Fix UGate docstring note about the OpenQASM 3 U definition (backport #16553) - #16774
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* Fix UGate docstring note about the OpenQASM 3 U definition The docstring claimed the matrix shown for UGate is the same as the built-in U gate in the OpenQASM 3.0 specification. The current specification defines U with an extra global phase: its matrix is exp(i*theta/2) times the matrix shown here. Update the note to state the relationship correctly, keeping the existing statement about the OpenQASM 2.0 global-phase difference. Fixes #15830 * Correct the global phase difference --------- Co-authored-by: Julien Gacon <gaconju@gmail.com> (cherry picked from commit bf915f4)
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Aug 14, 2026
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Summary
Fixes #15830.
The$e^{i\theta/2}$ , so the note now states the phase difference instead, using the wording suggested in the issue thread. The existing statement about the OpenQASM 2.0 phase difference is kept, since it is still correct relative to Qiskit's matrix.
UGatedocstring says its matrix is the same as the built-inUgate in the OpenQASM 3.0 specification. The current spec definesU(θ, φ, λ)as that matrix multiplied by a global phaseDetails and comments
Verified numerically: for 200 random angle triples, the spec's matrix $\tfrac{1}{2}\begin{pmatrix}1+e^{i\theta} & -ie^{i\lambda}(1-e^{i\theta})\ ie^{i\phi}(1-e^{i\theta}) & e^{i(\phi+\lambda)}(1+e^{i\theta})\end{pmatrix}$ equals$e^{i\theta/2}$ times $U_{\text{Qiskit}} = e^{i(\phi+\lambda)/2} U_{\text{OQ2}}$ also holds. Docs-only change, so no release note.
Operator(UGate(θ, φ, λ)), and the OpenQASM 2.0 relationAI disclosure: this PR was prepared with the assistance of Claude Code (Anthropic's Claude); I review and test all changes.
This is an automatic backport of pull request #16553 done by Mergify.