An quantum access network, connecting multiple end users and a backbone network in a scalable and cost-effective way with tree or star structures, is suitable to combine with continuous-variable quantum key distribution for network security. Under the realistic condition, in a passive optical network in optical distribution network achieved by a practical passive beam splitter, it is hard to divide the signal into 1/n parts evenly. To well quantify the impact of the imperfection, we modify the formula for secret key rate calculation with the imperfection effect and conduct numerical simulations. The results indicate that if the communication parties neglect this imperfection, Eve can attack the entire network and attain information without the parties’ awareness.
An quantum access network, connecting multiple end users and a backbone network in a scalable and cost-effective way with tree or star structures, is suitable to combine with continuous-variable quantum key distribution for network security. Under the realistic condition, in a passive optical network in optical distribution network achieved by a practical passive beam splitter, it is hard to divide the signal into 1/n parts evenly. To well quantify the impact of the imperfection, we modify the formula for secret key rate calculation with the imperfection effect and conduct numerical simulations. The results indicate that if the communication parties neglect this imperfection, Eve can attack the entire network and attain information without the parties’ awareness.
Quantum key distribution (QKD), which enables the secure distribution of symmetric keys between two legitimate parties, is highly useful in future network security. An access network that connects multiple end users with one network backbone can be combined with QKD to build security for end users in a scalable and cost-effective way. In this paper, we show that a downstream-access network can be implemented using continuous-variable (CV) QKD. The security analysis is conducted independently with other network nodes, which greatly relax the trustfulness requirement on the network nodes. The security is then obtained against other network parties even when the quantum signals are broadcast throughout the network. The passive beam splitter is sufficient to deterministically distribute the quantum signals, and standard CV QKD systems can be directly fitted in the downstream-access network, which makes it more applicable for practical implementations. Numerous simulation results are provided to demonstrate the performance of the CV QKD downstream-access network, where up to 64 end users are shown to be feasible to access the network. We provide the security-analysis framework for realizing CV QKD in the downstream-access network, which will boost the diversity for constructing practical CV QKD networks.
Quantum key distribution (QKD) which enables the secure distribution of symmetric keys between two legitimate parties is of great importance in future network security. Access network that connects multiple end-users with one network backbone can be combined with QKD to build security for end-users in a scalable and cost-effective way. Though previous QKD access networks are all implemented in the upstream direction, in this paper, we prove that downstream access network can also be constructed by using continuous-variable (CV) QKD. The security of the CV-QKD downstream access network is analyzed in detail, where we show the security analysis is secure against other parties in the network. The security analysis we proved corresponds to the downstream access network where only passive beamsplitter is sufficient to distribute the quantum signals and no other active controls are demanded. Moreover, standard CV-QKD systems can be directly fitted in the downstream access network, which makes it more applicable for practical implementations. Numerous simulation results are provided to demonstrate the performance of the CV-QKD downstream access network, where up to 64 end-users are shown to be feasible to access the network. Our work provides the security analysis framework for realizing QKD in the downstream access network which will boost the diversity for constructing practical QKD networks.
Building scalable and secure quantum networks with many users has a high application potential but also holds many practical challenges. A significant stride in this pursuit involves extending quantum key distribution, an information-theoretically secure method for establishing cryptographic keys between two distant users, from a point-to-point protocol implemented on direct optical connections to a quantum access network. Yet, realizations of quantum access networks have, so far, relied on probabilistic or time-sharing strategies. Here, we show theoretically and experimentally that a solution without these constraints can come from the exclusive features of continuous-variable systems. Based on coherent states, we propose continuous-variable quantum passive-optical-network (CV-QPON) protocols, enabling deterministic and simultaneous secret key generation among all network users. We achieve this by leveraging the inherent wave-like property of coherent states split at a beam splitter and electric-field quadrature measurements. We show two protocols with different trust levels assigned to the network users and experimentally demonstrate key generation in a quantum access network with 8 users, each with an 11 km span of access link. Depending on the trust assumptions about users, we reach 1.5 Mbits/s and 2.1 Mbits/s of total network key generation. Demonstrating the potential to expand the network's capacity to accommodate tens of users at a high rate, our CV-QPON protocols offer a pathway toward establishing low-cost, high-rate, and scalable quantum access networks using standard telecom technologies and directly exploiting the existing access network infrastructure.
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.
Continuous variable quantum key distribution that can be implemented using only low-cost and off-the-shelf components reveals great potential in practical large-scale realization. Access networks, as a modern network necessity, connect many end-users to the network backbone. In this work, we first demonstrate upstream transmission quantum access networks using continuous variable quantum key distribution. A two-end-user quantum access network is then experimentally realized. Through phase compensation, data synchronization, and other technical upgrades, we achieve a secret key rate of the total network of 390 kbits/s. In addition, we extend the case of a two-end-user quantum access network to the case of a multiplicity of users, and analyze the network capacity in the case of a multiplicity of users by measuring the additive excess noise from different time slots.
It is well known that optical access networks are able to provide high data rates over long distances and to a reasonable number of users. Security and privacy are always a challenge for public accessible network infrastructures. Especially in time-division multiplexing passive optical networks (TDM-PONs), in which the downstream signal is broadcasted to all users connected via the same wavelength channel in a shared fiber link, privacy can be a critical concern. Although encryption at the application layer can provide a high level of security, this can be achieved only if the encryption key distribution is perfectly save. On the other hand, encryption on the physical layer such as quantum cryptography or, more precisely, quantum key distribution (QKD) is a very promising approach to achieve secure communication. However, there remain several issues that have to be solved before the quantum cryptography reaches the maturity level needed for a cost effective implementation in practical networks. In this paper, we address quantum key distribution (QKD) over passive optical access networks, which is an enabling technology required to cost efficiently deploy practical quantum encrypted data communication in the access area. We study different methods to integrate QKD systems in conventional optical access networks and quantitatively evaluate their suitability for a potential implementation.