Locking the sophisticated and expensive entanglement sources at the shared relay node is a promising choice for building a star-type quantum network with efficient use of quantum resources, where the involved parties only need to equip low-cost and simple homodyne detectors. Here, to our best knowledge, we demonstrate the first experimental continuous variable quantum key distribution with an entanglement source between the two users. We consider a practical partially characterized entangled source and establish the security analysis model of the protocol under realistic conditions. By applying a biased base technology, the higher key rate than that of the original protocol is achieved. The experimental results demonstrate that the distance between two users can reach up to 60 km over telecom single-mode fiber, implying the feasibility for high-rate and secure communication with a shared entangled source at metropolitan distances.
Locking the sophisticated and expensive entanglement sources at the shared relay node is a promising choice for building a star-type quantum network with efficient use of quantum resources, where the involved parties only need to equip low-cost and simple homodyne detectors. Here, to our best knowledge, we demonstrate the first experimental continuous variable quantum key distribution with an entanglement source between the two users. We consider a practical partially characterized entangled source and establish the security analysis model of the protocol under realistic conditions. By applying a biased base technology, the higher key rate than that of the original protocol is achieved. The experimental results demonstrate that the distance between two users can reach up to 60 km over telecom single-mode fiber, implying the feasibility for high-rate and secure communication with a shared entangled source at metropolitan distances.
Establishing a high-rate, cost-effective, and secure quantum communication network is critical for developing the quantum internet. A promising approach is to place a complex and expensive entangled source at a shared central node, which allows for efficient utilization of quantum resources in constructing a star-shaped downstream quantum access network. In this study, we propose a continuous-variable quantum passive optical network (CV-QPON) that employs a shared entangled source. We evaluate the network's security under two scenarios: one with a fully characterized entangled source and the other with a partially characterized entangled source. Both scenarios involve practical mixed entangled states. By combining the biased basis scheme, the renovated protocol outperforms the previous coherent state protocols in the secret key rate, transmission distance, the number of supported users, and tolerable excess noise. The results indicate that for a fully characterized entangled source, even at a transmission distance of 50 km, a moderate entangled source with 7 dB squeezing can still support up to 256 users accessing the network. Our scheme for a partially characterized entangled source relaxes the security assumptions regarding the central node, which is crucial for the downstream CV-QPON system. In this case, a 7 dB squeezing entangled source achieves a positive key rate for 64 users over a 30 km transmission distance, and it can even support up to 128 users at a 10 km transmission distance. With a 10 dB squeezing entangled source, 256 users can still be supported at a 30 km transmission distance. Furthermore, we analyze the protocol's security in the finite-size scenario and identify an optimal biased basis ratio that maximizes the key rate of the protocol. Given the rapid advancements in integrated entangled sources, our scheme offers a promising pathway for developing low-cost, high-rate, high-security, and large-scale quantum communication networks.
We experimentally demonstrated an all-fiber-based unidimensional continuous-variable quantum key distribution (CV QKD) protocol and analyzed its security under collective attack in realistic conditions. A pulsed balanced homodyne detector, which could not be accessed by eavesdroppers, with phase-insensitive efficiency and electronic noise, was considered. Furthermore, a modulation method and an improved relative phase-locking technique with one amplitude modulator and one phase modulator were designed. The relative phase could be locked precisely with a standard deviation of 0.5\ifmmode^\circ\else\textdegree\fi{} and a mean of almost zero. Secret key bit rates of 5.4 kbps and 700 bps were achieved for transmission fiber lengths of 30 and 50 km, respectively. The protocol, which simplified the CV QKD system and reduced the cost, displayed a performance comparable to that of a symmetrical counterpart under realistic conditions. It is expected that the developed protocol can facilitate the practical application of the CV QKD.
Quantum key distribution with continuous variables (CV-QKD) enables two parties to share a secret key by using coherent states of light and homodyne detection. This can be carried out by employing low-cost and mature technology developed for telecommunications. It has been shown that at short distances, CV-QKD allows for higher bit rates than conventional discrete variable QKD protocols. Furthermore, CV-QKD could potentially be employed to build a link for secure communication between two parties inside a building or campus and potentially in satellite communications. In this work, we will direct efforts into developing a fiber-based, low-cost, robust, and high-bitrate CV-QKD link. The theoretical concepts, specifics of the QKD system subsequently put into practice in the implementation, have been detailed. Finally, interference experiments have been performed parallel to the proof-of-principle QKD system.
A quantum key distribution network enables pairs of users to generate independent secret keys by leveraging the principles of quantum physics. For end-to-end secure communication, a user pair's secret key must remain secure against any third parties, including both external eavesdroppers and other network users. However, isolating a given user pair from the remaining users while maintaining a high key rate is challenging when all users are intrinsically correlated, particularly in continuous-variable networks. This results in either a low key rate or incomplete end-to-end security. Here, we introduce a multiuser security framework, offering a general and comprehensive end-to-end key rate formula, against the worst-case scenario where an eavesdropper fully exploits the user crosstalk. Building on this framework, we propose a multiuser protocol that achieves the theoretical upper limit in all practical deployments within a 100 km range. Applied to a three-node network, it achieves an Mbps-level per-user key rate and an overall network key rate reaching 90% of the upper limit. The proposed solution supports scalable implementations using telecom-compatible components, while the method for obtaining the accessible information in the network is broadly applicable and can be extended to various multipartite quantum information systems.
Secure communication protocols based on quantum physics compel worldwide attention. Continuous-variable quantum key distribution (CV-QKD) uses a cost-effective detection technique instead of dedicated single-photon-counting technology, and can provide high key rates over metropolitan distances. Traditional coherent-state CV-QKD protocols, however, suffer from low tolerance of channel excess noise. The authors succeed in distributing Einstein-Podolsky-Rosen entangled states over a 50-km standard fiber with negligible excess noise, and further demonstrate CV-QKD in a high-noise environment with performance superior to that of the optimized coherent-state protocol.
We report on the design and field validation of a fully connected entanglement-based quantum key distribution (QKD) network employing a time-shared photon-pair source and reconfigurable optical switching. The system eliminates the need for trusted relay nodes and enables any-to-any secure connectivity among users over metropolitan-scale fiber infrastructure. We present a three-node prototype network operating in the O-band(1310/1316nm)which demonstrates key generation sufficient to provide pairwise 10 G encrypted connections between 32 users, and confirming practical feasibility for telecom integration.