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A textbook approach, attributed to Charlie Bennett, for creating reversible circuit which outputs the input qubits and the initialized ancilla qubits involves copying the function output between the two blocks - the forward and the reverse function. As can be seen in this figure

enter image description here

My question is, aren't the copied function qubits entangled to the internal qubits which are being zeroed by the reverse circuit?

Does this trick only work when the function output qubits are in the eigenstates (either |0⟩ or |1⟩)?

Mark Spinelli
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inq
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1 Answers1

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Yes, it will work fine. If a classical reversible circuit works on every classical basis state, it will also work on superpositions of those states. Try it in a simulator.

Of course, the output qubit at the bottom will end up entangled with the inputs. But that is intended.

Craig Gidney
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