A quantum access network

Abstract

The theoretically proven security of quantum key distribution (QKD) could revolutionise how information exchange is protected in the future [1,2]. Several field tests of QKD have proven it to be a reliable technology for cryptographic key exchange and have demonstrated nodal networks of point-to-point links [3][4][5]. However, so far 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 show that adopting simple and cost-effective telecommunication technologies to form a quantum access network can greatly expand the number of users in quantum networks and therefore vastly broaden their appeal. We are able to demonstrate 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 realising multi-user QKD networks with resource efficiency and brings QKD closer to becoming the first widespread technology based on quantum physics.In a nodal QKD network multiple trusted repeaters are connected via point-to-point links between a quantum transmitter (Alice) and a quantum receiver (Bob). These point-to-point links can be realised with long-distance optical fibres, and in the future might even utilize ground to satellite communication [6][7][8]. While 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 wavelength-division multiplexing have been suggested to achieve more flexible network structures[3, 9-12], however, they also require the installation of a full QKD system per 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 using components such as optical power splitters [13]. Single photon QKD with the sender positioned at the network node and the receiver at the user premises[14] lends itself naturally to a passive multi-user network (see Fig. 1a). However, this downstream implementation has two major shortcomings. Firstly, every user in the network requires a single photon detector, which are often expensive and difficult to operate. And secondly, it is not possible to deterministically address a user. All detectors therefore have to operate at the same speed as the transmitter in order not to miss photons, which means most of the detector bandwidth is unused.Here, we show that both problems associated with a downstream implementation can be overcome ...

Quantum key distribution without detector vulnerabilities using optically seeded lasers

“…1(a), two light pulses are independently encoded and sent by Alice and Bob to a central node, Charlie. This is similar to a quantum access network configuration [20], but in MDI-QKD the central node does not need to be trusted and could even attempt to steal information from Alice and Bob. To follow the MDI-QKD protocol, Charlie must let the two light pulses interfere at the beam splitter inside his station and then measure them.…”

Field and long-term demonstration of a wide area quantum key distribution network

“…Based on the passive beam splitter, Townsend et al presented and realized the first QKD network [17,18]. And since then, researchers have devised and developed an impressive collection of network architectures for QKD [19][20][21][22][23][24][25][26][27][28][29][30][31]. Combined with increasingly mature QKD devices, these developments enabled QKD networks to be deployed over real-world telecommunication networks.…”

An entangled-LED-driven quantum relay over 1 km

“…Quantum key distribution 1,2 systems based on weak-coherent optical pulses have been reported that allow unique cryptographic keys to be shared between directly connected users on point-to-point [3][4][5] or point-to-multipoint links 6 . To establish fully quantum multipartite networks, that avoid trusting intermediate parties, 7 it is necessary to route quantum signals through a backbone of quantum nodes.…”