Adding global_phase gate in qiskit-terra

qiskit/circuit/library/__init__.py

@@ -124,6 +124,7 @@
    XGate
    YGate
    ZGate
+   GlobalPhaseGate
 
 Standard Directives
 ===================

qiskit/circuit/library/standard_gates/__init__.py

@@ -42,7 +42,7 @@
 from .x import MCXGate, MCXGrayCode, MCXRecursive, MCXVChain
 from .y import YGate, CYGate
 from .z import ZGate, CZGate, CCZGate
-
+from .global_phase import GlobalPhaseGate
 from .multi_control_rotation_gates import mcrx, mcry, mcrz
 
 
@@ -80,6 +80,7 @@ def get_standard_gate_name_mapping():
         CYGate(),
         CZGate(),
         CCZGate(),
+        GlobalPhaseGate(Parameter("ϴ")),
         HGate(),
         PhaseGate(Parameter("ϴ")),
         RCCXGate(),

qiskit/circuit/library/standard_gates/global_phase.py

@@ -0,0 +1,62 @@
+# This code is part of Qiskit.
+#
+# (C) Copyright IBM 2023.
+#
+# This code is licensed under the Apache License, Version 2.0. You may
+# obtain a copy of this license in the LICENSE.txt file in the root directory
+# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
+#
+# Any modifications or derivative works of this code must retain this
+# copyright notice, and modified files need to carry a notice indicating
+# that they have been altered from the originals.
+
+"""Global Phase Gate"""
+
+from typing import Optional
+import numpy
+from qiskit.circuit.gate import Gate
+from qiskit.circuit.quantumregister import QuantumRegister
+from qiskit.circuit.quantumcircuit import QuantumCircuit
+from qiskit.circuit.parameterexpression import ParameterValueType
+
+
+class GlobalPhaseGate(Gate):
+    r"""The global phase gate (:math:`e^{i\theta}`).
+
+    Can be applied to a :class:`~qiskit.circuit.QuantumCircuit`
+
+    **Mathamatical Representation:**
+
+    .. math::
+        \text{GlobalPhaseGate}\ =
+            \begin{pmatrix}
+                e^{i\theta}
+            \end{pmatrix}
+    """
+
+    def __init__(self, phase: ParameterValueType, label: Optional[str] = None):
+        """
+        Args:
+            phase: The value of phase it takes.
+            label: An optional label for the gate.
+        """
+        super().__init__("global_phase", 0, [phase], label=label)
+
+    def _define(self):
+
+        q = QuantumRegister(0, "q")
+        qc = QuantumCircuit(q, name=self.name, global_phase=self.params[0])
+
+        self.definition = qc
+
+    def inverse(self):
+        r"""Return inverted GLobalPhaseGate gate.
+
+        :math:`\text{GlobalPhaseGate}(\lambda){\dagger} = \text{GlobalPhaseGate}(-\lambda)`
+        """
+        return GlobalPhaseGate(-self.params[0])
+
+    def __array__(self, dtype=complex):
+        """Return a numpy.array for the global_phase gate."""
+        theta = self.params[0]
+        return numpy.array([[numpy.exp(1j * theta)]], dtype=dtype)

qiskit/quantum_info/operators/operator.py

@@ -345,7 +345,7 @@ def compose(self, other, qargs=None, front=False):
         tensor = np.reshape(self.data, self._op_shape.tensor_shape)
         mat = np.reshape(other.data, other._op_shape.tensor_shape)
         indices = [num_indices - 1 - qubit for qubit in qargs]
-        final_shape = [np.product(output_dims), np.product(input_dims)]
+        final_shape = [int(np.product(output_dims)), int(np.product(input_dims))]
         data = np.reshape(
             Operator._einsum_matmul(tensor, mat, indices, shift, right_mul), final_shape
         )

releasenotes/notes/add-global-phase-gate-b52c5b25ab8a3cf6.yaml

@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    Added :class:`.GlobalPhaseGate` which can be applied to add a global phase
+    on the :class:`.QuantumCircuit`.
+

test/python/circuit/test_extensions_standard.py

@@ -19,7 +19,6 @@
 import numpy as np
 from scipy.linalg import expm
 from ddt import data, ddt, unpack
-
 from qiskit import ClassicalRegister, QuantumCircuit, QuantumRegister, execute
 from qiskit.exceptions import QiskitError
 from qiskit.circuit.exceptions import CircuitError
@@ -36,11 +35,14 @@
     RZGate,
     XGate,
     YGate,
+    GlobalPhaseGate,
 )
 from qiskit import BasicAer
 from qiskit.quantum_info import Pauli
 from qiskit.quantum_info.operators.predicates import matrix_equal, is_unitary_matrix
 from qiskit.utils.optionals import HAS_TWEEDLEDUM
+from qiskit.quantum_info import Operator
+from qiskit import transpile
 
 
 class TestStandard1Q(QiskitTestCase):
@@ -851,6 +853,50 @@ def test_z_reg_inv(self):
         self.assertEqual(instruction_set[1].qubits, (self.qr[1],))
         self.assertEqual(instruction_set[2].operation.params, [])
 
+    def test_global_phase(self):
+        qc = self.circuit
+        qc.append(GlobalPhaseGate(0.1), [])
+        self.assertEqual(self.circuit[0].operation.name, "global_phase")
+        self.assertEqual(self.circuit[0].operation.params, [0.1])
+        self.assertEqual(self.circuit[0].qubits, ())
+
+    def test_global_phase_inv(self):
+        instruction_set = self.circuit.append(GlobalPhaseGate(0.1), []).inverse()
+        self.assertEqual(len(instruction_set), 1)
+        self.assertEqual(instruction_set[0].operation.params, [-0.1])
+
+    def test_global_phase_matrix(self):
+        """Test global_phase matrix."""
+        theta = 0.1
+        np.testing.assert_allclose(
+            np.array(GlobalPhaseGate(theta)),
+            np.array([[np.exp(1j * theta)]], dtype=complex),
+            atol=1e-7,
+        )
+
+    def test_global_phase_consistency(self):
+        """Tests compatibility of GlobalPhaseGate with QuantumCircuit.global_phase"""
+        theta = 0.1
+        qc1 = QuantumCircuit(0, global_phase=theta)
+        qc2 = QuantumCircuit(0)
+        qc2.append(GlobalPhaseGate(theta), [])
+        np.testing.assert_allclose(
+            Operator(qc1),
+            Operator(qc2),
+            atol=1e-7,
+        )
+
+    def test_transpile_global_phase_consistency(self):
+        """Tests compatibility of transpiled GlobalPhaseGate with QuantumCircuit.global_phase"""
+        qc1 = QuantumCircuit(0, global_phase=0.3)
+        qc2 = QuantumCircuit(0, global_phase=0.2)
+        qc2.append(GlobalPhaseGate(0.1), [])
+        np.testing.assert_allclose(
+            Operator(transpile(qc1, basis_gates=["u"])),
+            Operator(transpile(qc2, basis_gates=["u"])),
+            atol=1e-7,
+        )
+
 
 @ddt
 class TestStandard2Q(QiskitTestCase):
@@ -1375,7 +1421,6 @@ def test_to_matrix(self):
     def test_to_matrix_op(self):
         """test gates implementing to_matrix generate matrix which matches
         definition using Operator."""
-        from qiskit.quantum_info import Operator
         from qiskit.circuit.library.generalized_gates.gms import MSGate
         from qiskit.circuit.library.generalized_gates.pauli import PauliGate
         from qiskit.circuit.library.pauli_evolution import PauliEvolutionGate