Polychromatic resources have transformed classical communication networks by boosting rate and scalability; quantum communication networks are reaching a similar inflection point. Here, we report a polychromatic continuous-variable quantum communication network enabled by optical frequency combs. The multi-mode density matrices constituted by polychromatic quantum networks are studied. We incorporate finite mode isolation into the security analysis to bound Eve’s accessible information and compute the total network secret key rate. It is demonstrated that, compared to other multiplexing techniques, polychromatic quantum networks can theoretically achieve a secret key rate without decreasing with the increase in users. In the experiment, direct-transmission type and round-trip type quantum communication networks were built using optical frequency combs and dual-comb interference detection technology. The Gaussian-modulated continuous-variable quantum key distribution (CV-QKD) protocol has been validated, with a network capacity of 19 and a total secret key rate of 8.75 Gbps at a uniform distance of 5 km (asymptotic case), 0.82 Mbps at 120 km (finite-size effect), 89.10 Mbps at 40 km (composable security), 13.66 Mbps at 40 km (composable finite-size security). This implementation not only provides technical support for a high-speed multi-node quantum network, but also provides a solution for the future quantum Internet with continuous variables.
Polychromatic resources have transformed classical communication networks by boosting rate and scalability; quantum communication networks are reaching a similar inflection point. Here, we report a polychromatic continuous-variable quantum communication network enabled by optical frequency combs. The multi-mode density matrices constituted by polychromatic quantum networks are studied. We incorporate finite mode isolation into the security analysis to bound Eve’s accessible information and compute the total network secret key rate. It is demonstrated that, compared to other multiplexing techniques, polychromatic quantum networks can theoretically achieve a secret key rate without decreasing with the increase in users. In the experiment, direct-transmission type and round-trip type quantum communication networks were built using optical frequency combs and dual-comb interference detection technology. The Gaussian-modulated continuous-variable quantum key distribution (CV-QKD) protocol has been validated, with a network capacity of 19 and a total secret key rate of 8.75 Gbps at a uniform distance of 5 km (asymptotic case), 0.82 Mbps at 120 km (finite-size effect), 89.10 Mbps at 40 km (composable security), 13.66 Mbps at 40 km (composable finite-size security). This implementation not only provides technical support for a high-speed multi-node quantum network, but also provides a solution for the future quantum Internet with continuous variables.
In classical communication, the introduction of polychromatic resources has rapidly boosted classical networks' rate and scale. Quantum communication is now at a similar critical stage in its development, and therefore, it is essential to investigate polychromatic quantum communication networks. In this letter, we report a polychromatic continuous-variable quantum communication network enabled by optical frequency combs. The multi-mode density matrices constituted by polychromatic quantum networks are studied. Considering the limited mode isolation, the maximum amount of information that eavesdroppers can obtain is recalculated, therefore, the total secret key rate is provided. We have also demonstrated that, compared to other multiplexing techniques, polychromatic quantum networks can theoretically achieve a secret key rate without decreasing with the increase in users. In the experiment, direct-transmission type and round-trip type quantum communication networks were built using optical frequency combs and dual-comb interference detection technology. The Gaussian-modulated continuous-variable quantum key distribution (CV-QKD) protocol has been validated, with a network capacity of 19 and a total secret key rate of 8.75 Gbps at a uniform distance of 5 km (asymptotic case), 0.82 Mbps at 120 km (finite-size effect), 89.10 Mbps at 40 km (compsable security), 13.66 Mbps at 40 km (compsable finite-size security). This implementation not only provides technical support for a high-speed multi-node quantum network, but also provides a solution for the future quantum Internet with continuous variables.
Quantum key distribution (QKD), providing a way to generate secret keys with information-theoretic security, is arguably one of the most significant achievements in quantum information. The continuous-variable QKD (CV-QKD) offers the potential advantage of achieving a higher secret key rate (SKR) within a metro area, as well as being compatible with the mature telecom industry. However, the SKR and transmission distance of state-of-the-art CV-QKD systems are currently limited. Here, based on the proposed orthogonal-frequency-division-multiplexing (OFDM) CV-QKD protocol, we demonstrate a high-rate multi-carrier (MC) CV-QKD with a 10 GHz symbol rate that achieves Gbps SKR within 10 km and Mbps SKR over 100 km in the finite-size regime under composable security against collective attacks. The results are achieved by suitable optimization of subcarrier number and modulation variance, well-controlled excess noise induced by both the OFDM mechanism and the efficient DSP scheme, and high-performance post-processing capacity realized by the heterogeneous computing scheme. The composable finite-size SKR reaches 1779.45 Mbps@5 km, 1025.49 Mbps@10 km, 370.50 Mbps@25 km, 99.93 Mbps@50 km, 25.70 Mbps@75 km, and 2.25 Mbps@100 km, which improves the SKR by two orders of magnitude and quintuples the maximal transmission distance compared to the most recently reported CV-QKD results [ Nat. Commun. 13 , 4740 ( 2022 ) NCAOBW 2041-1723 10.1038/s41467-022-32161-y ]. Interestingly, it is experimentally verified that the SKR of the proposed MC CV-QKD can approach five times larger than that of the single-carrier CV-QKD with the same symbol rate without additional hardware costs. Our work constitutes a critical step toward future high-speed quantum metropolitan and access networks.
