Quantum cryptography is back in the news, and the basic idea is still unbelievably cool, in theory, and nearly useless in real life.
The idea behind quantum crypto is that two people communicating using a quantum channel can be absolutely sure no one is eavesdropping. Heisenberg's uncertainty principle requires anyone measuring a quantum system to disturb it, and that disturbance alerts legitimate users as to the eavesdropper's presence. No disturbance, no eavesdropper -- period.
Quantum channel means that the medium of transport is extremely small, for instance, a stream of individual photons.