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Efforts to build a quantum internet are under way, but turning what was once a lab experiment into a robust, modern communications network is not without its difficulties. Now, two researchers have come up with a way to ensure quantum networks are unhackable, even at scale.
Theoretically, messages sent via quantum networks are secured by the laws of quantum mechanics, because any attempt to intercept information sent between two parties will disturb its fragile quantum state, revealing the eavesdropper. One way to check a quantum line is secure involves solving an equation called a Bell inequality – if the result exceeds a certain number, there is a limit to how much information a spy can extract without being detected.
But this is only true for messages sent between two points. On a more complex network, the Bell inequality doesn’t apply. That’s roughly because quantum hackers