redress global_phase in controlled UnitaryGate

qiskit/extensions/unitary.py

@@ -133,7 +133,7 @@ def control(self, num_ctrl_qubits=1, label=None, ctrl_state=None):
             QiskitError: Invalid ctrl_state.
             ExtensionError: Non-unitary controlled unitary.
         """
-        cmat = _compute_control_matrix(self.to_matrix(), num_ctrl_qubits, ctrl_state=ctrl_state)
+        cmat = _compute_control_matrix(self.to_matrix(), num_ctrl_qubits, ctrl_state=None)
         iso = isometry.Isometry(cmat, 0, 0)
         cunitary = ControlledGate('c-unitary', num_qubits=self.num_qubits+num_ctrl_qubits,
                                   params=[cmat], label=label, num_ctrl_qubits=num_ctrl_qubits,
@@ -147,9 +147,8 @@ def control(self, num_ctrl_qubits=1, label=None, ctrl_state=None):
             raise ExtensionError('controlled unitary generation failed')
         phase = numpy.angle(diag[0])
         if phase:
-            qreg = cunitary.definition.qregs[0]
-            cunitary.definition.u3(numpy.pi, phase, phase - numpy.pi, qreg[0])
-            cunitary.definition.u3(numpy.pi, 0, numpy.pi, qreg[0])
+            # need to apply to _definition since open controls creates temporary definition
+            cunitary._definition.global_phase = phase
         cunitary.base_gate = self.copy()
         cunitary.base_gate.label = self.label
         return cunitary

qiskit/transpiler/passes/synthesis/unitary_synthesis.py

@@ -84,7 +84,6 @@ def run(self, dag: DAGCircuit) -> DAGCircuit:
         Returns:
             Output dag with UnitaryGates synthesized to target basis.
         """
-
         euler_basis = _choose_euler_basis(self._basis_gates)
         kak_gate = _choose_kak_gate(self._basis_gates)
 

releasenotes/notes/fix-bug-in-controlled-unitary-when-setting-ctrl_state-2f9af3b9f0f7903f.yaml

@@ -0,0 +1,15 @@
+---
+issues:
+  - |
+    Previously, when creating decomposition of controlled unitary gate
+    using Isometry, global phase differences in the decomposition were
+    corrected by applying single qubit gates. This PR instead just
+    sets the global phase of the circuit definition to this phase
+    correction.
+fixes:
+  - |
+    Fixes a bug where setting ctrl_state of a `UnitaryGate` would
+    apparently have no effect. In reality it was happening twice; once
+    in the creation of the matrix for the controlled unitary and again
+    when calling the `definition` method of the `ControlledGate`
+    class.

test/python/circuit/test_controlled_gate.py

@@ -644,7 +644,7 @@ def test_controlled_random_unitary(self, num_ctrl_qubits):
         cop_mat = _compute_control_matrix(base_mat, num_ctrl_qubits)
         self.assertTrue(matrix_equal(cop_mat, test_op.data, ignore_phase=True))
 
-    @combine(num_ctrl_qubits=[1, 2, 3], ctrl_state=[None])
+    @combine(num_ctrl_qubits=[1, 2, 3], ctrl_state=[0, None])
     def test_open_controlled_unitary_z(self, num_ctrl_qubits, ctrl_state):
         """Test that UnitaryGate with control returns params."""
         umat = np.array([[1, 0], [0, -1]])
@@ -653,6 +653,17 @@ def test_open_controlled_unitary_z(self, num_ctrl_qubits, ctrl_state):
         ref_mat = _compute_control_matrix(umat, num_ctrl_qubits, ctrl_state=ctrl_state)
         self.assertEqual(Operator(cugate), Operator(ref_mat))
 
+    def test_controlled_controlled_unitary(self):
+        """Test that global phase in iso decomposition of unitary is handled."""
+        umat = np.array([[1, 0], [0, -1]])
+        ugate = UnitaryGate(umat)
+        cugate = ugate.control()
+        ccugate = cugate.control()
+        ccugate2 = ugate.control(2)
+        ref_mat = _compute_control_matrix(umat, 2)
+        self.assertTrue(Operator(ccugate2).equiv(Operator(ref_mat)))
+        self.assertTrue(Operator(ccugate).equiv(Operator(ccugate2)))
+
     @data(1, 2, 3)
     def test_open_controlled_unitary_matrix(self, num_ctrl_qubits):
         """test open controlled unitary matrix"""