fix global phase in initializer

qiskit/extensions/quantum_initializer/initializer.py

@@ -26,7 +26,7 @@
 from qiskit.circuit.library.standard_gates.h import HGate
 from qiskit.circuit.library.standard_gates.s import SGate, SdgGate
 from qiskit.circuit.library.standard_gates.ry import RYGate
-from qiskit.circuit.library.standard_gates.u1 import U1Gate
+from qiskit.circuit.library.standard_gates.rz import RZGate
 from qiskit.circuit.reset import Reset
 from qiskit.quantum_info import Statevector
 
@@ -198,13 +198,13 @@ def gates_to_uncompute(self):
                 add_last_cnot = False
 
             if np.linalg.norm(phis) != 0:
-                rz_mult = self._multiplex(U1Gate, phis, last_cnot=add_last_cnot)
+                rz_mult = self._multiplex(RZGate, phis, last_cnot=add_last_cnot)
                 circuit.append(rz_mult.to_instruction(), q[i:self.num_qubits])
 
             if np.linalg.norm(thetas) != 0:
                 ry_mult = self._multiplex(RYGate, thetas, last_cnot=add_last_cnot)
                 circuit.append(ry_mult.to_instruction().reverse_ops(), q[i:self.num_qubits])
-
+        circuit.global_phase -= np.angle(sum(remaining_param))
         return circuit
 
     @staticmethod

test/python/circuit/test_initializer.py

@@ -23,7 +23,7 @@
 from qiskit import ClassicalRegister
 from qiskit import transpile
 from qiskit import execute, assemble, BasicAer
-from qiskit.quantum_info import state_fidelity, Statevector
+from qiskit.quantum_info import state_fidelity, Statevector, Operator
 from qiskit.exceptions import QiskitError
 from qiskit.test import QiskitTestCase
 
@@ -367,6 +367,44 @@ def test_from_int(self):
         actual_sv = Statevector.from_instruction(qc)
         self.assertTrue(desired_sv == actual_sv)
 
+    def _remove_resets(self, circ):
+        circ.data = [tup for tup in circ.data if tup[0].name != 'reset']
+
+    def test_global_phase_random(self):
+        """Test global phase preservation with random state vectors"""
+        from qiskit.quantum_info.random import random_statevector
+        repeats = 5
+        for n_qubits in [1, 2, 4]:
+            for irep in range(repeats):
+                with self.subTest(i=f'{n_qubits}_{irep}'):
+                    dim = 2**n_qubits
+                    qr = QuantumRegister(n_qubits)
+                    initializer = QuantumCircuit(qr)
+                    target = random_statevector(dim)
+                    initializer.initialize(target, qr)
+                    uninit = initializer.data[0][0].definition
+                    self._remove_resets(uninit)
+                    disentangler = Operator(uninit.data[0][0])
+                    zero = Statevector.from_int(0, dim)
+                    evolve = zero @ disentangler
+                    self.assertEqual(target, evolve)
+
+    def test_global_phase_1q(self):
+        """Test global phase preservation with some simple 1q statevectors"""
+        target_list = [Statevector([1j, 0]), Statevector([0, 1j]),
+                       Statevector([1j/np.sqrt(2), 1j/np.sqrt(2)])]
+        n_qubits = 1
+        dim = 2**n_qubits
+        qr = QuantumRegister(n_qubits)
+        for target in target_list:
+            with self.subTest(i=target):
+                initializer = QuantumCircuit(qr)
+                initializer.initialize(target, qr)
+                disentangler = Operator(initializer.data[0][0].definition.data[1][0])
+                zero = Statevector.from_int(0, dim)
+                actual = zero @ disentangler
+                self.assertEqual(target, actual)
+
 
 class TestInstructionParam(QiskitTestCase):
     """Test conversion of numpy type parameters."""