Qiskit / qiskit / 34149608764

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Commit Message

speed up case of `BasePauli._evolve_clifford` (#16835)

* speed up case of `BasePauli._evolve_clifford`

The existing `BasePauli._evolve_clifford` was wasteful when evolving a mostly-idenity Pauli (or PauliList) by a many-qubit Clifford. (e.g. if we want to apply a many-qubit Clifford to a few-qubit Pauli, we first expand the Pauli with a bunch of identities before calling evolve).

It would loop in Python over all rows of the Clifford, checking each time whether that row should be applied (`idx_.any()`). If `self` has support on only a few qubits, most of the rows don't do anything, such that most of the python-loop iterations are no-ops.

New version moves the vectorized `any()` call outside of the loop, and then python-loops over only the necessary rows of `Clifford`.

* release note

* Reword release note

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Co-authored-by: Jake Lishman <jake.lishman@ibm.com>

Coverage Stats

4 of 4 new or added lines in 1 file covered. (100.0%)

25 existing lines in 4 files now uncovered.

116723 of 132856 relevant lines covered (87.86%)

982374.39 hits per line