Input State |ψ⟩ = α|0⟩ + β|1⟩
Fidelity: —
Step 0: Alice has |ψ⟩ = α|0⟩+β|1⟩. She and Bob share Bell pair |Φ⁺⟩ = (|00⟩+|11⟩)/√2.
Step 1: Alice applies CNOT (|ψ⟩ as control, her Bell qubit as target).
Step 2: Alice applies Hadamard to |ψ⟩. State = entangled 4-qubit.
Step 3: Alice measures both qubits in Z-basis → 2 classical bits (m1, m2).
Step 4: Alice sends bits to Bob (classical channel). Bob applies X^m2 Z^m1 to recover |ψ⟩.
Result: Bob's qubit = |ψ⟩. Alice's original state is destroyed. Fidelity = 1.0 (ideal).