Practical repeaters for ultra-long distance quantum communication

The problem of distributing a secret key by quantum channels is one of the preeminent problems in quantum information. To construct such a quantum channel, it is useful to use quantum repeaters, which shorten the distance over which individual photons need to be sent, and thus overcoming the problem of attenuation. Here, we present a method by which a quantum repeater network may be constructed using only existing technology. By taking advantage of the robustness of the processes of double-heralding and brokering, a thorough analysis of the system shows that this gives secret key rates on the order of kilohertz, even over distances of thousands of kilometres.