qiskit/releasenotes/notes/2.0/cc-gate-fidelity-bde7a01dc8...

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---
upgrade:
- |
Increased the minimum threshold for when gates are assumed to be the identity in
:class:`.RemoveIdentityEquivalent` from machine epsilon to ``1e-12`` to
account for round-off errors in the fidelity calculation and for consistency with the
other classes, such as :class:`.CommutationAnalysis` and :class:`.TwoQubitWeylDecomposition`.
- |
Updated the metric used to check commutations in :class:`.CommutationChecker`.
Two gates are assumed to commute if the average gate fidelity of the commutation is
above ``1 - 1e-12``. This value is chosen to account for round-off errors in the
fidelity calculation and for consistency with :class:`.RemoveIdentityEquivalent` and
:class:`.TwoQubitWeylDecomposition`. See the class docstring for more information.
fixes:
- |
Fixed an inconsistency in dealing with close-to-identity gates in the transpilation process,
where gates that are close to the identity were assumed to commute with everything, but
not removed. The underlying issue were different metrics used in :class:`.RemoveIdentityEquivalent`
and :class:`.CommutationAnalysis` (and, by extension, :class:`.CommutativeInverseCancellation`).
Both now use the average gate fidelity and the same threshold to assess whether a gate
should be treated as identity (such as a rotation gate with very small angle). See either
of the aforementioned classes' docstrings for more information.
Fixed `#13547 <https://github.com/Qiskit/qiskit/issues/13547>`__.
features_circuits:
- |
Added a new argument ``approximation_degree`` to :meth:`.CommutationChecker.commute` and
:meth:`.CommutationChecker.commute_nodes`, which allows to set the approximation threshold
for when gates are said to commute. See the docstring of :class:`.CommutationChecker` for more
detail.
features_transpiler:
- |
Added a new argument ``approximation_degree`` to :class:`.CommutationAnalysis`, which allows
setting the approximation threshold for when gates are said to commute. See the class docstring
for more information.