum access 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.
In recent years, continuous-variable quantum key distribution (CV-QKD) has become a promising paradigm for enabling secure communication among multiple end users sharing the same telecommunication backbone. CV-QKD with reverse reconciliation naturally enables scalability from conventional point-to-point links to quantum access networks based on passive quantum broadcasting channels. Here, we report an experimental demonstration on an active 1:4 multi-user CV quantum network (QN) in the finite-size regime. With 1.25⋅109 coherent states exchanged on each 11km quantum channel, the highest performance for secret key generation totaling 1.9⋅10−1 bits/channel use. Furthermore, we investigate adaptable CV-QN protocols that comprehensively allow network operation in various security and key rates requirements of individual users. The results establish the practical security of CV-QN compatible with existing telecommunication for broad deployment, and allowing additional degree of freedom for connected end users in existing infrastructures.
Future optical networks, envisioning the support of 6G services and related demanding requirements, should provide ultra-high-capacity and reliable connectivity, ensuring sustainability and security. Quantum key distribution (QKD) is a technology to address the limitations of classical cryptography, enabling quantum secure communications. Continuous variable QKD (CV-QKD) offers potential cost savings and enhanced compatibility with classical systems. This facilitates the integration within the network infrastructure, particularly in synergy with software-defined networking (SDN), further promoting interoperability and resource sharing/saving. For the adoption and practical implementation of CV-QKD, it is relevant to consider composable security and a finite number of symbols employed in the protocol (block size). In this work, we present the comparison of two models, to provide a figure of the required block size. We also assess the results using a simulation software. Furthermore, we explore a coexistence scenario considering a flexible grid, to exploit the CV-QKD capability of arbitrarily tuning the operating wavelength. This is a relevant feature enabling flexible allocation of the quantum channel to mitigate impairment and saving spectral resources. Considering realistic parameters aligned to commercially available CV-QKD systems and finite block size, we show an improvement with respect to our previous results. A minimum quantum-classical channel spacing of 112.5 GHz is required in a coexistence scenario with 8×200G transceivers and 9 dBm of total power over a 15 km link. In case of 10 dBm of total power, 125 GHz quantum-classical channel spacing is required to generate keys for practical implementation over the analyzed links. Finally, we discuss SDN aspects relevant for dynamic quantum channel allocation and flexible network management, enabling coexistence and efficient resource sharing, facilitating QKD technology integration in deployed networks. The presented results and envisioned potentialities of CV-QKD for practical implementation in optical networks pave the way for its adoption in the network infrastructure toward future quantum secure communications.
Free-space quantum key distribution opens up new possibilities for the development of quantum communication systems, facilitating the deployment of quantum networks in physically hard-to-reach areas and across wide landscapes without the use of optical fibers. This approach overcomes restrictions associated with cable laying and provides a more flexible infrastructure for quantum information transmission. Together with the use of continuous-variable protocols, it becomes possible to organize secure information transfer using optimal scalable communication systems despite deleterious environmental influences. This paper reviews key achievements and technical aspects of implementing continuous-variable quantum key distribution in atmospheric channels, considering the main atmospheric effects such as turbulence, scattering, and beam wandering. We present the current state of continuous-variable quantum key distribution systems in free space and their practical implementations, including successful experimental projects and prototypes. Prospects for further development, including integration with existing telecommunications networks and potential application areas, are discussed.
Free-space quantum key distribution (QKD) is expected to realized a global system for QKD based on a network of ground to satellite or satellite to satellite, and thus to extend the distance limit and the utility of QKD method (Schmitt-Manderbach et al., 2007). We report an experimental demonstration of free-space continuous-variable QKD (CV-QKD). We use a 1.55 m-wavelength pulsed diode laser and a pulsed homodyne detector. We have demonstrated free-space CV-QKD using a novel collinear interferometer. Our result shows the feasibility of practical free-space CV-QKD. We believe it will be an important step for the future study of free-space CV-QKD.