Quantum cryptography is the first technology in the area of quantum information that is in the process of making the transition from purely scientific research to an industrial application. The last ten years have seen dramatic advances in experimental quantum cryptography systems and several companies have developed quantum cryptography prototypes. Quantum Key Distribution (QKD) offers an information-theoretically secure way of communication but the practical applicability of QKD is severely curtailed by the fact that most implementations and protocols are limited to two communicating users. 

The pressing need to adapt quantum communication to quantum networks has motivated several attempts to connect more than two parties. To name the two most important networks types: Trusted-node networks: They amount to a mesh of point-to-point links, implemented by a separate and complete two-party communication setup. However, these trusted nodes relinquish the strong security offered by quantum cryptography. Further, this approach, duplicates resources like sender and receiver hardware and is therefore expensive and wasteful. The other type of networks are access networks: Usually a switch is used to temporally establish a quantum channel between two users. This approach suffers from the disadvantage of having an active component which ultimately puts a limit on the bandwidth that can be achieved. Also, not all connections are established simultaneously.  


We present a new type of network that combines the advantages of both: As in a trusted-node network,  our network architecture can form arbitrary network topologies, and -- very much like the access network -- we save resources by using only one source to serve all clients via only one fiber each. 


1.) S. Wengarowsky et al., arxiv.org/abs/1801.06194

2.) 1. Ursin R, Hughes R. Quantum information: Sharing quantum secrets. Nature 501(7465):37–8 (2013)