Qiskit / qiskit / 36404217175

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Commit Message

Leave unitaries unchanged when UnitarySynthesis has no basis or target (#16944)

* Fix empty UnitarySynthesis basis defaulting to [u, cx] (#16688)

* Polish empty-basis UnitarySynthesis fallback for #16688

Tighten the [u, cx] default so empty Target() still falls back, strengthen regression assertions for the issue repro, and clean up Rust comments/lints and the release note ahead of opening a PR.

* Limit [u, cx] fallback to no-target UnitarySynthesis cases

Keep empty Target()/preset no-constraints behavior so transpile(basis_gates=None) still preserves UnitaryGate. Remove the Rust-wide empty-basis default; retain the vacuous Clifford+T guard.

Co-authored-by: Cursor <cursoragent@cursor.com>

* Leave empty-basis UnitarySynthesis unchanged (#16688)

Drop the [u, cx] default and keep the nonempty Clifford+T guard so
UnitarySynthesis() without basis_gates/target no longer routes through
Solovay-Kitaev or invents a basis; unitaries stay as-is.

Co-authored-by: Cursor <cursoragent@cursor.com>

* Update crates/transpiler/src/passes/unitary_synthesis/decomposers.rs

Co-authored-by: Alexander Ivrii <alexi@il.ibm.com>

* Update releasenotes/notes/fix-empty-basis-unitary-synthesis-16688.yaml

Co-authored-by: Alexander Ivrii <alexi@il.ibm.com>

* Remove redundant empty-basis UnitarySynthesis regression test

Drop test_empty_basis_gates_leaves_unitary; test_empty_basis_gates already covers the leave-alone behavior.

Co-authored-by: Cursor <cursoragent@cursor.com>

* Tighten empty-basis UnitarySynthesis test to require operator equality

Use Operator equality instead of equiv in test_empty_basis_gates, since
leave-alone behavior should preserve the circuit exactly, not only up to
global phase.

Co-authored-by: Cursor <cursoragent@cursor.com>

---------

Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: Alexander Ivrii <alexi@il.ibm.com>

Coverage Stats

2 of 2 new or added lines in 1 file covered. (100.0%)

21 existing lines in 4 files now uncovered.

122350 of 138882 relevant lines covered (88.1%)

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