Bell Basis Decoder

Your partner lab reads Bell pairs with a fixed lookup table: the parity bit (is it a Psi state?) must land on qubit 0, and the phase bit (is it a minus state?) on qubit 1. The textbook decoder gets this backwards.

Objective

Return a two-qubit circuit with two classical bits that rotates the Bell basis into the computational basis and measures qubit i into clbit i, so Phi+ -> 00, Psi+ -> 01, Phi- -> 10, Psi- -> 11 (labels are q1 q0).

Entry Point

Checks

• Exports build_bell_measurement().
• Each Bell state is mapped deterministically to its required label.
• Measures qubit 0 into clbit 0 and qubit 1 into clbit 1.