Ex5 9

$\def\abs#1{|#1|}\def\i{\mathbf {i}}\def\ket#1{|{#1}\rangle}\def\bra#1{\langle{#1}|}\def\braket#1#2{\langle{#1}|{#2}\rangle}\def\tr{\mathord{\mbox{tr}}}\mathbf{Exercise\ 5.9}$

How can the circuit

be used to measure the qubits $b_0$ and $b_1$ for equality without learning anything else about the state of $b_0$ and $b_1$? (Hint: you are free to chose any initial state on the register consisting of qubits $a_0$ and $a_1$.)

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