Cryptography has had a long and distinguished history of military and diplomatic use dating back to the ancient Greeks. But secure communications are becoming increasingly important for commercial applications as well.
Over the last few years, rapid progress has been made in the field of "quantum cryptography" in which information is carried by single quantum states. Quantum cryptography has been demonstrated by sending polarized photons through optical fibres that are tens of kilometres in length. The latest experiments show that single photons can now be transmitted securely over long distances without the use of fibre optics.
In the May issue of Physics World, Richard Hughes and Jane Nordholt from Los Alamos National Laboratory explain their latest research into quantum cryptography.