Content area
Full Text
The theoretically proven security of quantumkey distribution(QKD) could revolutionize the way in which information exchange is protected in the future1,2. Several field tests ofQKDhave proven it to be a reliable technology for cryptographic key exchange and have demonstrated nodal networks of point-to-point links3-5.However, until now no convincing answer has been given to the question of how to extend the scope of QKD beyond niche applications in dedicated high security networks. Here we introduce and experimentally demonstrate the concept of a 'quantum access network': based on simple and costeffective telecommunication technologies, the scheme can greatly expand the number of users in quantum networks and therefore vastly broadentheir appeal.We show that a high-speed single-photon detector positioned at a network node can be shared between up to 64 users for exchanging secret keys with the node, thereby significantly reducing the hardware requirements for each user added to the network. This point-to-multipoint architecture removes one of the main obstacles restricting the widespread application of QKD. It presents a viable method for realizing multi-user QKD networks with efficient use of resources, and brings QKD closer to becoming a widespread technology.
(ProQuest: ... denotes formulae omitted.)
In a nodal QKD network, multiple trusted repeaters are connected by means of point-to-point links between a quantum transmitter ('Alice') and a quantum receiver ('Bob'). These point-to-point links can be realized with long-distance optical fibres, and in the futuremight even use groundto- satellite communication6-8. Although point-to-point connections are suitable to form a backbone quantum core network to bridge long distances, they are less suitable to provide the last-mile service needed to give a multitude of users access to this QKD infrastructure. Reconfigurable optical networks based on optical switches or wavelengthdivision multiplexing have been suggested to achieve more flexible network structures3,9-12; however, they also require the installation of a full QKD system for each user, which is prohibitively expensive for many applications.
Giving a multitude of users access to the nodal QKD network requires point-to-multipoint connections. In modern fibre-optic networks point-to-multipoint connections are often realized passively by using components such as optical power splitters13. Single-photonQKD with the sender positioned at the network node and the receiver at the user premises14 lends itself naturally to a passivemulti-user network (see Fig. 1a). However, this downstream implementation has...