Tests to check the CX count upper bound

test/python/circuit/test_controlled_gate.py

@@ -19,7 +19,7 @@
 from numpy import pi
 from ddt import ddt, data, unpack
 
-from qiskit import QuantumRegister, QuantumCircuit, execute, BasicAer, QiskitError
+from qiskit import QuantumRegister, QuantumCircuit, execute, BasicAer, QiskitError, transpile
 from qiskit.test import QiskitTestCase
 from qiskit.circuit import ControlledGate, Parameter, Gate
 from qiskit.circuit.exceptions import CircuitError
@@ -73,6 +73,7 @@
     C3SXGate,
     C4XGate,
     MCPhaseGate,
+    MCSU2Gate,
 )
 from qiskit.circuit._utils import _compute_control_matrix
 import qiskit.circuit.library.standard_gates as allGates
@@ -1269,6 +1270,85 @@ def test_control_zero_operand_gate(self, num_ctrl_qubits):
         target.flat[-1] = -1
         self.assertEqual(Operator(controlled), Operator(target))
 
+    @data(5, 10, 15)
+    def test_mcsu2_cx_count(self, num_ctrl_qubits):
+        """Test if the CX count of the multicontrolled SU(2) gate,
+        `MCSU2Gate`, is less than or equal to the upper bound."""
+
+        alpha = np.random.rand() + 1.j * np.random.rand()
+        beta = np.random.rand() + 1.j * np.random.rand()
+
+        length = np.linalg.norm([alpha, beta])
+        su2 = np.array([
+            [alpha, -np.conj(beta)],
+            [beta, np.conj(alpha)]
+        ]) / length
+
+        mcsu2 = MCSU2Gate(su2, num_ctrl_qubits)
+        qc = QuantumCircuit(mcsu2.num_qubits)
+
+        qc.append(mcsu2, list(range(mcsu2.num_qubits)))
+
+        tr_mcsu2 = transpile(qc, basis_gates=["u", "cx"])
+        cx_count = tr_mcsu2.count_ops()["cx"]
+
+        if mcsu2.num_qubits % 2:
+            # odd
+            self.assertLessEqual(cx_count, 20 * mcsu2.num_qubits - 38)
+        else:
+            # even
+            self.assertLessEqual(cx_count, 20 * mcsu2.num_qubits - 42)
+
+    @data(5, 10, 15)
+    def test_mcsu2_cx_count_main_diag_real(self, num_ctrl_qubits):
+        """Test if the CX count of the multicontrolled SU(2) gate
+        with real-valued primary diagonal elements is less than or equal
+        to the upper bound."""
+
+        alpha = np.random.rand()
+        beta = np.random.rand() + 1.j * np.random.rand()
+
+        length = np.linalg.norm([alpha, beta])
+        su2 = np.array([
+            [alpha, -np.conj(beta)],
+            [beta, np.conj(alpha)]
+        ]) / length
+
+        mcsu2 = MCSU2Gate(su2, num_ctrl_qubits)
+        qc = QuantumCircuit(mcsu2.num_qubits)
+
+        qc.append(mcsu2, list(range(mcsu2.num_qubits)))
+
+        tr_mcsu2 = transpile(qc, basis_gates=["u", "cx"])
+        cx_count = tr_mcsu2.count_ops()["cx"]
+
+        self.assertLessEqual(cx_count, 16 * mcsu2.num_qubits - 40)
+
+    @data(5, 10, 15)
+    def test_mcsu2_cx_count_off_diag_real(self, num_ctrl_qubits):
+        """Test if the CX count of the multicontrolled SU(2) gate
+        with real-valued off-diagonal elements is less than or equal
+        to the upper bound."""
+
+        alpha = np.random.rand() + 1.j * np.random.rand()
+        beta = np.random.rand()
+
+        length = np.linalg.norm([alpha, beta])
+        su2 = np.array([
+            [alpha, -np.conj(beta)],
+            [beta, np.conj(alpha)]
+        ]) / length
+
+        mcsu2 = MCSU2Gate(su2, num_ctrl_qubits)
+        qc = QuantumCircuit(mcsu2.num_qubits)
+
+        qc.append(mcsu2, list(range(mcsu2.num_qubits)))
+
+        tr_mcsu2 = transpile(qc, basis_gates=["u", "cx"])
+        cx_count = tr_mcsu2.count_ops()["cx"]
+
+        self.assertLessEqual(cx_count, 16 * mcsu2.num_qubits - 40)
+
 
 @ddt
 class TestOpenControlledToMatrix(QiskitTestCase):