Fig. 1
From: 40-user fully connected entanglement-based quantum key distribution network without trusted node
Illustration of network architecture depicting distribution of entanglement resources with different correlated wavelength channel pairs to users. Subscripts with opposite numbers represent wavelength channels corresponding to a specific entanglement resource. (a) Sketch of the intra-subnet layer. Entangled photon pairs with two correlated wavelength channels are distributed randomly to users by a passive beam splitter. As the signal and idler photons in a pair move randomly to the users, each user will have coincidence events with any other user. Hence, it constructs a fully connected QKD network without trusted node, thereby forming a subnet in the network architecture. (b) Sketch of the inter-subnet layer. Green and purple squares denote users in two subnets, which are supported by two entanglement resources (λ1/λ− 1 and λ2/λ− 2) separately. To establish connections between these two subnets, an additional entanglement resource (λ6/λ− 6) is used. The signal and idler photons of this resource are separated by wavelength division multiplexing components and distributed to users in these two subnets by the same passive beam splitters along with photons of wavelength λ1/λ− 1 or λ2/λ− 2 in the intra-subnet layer. Hence, each user in one subnet will have coincidence events with any user in the other subnet by sharing an entanglement resource. Therefore, all users in the network are fully connected. (c) Based on this two-layer network architecture, a fully connected QKD network with five subnets is constructed in this work. Each user receives six wavelength channels. Two of them belong to the pair of correlated wavelength channels supporting the connection in the subnet. The other four wavelength channels are used to connect the users between different subnets