Uncrackable quantum encryption codes could be finding their way to mainstream networks. The new system, developed by Toshiba’s Cambridge Research Laboratory, allows dozens of users to share one network. Usually, each computer has to have an expensive and complicated transmitter and detector, as well as a fibre link. The networks work by transferring single photons of light in a sequence. If they’re observed en route, they change, making the code uncrackable in the laws of physics.