Quantum networks scale the advantages of quantum communication protocols to more than just two distant users. Here we present a fully connected quantum network architecture in which a single entangled photon source distributes quantum states to a multitude of users. Our network architecture thus minimizes the resources required of each user without sacrificing security or functionality. As no adaptations of the source are required to add users, the network can readily be scaled to a large number of clients, whereby no trust in the provider of the quantum source is required. Unlike previous attempts at multi-user networks, which have been based on active components, and thus limited to some duty cycle, our implementation is fully passive and thus provides the potential for unprecedented quantum communication speeds. We experimentally demonstrate the feasibility of our approach using a single source of bi-partite polarization entanglement which is multiplexed into 12 wavelength channels to distribute 6 states between 4 users in a fully connected graph using only 1 fiber and polarization analysis module per user. We then discuss practical usage scenarios to demonstrate the advantage of some of the salient features of our network topology. These include adaptations/hardware implementations that are more favorable for local area networks and those for long distance intercity links. Our implementation consisted of a single Type 0 MgO:PPLN crystal pumped bidirectionally in a Sagnac interferometer to produce polarization entangled photon pairs with an ≈ 60 nm bandwidth. These pair wise entangled photons were split into 12 different wavelength channels corresponding to 6 correlated wavelength pairs. Each of the 4 users in our demonstration received 3 wavelength channels multiplexed together via a solitary single mode fiber. Each user had just one detector unit that they used to simultaneously measure all input channels. We exploited small time delays between different channels to isolate the relevant signal from noise. We measured the quality of entanglement between each channel pair simultaneously and calculated the effective secure key rate using the E91 protocol. Our experiment showed the effectiveness of our network topology and its scalability against noise, number of users and losses. Further experiments are underway to increase the number of clients and improve the scalability of the topology. Also, we plan to demonstrate distributed computation tasks like secure auctions, Byzantine fault tolerance, and asynchronous reference frame agreement are feasible using our network architecture.Quantum networks scale the advantages of quantum communication protocols to more than just two distant users. Here we present a fully connected quantum network architecture in which a single entangled photon source distributes quantum states to a multitude of users. Our network architecture thus minimizes the resources required of each user without sacrificing security or functionality. As no adaptations of the source are required to add users, the network can readily be scaled to a large number of clients, whereby no trust in the provider of the quantum source is required. Unlike previous attempts at multi-user networks, which have been based on active components, and thus limited to some duty cycle, our implementation is fully passive and thus provides the potential for unprecedented quantum communication speeds. We experimentally demonstrate the feasibility of our approach using a single source of bi-partite polarization entanglement which is multiplexed into 12 wavelength channels to distribute 6 states between 4 users in a fully connected graph using only 1 fiber and polarization analysis module per user. We then discuss practical usage scenarios to demonstrate the advantage of some of the salient features of our network topology. These include adaptations/hardware implementations that are more favorable for local area networks and those for long distance intercity links. Our implementation consisted of a single Type 0 MgO:PPLN crystal pumped bidirectionally in a Sagnac interferometer to produce polarization entangled photon pairs with an ≈ 60 nm bandwidth. These pair wise entangled photons were split into 12 different wavelength channels corresponding to 6 correlated wavelength pairs. Each of the 4 users in our demonstration received 3 wavelength channels multiplexed together via a solitary single mode fiber. Each user had just one detector unit that they used to simultaneously measure all input channels. We exploited small time delays between different channels to isolate the relevant signal from noise. We measured the quality of entanglement between each channel pair simultaneously and calculated the effective secure key rate using the E91 protocol. Our experiment showed the effectiveness of our network topology and its scalability against noise, number of users and losses. Further experiments are underway to increase the number of clients and improve the scalability of the topology. Also, we plan to demonstrate distributed computation tasks like secure auctions, Byzantine fault tolerance, and asynchronous reference frame agreement are feasible using our network architecture.

SPIE Quantum Information Science and TechnologyOct 11, 20181 citation

Free-space multi-user quantum network with high key rate

Ayan Kumar Nai, G. K. Samanta

Emergent quantum networks are the essential ingredient for securely connecting multiple users worldwide, extensively deployed in both fibre and free-space. An essential element is the multiplexing of entanglement to multiple users, overcoming the peer-to-peer restriction of quantum key distribution (QKD), so far successfully shown in fibre-based architectures. Here, we demonstrate a free-space quantum space division multiplexing architecture using just one entanglement source to realise a fully connected twelve-channel quantum network for seamless QKD connections between six users. The network achieves record coincidence rates exceeding $3 \times 10^{4}$ s $^{-1}$ between any pair of nodes on the network, for sifted key rate of over 400 kbps. Our approach overcomes the active switching hurdle that has hindered the free-space deployment of quantum multiplexing, is fully passive, easily scalable to more nodes and compatible with fibre-based integration, thus opening a new path to scalable and resource-efficient quantum networks that utilise free-space links.Emergent quantum networks are the essential ingredient for securely connecting multiple users worldwide, extensively deployed in both fibre and free-space. An essential element is the multiplexing of entanglement to multiple users, overcoming the peer-to-peer restriction of quantum key distribution (QKD), so far successfully shown in fibre-based architectures. Here, we demonstrate a free-space quantum space division multiplexing architecture using just one entanglement source to realise a fully connected twelve-channel quantum network for seamless QKD connections between six users. The network achieves record coincidence rates exceeding $3 \times 10^{4}$ s$^{-1}$ between any pair of nodes on the network, for sifted key rate of over 400 kbps. Our approach overcomes the active switching hurdle that has hindered the free-space deployment of quantum multiplexing, is fully passive, easily scalable to more nodes and compatible with fibre-based integration, thus opening a new path to scalable and resource-efficient quantum networks that utilise free-space links.