Abstract Quantum secret sharing (QSS), as a fundamental cryptographic protocol for future quantum networks, continues to face significant challenges, particularly in the generation of multipartite entanglement and the degradation of entanglement fidelity during distribution, both of which severely limit its scalability. These persistent constraints motivate an alternative approach based on continuous-variable (CV) systems. We propose a CVQSS scheme based on an electro-optically modulated optical frequency comb. The scheme employs a single laser to generate multi-wavelength coherent states, enabling the efficient and flexible construction of secret sharing subnetworks. By incorporating a broadcast-based distribution mechanism, the architecture is scalable to 128 players. Experimental verification with 24 players over a 10 km fiber link demonstrates a secret sharing rate of 6.24 per player under asymptotic conditions and 1.27 Mbps per player under finite-size effects, and a 1.05MB image is secretly shared to six players. This work achieves information-theoretically secure QSS both within and across subnetworks, providing a solid technical foundation for the development of scalable and multifunctional quantum networks.
Quantum key distribution (QKD) can theoretically accomplish unconditionally secure communication with the support of quantum mechanics. The point-to-point QKD system has already been well developed, and the focus of advanced research has shifted more toward QKD networks. However, it is still unclear how to achieve the maximum secret key rate within the limited physical bandwidth in QKD networks. In this paper, we propose an orthogonal frequency division multiplexing continuous-variable QKD access network (CV-QAN), which improves the bandwidth utilization efficiency to the Nyquist limit. Specifically, each quantum network unit prepares a carrier-modulated Gaussian-modulated coherent state so that they become orthogonal in the frequency domain when received by the quantum line terminal. Crosstalk arising from the multi-path effect among multi-mode quantum states was effectively suppressed through the implementation of a cyclic prefix. In this theory, we have demonstrated the feasibility of this scheme through the continuous-mode Gaussian information theory. In this experiment, we conducted a local local oscillator (LLO) CV-QAN experiment within the existing passive optical network architecture. The network capacity of CV-QAN is 7, and the secret key rate of each user reaches 4.06 and 0.87 Mbps at 25 km in the asymptotic case and the finite-size effect, respectively. This achievement has established an efficient and simple QAN based on digital signal processing, laying the foundation for the practicality and commercialization of large-scale quantum networks.
Establishing scalable, secure quantum networks requires advancing beyond conventional point-to-point quantum key distribution (QKD) protocols toward point-to-multipoint QKD protocols. Here, we generalize a well-established discrete-modulated continuous-variable (CV) QKD protocol from the point-to-point to the point-to-multipoint setting. We present a comprehensive security analysis across different scenarios and derive secret key rates for loss-only and noisy channels, both in the asymptotic and the composable finite-size regime. Experimentally, we validate the protocol in a passive optical network with 10 km access links, achieving a composable secure key rate of 2.185×10 −3 bits per symbol (0.273 Mbit/s) against independent and identically distributed collective attacks. Our results demonstrate that discrete-modulated CV-QKD can support access networks with multiple users while relying solely on cost-efficient, off-the-shelf telecommunication components, paving the way toward practical, scalable, and secure quantum networks.
Continuous-variable quantum key distribution (CVQKD) offers high key rates and compatibility with classical optical communications. Developing scalable and efficient CVQKD networks will facilitate the deployment of large-scale quantum communication networks. This paper proposes a CVQKD network based on the untrusted entanglement states of an optical frequency comb. The scheme generates Einstein-Podolsky-Rosen states with a frequency comb structure via a type-II optical parametric oscillator. By employing the entanglement-in-the-middle scheme, a source-untrusted fully connected CVQKD network capable of distributing secret keys simultaneously can be formed. We analyze the security of the system in the asymptotic and finite-size cases. Simulation results show that with careful control of system loss and noise, the proposed scheme is feasible for deploying a short-distance fully connected CVQKD network. Loss will be the main factor limiting system performance. The proposed scheme offers a new perspective for a multi-user fully connected CVQKD network.