Business Week has an accessible article on quantum cryptography. Quantum cryptography encodes information in the the orientation of photons and relying on Heisenberg's Uncertainty Principle to detect eavesdroppers. If you're looking for more information than what's available in the BW article try the following:
- BBN intro page on quantum cryptogrpahy
- Recent Red Herring technology brief on quantum cryptogrpahy
- A more technical article in Physic's Today from 2000 called From Quantum Cheating to Quantum Security
