The Echo Network vs Physics

Mission 3: The No-Cloning Mystery. Part of the Quantum Courier Service, a free course from the Oxford University Quantum Information Society.

In their hubris to steal a single secret, the Echo Network glued their spy equipment inextricably to our messenger's qubit. Nothing happens at our end when they read their "copy". No alarm sounds, no needle twitches, and that is exactly as it should be, or we'd have invented a telephone that beats light. What happens is quieter and worse for them: their qubit and ours are now correlated in a way that a clean channel never produces. The next time we compare notes with our messenger over an open line, the numbers won't add up, and there is no version of the story where they do.

The No-Cloning Theorem holds firm: The universe simply has the ultimate, unbreakable copyright protection.