Add VirtualZGate to native gateset

qiskit_ionq/__init__.py

@@ -35,7 +35,7 @@
     TrappedIonOptimizerPluginCommuteGpi2ThroughMs,
 )
 from .version import __version__
-from .ionq_gates import GPIGate, GPI2Gate, MSGate, ZZGate
+from .ionq_gates import GPIGate, GPI2Gate, VirtualZGate, MSGate, ZZGate
 from .constants import ErrorMitigation
 from .ionq_equivalence_library import add_equivalences
 
@@ -50,6 +50,7 @@
     "GPIGate",
     "GPI2Gate",
     "MSGate",
+    "VirtualZGate",
     "ZZGate",
     "ErrorMitigation",
     "add_equivalences",

qiskit_ionq/helpers.py

@@ -127,6 +127,7 @@
 ionq_native_basis_gates = [
     "gpi",
     "gpi2",
+    "gz",  # VirtualZ gate (RZ)
     "ms",  # Pairwise MS gate
     "zz",  # ZZ gate
 ]

qiskit_ionq/ionq_equivalence_library.py

@@ -38,7 +38,7 @@
     RZZGate,
     UGate,
 )
-from .ionq_gates import GPIGate, GPI2Gate, MSGate, ZZGate
+from .ionq_gates import GPIGate, GPI2Gate, VirtualZGate, MSGate, ZZGate
 
 
 # 1q gates
@@ -81,6 +81,15 @@ def gpi2_gate_equivalence() -> None:
     SessionEquivalenceLibrary.add_equivalence(GPI2Gate(phi), circ)
 
 
+def virtualz_gate_equivalence() -> None:
+    """VirtualZ(θ) -> RZ(θ) (for Aer/QIS simulation)."""
+    q = QuantumRegister(1, "q")
+    theta = Parameter("theta_param")
+    circ = QuantumCircuit(q)
+    circ.append(RZGate(theta), [0])
+    SessionEquivalenceLibrary.add_equivalence(VirtualZGate(theta), circ)
+
+
 # 2q native gates -> standard rotations (helps simulation & pattern matching)
 
 
@@ -126,6 +135,7 @@ def add_equivalences() -> None:
     u_gate_equivalence()
     gpi_gate_equivalence()
     gpi2_gate_equivalence()
+    virtualz_gate_equivalence()
     # 2q
     zz_gate_equivalence()
     # CX (both backends)

qiskit_ionq/ionq_gates.py

@@ -102,6 +102,43 @@ def __array__(self, dtype=None, copy=None):
         return arr
 
 
+class VirtualZGate(Gate):
+    r"""Single-qubit VirtualZ (GZ) gate.
+    **Circuit symbol:**
+    .. parsed-literal::
+             ┌───────┐
+        q_0: ┤ GZ(θ) ├
+             └───────┘
+    **Matrix Representation:**
+
+    .. math::
+
+        GZ(\theta) =
+            \begin{pmatrix}
+                e^{-i\theta/2} & 0 \\
+                0 & e^{i\theta/2}
+            \end{pmatrix}
+
+    Equivalent to RZ(θ).
+    """
+
+    def __init__(self, theta: ParameterValueType, label: Optional[str] = None):
+        """Create new VirtualZ gate."""
+        super().__init__("gz", 1, [theta], label=label)
+
+    def __array__(self, dtype=None, copy=None):
+        """Return a numpy array for the VirtualZ gate."""
+        theta = float(self.params[0])
+        arr = np.array(
+            [[np.exp(-1j * theta / 2), 0], [0, np.exp(1j * theta / 2)]]
+        )
+        if dtype is not None:
+            arr = arr.astype(dtype, copy=False)
+        if copy is True:
+            return arr.copy()
+        return arr
+
+
 class MSGate(Gate):
     r"""Entangling 2-Qubit MS gate.
     **Circuit symbol:**

test/helpers/test_qiskit_to_ionq.py

@@ -41,7 +41,7 @@
     compress_to_metadata_string,
     get_user_agent,
 )
-from qiskit_ionq.ionq_gates import GPIGate, GPI2Gate, MSGate, ZZGate
+from qiskit_ionq.ionq_gates import GPIGate, GPI2Gate, VirtualZGate, MSGate, ZZGate
 from qiskit_ionq.constants import ErrorMitigation
 
 
@@ -320,6 +320,7 @@ def test_native_circuit_transpile(simulator_backend):
     circ.append(GPIGate(0.1), [0])
     circ.append(GPI2Gate(0.2), [1])
     circ.append(MSGate(0.2, 0.3, 0.25), [1, 2])
+    circ.append(VirtualZGate(0.3), [0])
     circ.append(ZZGate(0.4), [0, 2])
 
     with pytest.raises(TranspilerError) as exc_info:
@@ -338,6 +339,7 @@ def test_full_native_circuit(simulator_backend):
     qc.append(GPIGate(0.1), [0])
     qc.append(GPI2Gate(0.2), [1])
     qc.append(MSGate(0.2, 0.3, 0.25), [1, 2])
+    qc.append(VirtualZGate(0.3), [0])
     qc.append(ZZGate(0.4), [0, 2])
     ionq_json = qiskit_to_ionq(
         qc,
@@ -378,6 +380,7 @@ def test_full_native_circuit(simulator_backend):
                 {"gate": "gpi", "target": 0, "phase": 0.1},
                 {"gate": "gpi2", "target": 1, "phase": 0.2},
                 {"gate": "ms", "targets": [1, 2], "phases": [0.2, 0.3], "angle": 0.25},
+                {"gate": "gz", "targets": [0], "phase": 0.3},
                 {"gate": "zz", "angle": 0.4, "targets": [0, 2]},
             ],
         },

test/ionq_gates/test_gates.py

@@ -31,8 +31,8 @@
 
 import pytest
 
-from qiskit.circuit.library import XGate, YGate, RXGate, RYGate, HGate
-from qiskit_ionq import GPIGate, GPI2Gate, MSGate, ZZGate
+from qiskit.circuit.library import XGate, YGate, RXGate, RYGate, RZGate, HGate
+from qiskit_ionq import GPIGate, GPI2Gate, VirtualZGate, MSGate, ZZGate
 
 
 @pytest.mark.parametrize("gate,phase", [(XGate(), 0), (YGate(), 0.25)])
@@ -97,6 +97,22 @@ def test_ms_inverse(params):
     np.testing.assert_array_almost_equal(mat.dot(mat.conj().T), np.identity(4))
 
 
+@pytest.mark.parametrize("theta", [0, 0.1, 0.4, np.pi / 2, np.pi, 2 * np.pi])
+def test_virtualz_equivalence(theta):
+    """Tests that VirtualZGate matches RZGate at various angles."""
+    gz_gate = VirtualZGate(theta)
+    rz_gate = RZGate(theta)
+    np.testing.assert_array_almost_equal(gz_gate.to_matrix(), rz_gate.to_matrix())
+
+
+@pytest.mark.parametrize("theta", [0, 0.1, 0.4, np.pi / 2, np.pi, 2 * np.pi])
+def test_gz_inverse(theta):
+    """Tests that the VirtualZ gate is unitary."""
+    gate = VirtualZGate(theta)
+    mat = np.array(gate)
+    np.testing.assert_array_almost_equal(mat.dot(mat.conj().T), np.identity(2))
+
+
 @pytest.mark.parametrize(
     "angle",
     [0, 0.1, 0.4, np.pi / 2, np.pi, 2 * np.pi],