This advance is limited to fibre optic networks but other scientists are beginning to consider how quantum keys can be shared over satellite or wireless networks.
Richard Hughes and his colleagues at the Los Alamos National Laboratory, in New Mexico, and several other teams have been working on a new way to share a quantum key transmitted by photons, so that it can be exchanged over radio networks.
Hughes has no illusions about the difficulty of this task.
"One must face the much more challenging problem of transmitting the quantum key distribution (QKD) photons through the atmosphere and reliably selecting them out from the huge background of light that is present even at night," he said.
The latest steps towards developing an uncrackable code are in latest edition of the New Journal of Physics, which is published by the Institute of Physics and the German Physical Society.
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