Multiple choice
Run this circuit. What is qubit 0's Bloch X-component — the expectation value ⟨X⟩?
const c = circuit(3); // 1. Encode |+_L>. c.h(0); c.cx(0, 1); c.cx(0, 2); // 2. Inject an X error on qubit 2. c.x(2); // 3. Decode (CNOT is self-inverse). c.cx(0, 1); c.cx(0, 2); // 4. Coherent majority correction onto the data qubit. c.ccx(2, 1, 0); return c;
Commit your prediction for ⟨X⟩ of qubit 0 — then run it.