Introduction: Continuous-variable quantum teleportation and entanglement distribution are fundamental building blocks for future quantum internet infrastructures. Quantum passive optical networks (QPONs) provide a promising architecture for scalable multi-user quantum communication by exploiting the mature passive optical network infrastructure. Materials and methods: We develop a theoretical framework for continuous-variable entanglement distribution and quantum teleportation in QPONs using two-mode squeezed vacuum states propagating through splitter–combiner–loss channels. Both downlink and uplink architectures are investigated under assisted and non-assisted protocols. The performance is analyzed using covariance matrix formalism, logarithmic negativity, and teleportation fidelity, and closed-form analytical expressions are derived together with numerical evaluations. Results: The analysis demonstrates that downlink entanglement distribution consistently outperforms the uplink architecture in terms of both logarithmic negativity and teleportation fidelity except in noise-less channels. Assisted protocols further enhance the achievable performance compared with non-assisted schemes. We derive the optimum squeezing parameter for non-assisted teleportation, showing that excessive squeezing may become detrimental because of network loss and splitting. Numerical results quantify the effects of network size, transmission distance, channel excess noise, detector imperfections, and measurement-added noise on entanglement distribution and teleportation performance. Also, we have showed that the time-division multiple-access is the preferred scheduling scheme between the users. Conclusions: The proposed framework establishes fundamental performance limits for continuous-variable QPONs and identifies practical design guidelines for scalable quantum access networks. The results demonstrate the advantages of downlink entanglement distribution and assisted teleportation, providing theoretical support for the development of future multi-user quantum communication and quantum internet infrastructures.
Introduction: Continuous-variable quantum teleportation and entanglement distribution are fundamental building blocks for future quantum internet infrastructures. Quantum passive optical networks (QPONs) provide a promising architecture for scalable multi-user quantum communication by exploiting the mature passive optical network infrastructure. Materials and methods: We develop a theoretical framework for continuous-variable entanglement distribution and quantum teleportation in QPONs using two-mode squeezed vacuum states propagating through splitter–combiner–loss channels. Both downlink and uplink architectures are investigated under assisted and non-assisted protocols. The performance is analyzed using covariance matrix formalism, logarithmic negativity, and teleportation fidelity, and closed-form analytical expressions are derived together with numerical evaluations. Results: The analysis demonstrates that downlink entanglement distribution consistently outperforms the uplink architecture in terms of both logarithmic negativity and teleportation fidelity except in noise-less channels. Assisted protocols further enhance the achievable performance compared with non-assisted schemes. We derive the optimum squeezing parameter for non-assisted teleportation, showing that excessive squeezing may become detrimental because of network loss and splitting. Numerical results quantify the effects of network size, transmission distance, channel excess noise, detector imperfections, and measurement-added noise on entanglement distribution and teleportation performance. Also, we have showed that the time-division multiple-access is the preferred scheduling scheme between the users. Conclusions: The proposed framework establishes fundamental performance limits for continuous-variable QPONs and identifies practical design guidelines for scalable quantum access networks. The results demonstrate the advantages of downlink entanglement distribution and assisted teleportation, providing theoretical support for the development of future multi-user quantum communication and quantum internet infrastructures.
We have investigated the entanglement distribution and quantum teleportation in quantum passive optical networks, where an entangled state is distributed between the central node and multiple end users through lossy fibers and passive optical splitter/combiner. The entanglement degradation is quantified using logarithmic negativity and teleportation fidelity, both in nonassisted and assisted strategies. We find that nonassisted teleportation fidelity rapidly drops below the classical limit as the number of users increases (possible up to five users), while assisted teleportation remains robust against both network size and photon loss, provided that the distributed entangled resource has sufficiently high fidelity. These results highlight the fundamental limitations of bipartite schemes and establish cooperative assisted strategies as essential primitives for scalable fiber-to-the-home quantum access networks and the quantum internet with several end users.
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.
Quantum teleportation (QT) over satellite-based free-space optical (FSO) channels is a promising approach for long-distance quantum communication. However, its performance is significantly degraded by atmospheric loss and turbulence. In this paper, we investigate continuous-variable (CV) QT in a dual-downlink scenario, where a satellite distributes entangled states to two ground stations. To mitigate channel-induced degradation, we employ a non-Gaussian entanglement distillation protocol based on the sequential application of photon addition and photon subtraction (PA-PS) on the weaker channel. The results show that the proposed scheme improves teleportation fidelity by up to 7.7% and enhances entanglement negativity by approximately 105% in the low-to-moderate (below 600 km) loss regime. In addition, we identify an optimal squeezing parameter that balances entanglement strength and noise sensitivity. Taken together, these results demonstrate the effectiveness of PA-PS distillation for improving CV quantum communication in realistic satellite networks. We further characterize the trade-off between fidelity gain and the heralded success probability of the protocol.
To establish a scalable and secure quantum network, a critical milestone is advancing from basic point-to-point quantum key distribution (QKD) systems to the development of inherently multi-user protocols designed to maximize network capacity. Here, we propose a quantum passive optical network (QPON) protocol based on continuous-variable (CV) systems, particularly the quadrature of the coherent state, which enables deterministic, simultaneous, and high-rate secret key generation among all network users. We implement 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 the users, we reach 1.5 and 2.1 Mbits/s of total network key generation (or 0.4 and 1.0 Mbits/s with finite-size channels estimation). Demonstrating the potential to expand the network's capacity to accommodate tens of users at a high rate, our CV-QPON protocols open up new possibilities in establishing low-cost, high-rate, and scalable secure quantum access networks serving as a stepping stone towards a quantum internet.
Abstract Quantum network scales the advantages of quantum communication protocols to more than two detached users, which offers great potential to realize the quantum internet. Here, a fully connected continuous‐variable (CV) quantum teleportation network architecture is presented, in which a squeezed state of light distributes each pair of entangled sideband modes to each communication link that bridges any pair of users. The quantum teleportation scheme is similar to standard two‐party ones for each communication link, without sacrificing communication capability and reliability. The demonstration based on CV‐entangled sideband modes opens an innovative possibility to implement many tasks of deterministic quantum information processing.