Fix UnitarySynthesis pass bug when target contains global gates (Qiskit#13651)

* Confirm 2q basis gate candidates are in fact 2-qubit gates. Add test using target with global gates.

* Add reno

* Apply Matt's suggestion

Co-authored-by: Matthew Treinish <mtreinish@kortar.org>

* Add semicolon

* Apply Shelly's suggestion

---------

Co-authored-by: Matthew Treinish <mtreinish@kortar.org>

Author: ElePT

crates/accelerate/src/unitary_synthesis.rs

@@ -545,6 +545,7 @@ fn get_2q_decomposers_from_target(
     let mut available_2q_props: IndexMap<&str, (Option<f64>, Option<f64>)> = IndexMap::new();
 
     let mut qubit_gate_map = IndexMap::new();
+
     match target.operation_names_for_qargs(Some(&qubits)) {
         Ok(direct_keys) => {
             qubit_gate_map.insert(&qubits, direct_keys);
@@ -597,7 +598,10 @@ fn get_2q_decomposers_from_target(
                         OperationRef::Standard(_) => (),
                         _ => continue,
                     }
-
+                    // Filter out non-2q-gate candidates
+                    if op.operation.num_qubits() != 2 {
+                        continue;
+                    }
                     available_2q_basis.insert(key, replace_parametrized_gate(op.clone()));
 
                     if target.contains_key(key) {

releasenotes/notes/fix-unitary-synthesis-global-gates-19b93840b28cfcf7.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Fixed a bug in the :class:`.UnitarySynthesis` transpiler pass where 
+    non-2-qubit gates would be included in the available 2 qubit basis,
+    causing the ``TwoQubitWeylDecomposition`` to panic because of 
+    the dimension mismatch.

test/python/transpiler/test_unitary_synthesis.py

@@ -919,6 +919,21 @@ def test_3q_measure_all(self):
         self.assertIn("cx", ops)
         self.assertIn("measure", ops)
 
+    def test_target_with_global_gates(self):
+        """Test that 2q decomposition can handle a target with global gates."""
+
+        basis_gates = ["h", "p", "cp", "rz", "cx", "ccx", "swap"]
+        target = Target.from_configuration(basis_gates=basis_gates)
+
+        bell = QuantumCircuit(2)
+        bell.h(0)
+        bell.cx(0, 1)
+        bell_op = Operator(bell)
+        qc = QuantumCircuit(2)
+        qc.unitary(bell_op, [0, 1])
+        tqc = transpile(qc, target=target)
+        self.assertTrue(set(tqc.count_ops()).issubset(basis_gates))
+
 
 if __name__ == "__main__":
     unittest.main()