The Blind Copier Bench

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

Court's still in session, recruit, and now you get to run the Echo Network's own defense experiment for them.

Pick a state for the VIP qubit: a plain rectilinear |0⟩ or |1⟩, or a diagonal |+⟩ or |−⟩. Then pick which basis the judge checks the "clone" in. Run the hundred-shot test and compare the two histograms side by side.

Feed it a rectilinear state and the copier isn't lying: no entanglement was ever created, so it's a genuinely honest pair of qubits. Feed it a diagonal state, though, and the copier secretly produced an entangled Bell pair instead of two independent copies. Check it in the wrong basis and the fraud slips through unnoticed. Check it in the right one, the diagonal basis the state actually lives in, and the forgery collapses to a flat, useless 50/50, exactly the mismatch-destroys-everything lesson from Module 2, now used as a courtroom weapon.