Experts in atoms and other particles, these cryptologists want to exploit the laws of quantum mechanics to send messages that are provably unhackable. Quantum cryptography draws its strength from the weirdness of reality at small scales.
The most popular cryptographic application yet for this strange behavior is quantum key distribution, aka QKD. A quantum key encodes and sends the information needed to decrypt a message in the fuzzy properties of particles, typically light particles.
Eavesdroppers trying to steal the key must make measurements of those particles to do so. Many variations on QKD exist, some of which employ an unusual long-distance quantum connection called entanglement to protect information. Entanglement allows two particles to behave like a single entity, no matter how far apart they are.
The first quantum transaction took place in 2004, when researchers in Vienna used entangled photons to transfer a 3,000-Euro deposit into their bank account.