The ability to send perfectly secure messages from one location on the planet to another has obvious and immediate appeal to governments, the military and various commercial organisations such as banks.

 

This capability is already possible over short distances thanks to the magic of quantum cryptography, which guarantees the security of messages, at least in theory.

For the moment, however, quantum cryptography works only over distances of 100 km or so. That’s how far it is possible to send the single photons that carry quantum messages through an optical fibre or through the atmosphere.