Remove faulty qubits and gates sections from transpile() #9900
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This commit removes the "faulty qubits" support from the transpile(). Previously the transpile() function would attempt to filter out any faulty qubits or gates reported in a BackendV1's BackendProperties object and remap the qubits based on that. However, this code was never actually functioning as the first BackendV1 based backend to attempt to set these flags is causing an internal panic in rustworkx trying to created the remapped coupling map. This code path was mildly controversial at the time of introduction (and was already reverted once in the past) and since it provably isn't valid anymore (and I wasn't clear it ever functioned as expected) as the only backend to leverage the feature crashes transpile() this commit just opts to remove it as a potential breaking change.
mtreinish
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Changelog: Removal
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There's also a couple of minor references to faultiness in comments in DenseLayout and VF2's build_average_error_map that we might want to squash. For completeness for others: there's also test files test/python/providers/{faulty_backends.py,test_faulty_backend.py}, but those are testing the BackendV1 model not transpile so this PR needn't remove them.
Officially this PR isn't entirely within our deprecation policy because we haven't issued any warning before removing this implicit behaviour from the transpiler, but we judged the impact to be minimal as we're not aware of any current backends using this feature at all and in practice the handling doesn't actually work, so we don't think anybody can be using it. Offline, @1ucian0 (one of the original authors of the feature) also signed off on this removal.
edit: ha, I posted this comment then saw that Luciano had assigned himself to do a review as well.
releasenotes/notes/remove-faulty-qubits-support-00850f69185c365e.yaml
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confirming. Let's remove it. |
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do we want to keep the references in the following files?
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Besides #9900 (comment) (that can be in a follow up, if necessary), LGTM
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The second two references need to stay: |
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I went ahead and enqueued this for merging because of those remaining references only 1 arguably needs to be updated, but it's just a code comment |
* Remove faulty qubits and gates sections from transpile() This commit removes the "faulty qubits" support from the transpile(). Previously the transpile() function would attempt to filter out any faulty qubits or gates reported in a BackendV1's BackendProperties object and remap the qubits based on that. However, this code was never actually functioning as the first BackendV1 based backend to attempt to set these flags is causing an internal panic in rustworkx trying to created the remapped coupling map. This code path was mildly controversial at the time of introduction (and was already reverted once in the past) and since it provably isn't valid anymore (and I wasn't clear it ever functioned as expected) as the only backend to leverage the feature crashes transpile() this commit just opts to remove it as a potential breaking change. * Fix release note typos
* Remove faulty qubits and gates sections from transpile() This commit removes the "faulty qubits" support from the transpile(). Previously the transpile() function would attempt to filter out any faulty qubits or gates reported in a BackendV1's BackendProperties object and remap the qubits based on that. However, this code was never actually functioning as the first BackendV1 based backend to attempt to set these flags is causing an internal panic in rustworkx trying to created the remapped coupling map. This code path was mildly controversial at the time of introduction (and was already reverted once in the past) and since it provably isn't valid anymore (and I wasn't clear it ever functioned as expected) as the only backend to leverage the feature crashes transpile() this commit just opts to remove it as a potential breaking change. * Fix release note typos
Summary
This commit removes the "faulty qubits" support from the transpile(). Previously the transpile() function would attempt to filter out any faulty qubits or gates reported in a BackendV1's BackendProperties object and remap the qubits based on that. However, this code was never actually functioning as the first BackendV1 based backend to attempt to set these flags is causing an internal panic in rustworkx trying to created the remapped coupling map. This code path was mildly controversial at the time of introduction (and was already reverted once in the past) and since it provably isn't valid anymore (and I wasn't clear it ever functioned as expected) as the only backend to leverage the feature crashes transpile() this commit just opts to remove it as a potential breaking change.
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