Fix an edge case in Sabre's release valve (backport #13114) #13130
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* Fix edge case in Sabre release valve If a Sabre trial does not find a set of Swaps to route nodes, the "release valve" adds Swaps to route the two-qubit gate in between the the closest two qubits. In rare cases, this leads to _more_ than one gate being routable, which was not handled correctly previously. Co-authored-by: Jake Lishman <jake.lishman@ibm.com> * add reno and test * Use sensible syntax Co-authored-by: Kevin Hartman <kevin@hart.mn> * Use sensible grammar Co-authored-by: Kevin Hartman <kevin@hart.mn> * clippy * Check if the new test breaks CI * Revert "Check if the new test breaks CI" This reverts commit 01bcdc7. --------- Co-authored-by: Jake Lishman <jake.lishman@ibm.com> Co-authored-by: Kevin Hartman <kevin@hart.mn> (cherry picked from commit f2ca920)
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Changelog: Bugfix
Pull Request Test Coverage Report for Build 10811797234Details
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Sep 11, 2024
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Summary
Fixes #13081.
Details and comments
If a Sabre trial does not find a set of Swaps to route nodes, the "release valve" adds Swaps to route the two-qubit gate in between the the closest two qubits. In rare cases, this leads to more than one gate being routable, which was not handled correctly previously.
As I understand it this should only ever occur if the release-valve adds a single swap and we have a scenario like
If more than one swap gate is applied it should not be possible that two gates are routable, so the code now only checks for a second routable gate if we insert a single swap. If someone can find a counterexample we can change the code to check for any routable gate after the release valve 🙂
This is an automatic backport of pull request #13114 done by Mergify.