Add inverse method to ECRGate (Qiskit#9733)

* add inverse method to ECRGate * add release notes * Fix sphinx tags * Recategorise as bugfix --------- Co-authored-by: Julien Gacon <gaconju@gmail.com> Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com> Co-authored-by: Jake Lishman <jake.lishman@ibm.com>
comp-quantica · Mar 6, 2023 · 80ca1f3 · 80ca1f3
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diff --git a/qiskit/circuit/library/standard_gates/ecr.py b/qiskit/circuit/library/standard_gates/ecr.py
@@ -103,6 +103,10 @@ def _define(self):
 
         self.definition = qc
 
+    def inverse(self):
+        """Return inverse ECR gate (itself)."""
+        return ECRGate()  # self-inverse
+
     def to_matrix(self):
         """Return a numpy.array for the ECR gate."""
         return (

diff --git a/releasenotes/notes/add-inverse-ecr-e03720252a0c9c1e.yaml b/releasenotes/notes/add-inverse-ecr-e03720252a0c9c1e.yaml
@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    The method :meth:`.ECRGate.inverse` now returns another :class:`.ECRGate` instance
+    rather than a custom gate, since it is self inverse.