FAQ: WHICH QUBIT IS WHICH IN THE RESULTS? 🔢
The #1 source of "my circuit is broken" reports that aren't bugs:
In the results labels, qubit 0 is the LEFTMOST digit. So with two qubits, the outcome "10" means qubit 0 measured 1 and qubit 1 measured 0.
If you put an X gate on qubit 0 only and see "10" instead of "01" — that's not a bug, that's the convention. (Different textbooks and frameworks disagree on this ordering, which is why everyone gets bitten by it once.)
When in doubt: one qubit at a time, flip it with X, and see which digit moves.
The #1 source of "my circuit is broken" reports that aren't bugs:
In the results labels, qubit 0 is the LEFTMOST digit. So with two qubits, the outcome "10" means qubit 0 measured 1 and qubit 1 measured 0.
If you put an X gate on qubit 0 only and see "10" instead of "01" — that's not a bug, that's the convention. (Different textbooks and frameworks disagree on this ordering, which is why everyone gets bitten by it once.)
When in doubt: one qubit at a time, flip it with X, and see which digit moves.
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