Photons and other subatomic particles can be encoded with cryptographic keys—the kind used to scramble and unscramble messages. The state of a particle changes as soon as it is intercepted, making it impossible for a third party to steal the key without alerting the intended recipient. Quantum encryption can be defeated when it isn’t used properly, said Alexander Ling, an expert in quantum communications at the Center for Quantum Technologies in Singapore. Deployed correctly, quantum encryption would protect data against conventional snooping and protect networks against efforts in the U.S. and elsewhere to build quantum computers powerful enough to defeat the math-based encryption currently in use.

https://www.wsj.com/articles/scientists-make-leap-toward-quantum-network-1497549676