Fix ElidePermutations pass in the presence of PermutationGates (Qiskit#14603) (Qiskit#14622)

* fixing ElidePermutations and adding tests

* release notes

(cherry picked from commit 96fda18)

Co-authored-by: Alexander Ivrii <[email protected]>

Author: mergify[bot]

crates/accelerate/src/elide_permutations.rs

@@ -58,17 +58,13 @@ fn run(py: Python, dag: &mut DAGCircuit) -> PyResult<Option<(DAGCircuit, Vec<usi
                             .map(|q| q.index())
                             .collect();
 
-                        let remapped_qindices: Vec<usize> = (0..qindices.len())
-                            .map(|i| pattern[i])
-                            .map(|i| qindices[i as usize])
+                        let new_values: Vec<usize> = (0..qindices.len())
+                            .map(|i| mapping[qindices[pattern[i] as usize]])
                             .collect();
 
-                        qindices
-                            .iter()
-                            .zip(remapped_qindices.iter())
-                            .for_each(|(old, new)| {
-                                mapping[*old] = *new;
-                            });
+                        for i in 0..qindices.len() {
+                            mapping[qindices[i]] = new_values[i];
+                        }
                     } else {
                         unreachable!();
                     }

releasenotes/notes/fix-elide-permutation-gates-e4d2a718e1d50afa.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Fixed a bug in the :class:`.ElidePermutation` transpiler pass, where
+    the qubit mapping was not updated correctly in the presence of
+    :class:`.PermutationGate`\s, leading to incorrect circuits and
+    updates to the pass manager's property set.

test/python/transpiler/test_elide_permutations.py

@@ -12,6 +12,7 @@
 
 """Test ElidePermutations pass"""
 
+import itertools
 import unittest
 
 from qiskit.circuit.quantumcircuit import QuantumCircuit
@@ -20,6 +21,7 @@
 from qiskit.transpiler.passes.routing import StarPreRouting
 from qiskit.circuit.controlflow import IfElseOp
 from qiskit.quantum_info import Operator
+from qiskit.transpiler.passmanager import PassManager
 from qiskit.transpiler.coupling import CouplingMap
 from qiskit.transpiler.preset_passmanagers import generate_preset_pass_manager
 from test import QiskitTestCase  # pylint: disable=wrong-import-order
@@ -377,6 +379,20 @@ def test_unitary_equivalence(self):
             res = spm.run(qc)
             self.assertTrue(Operator.from_circuit(res).equiv(Operator(qc)))
 
+    def test_unitary_equivalence_permutation_gates(self):
+        """Test unitary equivalence of the original and transpiled circuits."""
+
+        for perm in itertools.permutations([0, 1, 2]):
+            qc = QuantumCircuit(5)
+            qc.h(1)
+            qc.swap(1, 2)
+            qc.swap(4, 3)
+            qc.append(PermutationGate(perm), [1, 2, 3])
+
+            pm = PassManager([ElidePermutations()])
+            res = pm.run(qc)
+            self.assertEqual(Operator.from_circuit(res), (Operator(qc)))
+
     def test_unitary_equivalence_routing_and_basis_translation(self):
         """Test on a larger example that includes routing and basis translation."""