Bell State Quartet

Everyone learns |Phi+>. A Bell-basis lab needs all four maximally entangled states on demand, and they differ only by which X and Z you apply before entangling.

Objective

create_bell_circuit(which) receives one of "phi+", "phi-", "psi+", "psi-" and returns a two-qubit circuit preparing (|00> + |11>)/sqrt(2), (|00> - |11>)/sqrt(2), (|01> + |10>)/sqrt(2) or (|01> - |10>)/sqrt(2) respectively.

Constraints

• No initialize / state_preparation shortcuts.

Entry Point

Checks

• Exports create_bell_circuit(which).
• All four Bell states match up to global phase.