arXiv:2511.00466Nov 1, 20250 citations

Entanglement distribution quantum networking within deployed telecommunications fibre-optic infrastructure

M. J. Clark, Obada Alia, Rui Wang +12 more

Quantum networks have been shown to connect users with full-mesh topologies without trusted nodes. We present advancements on our scalable polarisation entanglement-based quantum network testbed, which has the ability to perform protocols beyond simple quantum key distribution. Our approach utilises wavelength multiplexing, which is ideal for quantum networks across local metropolitan areas due to the ease of connecting additional users to the network without increasing the resource requirements per user. We show a 10 user fully connected quantum network with metropolitan scale deployed fibre links, demonstrating polarisation stability and the ability to generate secret keys over a period of 10.8 days with a network wide average-effective secret key rate of 3.38 bps.Quantum networks have been shown to connect users with full-mesh topologies without trusted nodes. We present advancements on our scalable polarisation entanglement-based quantum network testbed, which has the ability to perform protocols beyond simple quantum key distribution. Our approach utilises wavelength multiplexing, which is ideal for quantum networks across local metropolitan areas due to the ease of connecting additional users to the network without increasing the resource requirements per user. We show a 10 user fully connected quantum network with metropolitan scale deployed fibre links, demonstrating polarisation stability and the ability to generate secret keys over a period of 10.8 days with a network wide average-effective secret key rate of 3.38 bps.

arXiv:2211.09051Quantum Technology: Driving Commercialisation of an Enabling ScienceJan 11, 20238 citations

A large-scale reconfigurable multiplexed quantum photonic network

Natalia Herrera Valencia, Annameng Ma, Suraj Goel +5 more

The distribution of entanglement in quantum networks will enable the next generation of technologies in quantum-secured communications, distributed quantum computing and sensing. Future quantum networks will require dense connectivity, allowing multiple users to share entanglement in a reconfigurable and multiplexed manner, while long-distance connections are established through the teleportation of entanglement, or entanglement swapping. Although several recent works have demonstrated fully connected, local multi-user networks based on multiplexing, extending such networks to a global network architecture of interconnected local networks remains an outstanding challenge. Here we demonstrate the next step in the evolution of multiplexed quantum networks-a prototype global reconfigurable network in which entanglement is routed and teleported in a flexible and multiplexed manner between two local four-user networks. At the heart of our network is a programmable 8 × 8-dimensional multi-port circuit that harnesses the natural mode-mixing process inside of a multi-mode fibre to implement on-demand high-dimensional operations on two independent photons carrying eight transverse-spatial modes. Our circuit design allows us to break away from the limited planar geometry and bypass the control and fabrication challenges of conventional integrated photonic platforms. Our demonstration highlights the potential of this architecture for enabling large-scale, global quantum networks that offer versatile connectivity while being fully compatible with an existing communications infrastructure.The distribution of entanglement in quantum networks will enable the next generation of technologies in quantum-secured communications, distributed quantum computing and sensing. Future quantum networks will require dense connectivity, allowing multiple users to share entanglement in a reconfigurable and multiplexed manner, while long-distance connections are established through the teleportation of entanglement, or entanglement swapping. Although several recent works have demonstrated fully connected, local multi-user networks based on multiplexing, extending such networks to a global network architecture of interconnected local networks remains an outstanding challenge. Here we demonstrate the next step in the evolution of multiplexed quantum networks-a prototype global reconfigurable network in which entanglement is routed and teleported in a flexible and multiplexed manner between two local four-user networks. At the heart of our network is a programmable 8 × 8-dimensional multi-port circuit that harnesses the natural mode-mixing process inside of a multi-mode fibre to implement on-demand high-dimensional operations on two independent photons carrying eight transverse-spatial modes. Our circuit design allows us to break away from the limited planar geometry and bypass the control and fabrication challenges of conventional integrated photonic platforms. Our demonstration highlights the potential of this architecture for enabling large-scale, global quantum networks that offer versatile connectivity while being fully compatible with an existing communications infrastructure.

arXiv:2501.07272Nature PhotonicsNov 26, 20256 citations

3 \times 10^{4}

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between any pair of nodes on the network, for sifted key rate of over 400 kbps. Our approach overcomes the active switching hurdle that has hindered the free-space deployment of quantum multiplexing, is fully passive, easily scalable to more nodes and compatible with fibre-based integration, thus opening a new path to scalable and resource-efficient quantum networks that utilise free-space links.