Quantum key distribution (QKD) is an exciting application of quantum technologies that has exploded in the past decade.  QKD is used to share encryption keys across an established optical link or network. QKD can be used to generate a secure, shared secret key between two users. This key is then used in an algorithm to encrypt message traffic.  The big advantage QKD offers is that any attempt to read the information stored in the photons would destroy the message and be immediately detected. Quantum cryptography is fundamentally viable today in the laboratory and used in some high-end security applications, like banking and stock trading, that can rely on dedicated short distance physical fibers.