Quantum physics offers James Bond and his ilk much more than a bit of solace—it permits quantum encryption, a completely spyproof way to send coded information. Eavesdropping by a third party can always be detected.
But now physicists have suggested that quantum codes may be breakable. The feat involves a trick that even Bond hasn’t mastered yet — time travel. By taking advantage of hidden paths to the past — routes that are predicted by some of Einstein’s equations — a nemesis could eavesdrop on a quantum-coded message without being detected.
Time travel, such as, say, through a “wormhole,” appears to make it possible to distinguish quantum information that usually can’t be distinguished. That ability would disrupt the absolute security of quantum encryption, theoretical physicist Todd Brun and collaborators report online in the quantum physics archive (arXiv:0811.1209v1).
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