Alan Turing and an army of codebreakers took years to crack the Enigma code during the second world war. Just be thankful the Nazis weren't using a quantum Enigma machine.
Quantum key distribution (QKD) can already keep secret the key to a code. "I was trying to think of alternatives," says Seth Lloyd at the Massachusetts Institute of Technology. "It occurred to me that it would be interesting to quantise the Enigma machine."
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