Add native support for the SX gate (#158)

* Add SX support

* changelog

* SX inverse tests

CHANGELOG.md

@@ -6,6 +6,9 @@
 
 ### Improvements
 
+* Added support for the `qml.SX` operation to the Qiskit devices.
+  [(#158)](https://github.com/PennyLaneAI/pennylane-qiskit/pull/158)
+
 ### Documentation
 
 ### Bug fixes
@@ -14,6 +17,8 @@
 
 This release contains contributions from (in alphabetical order):
 
+Antal Száva
+
 ---
 
 # Release 0.18.0

pennylane_qiskit/qiskit_device.py

@@ -47,6 +47,7 @@
     "RZ": ex.RZGate,
     "S": ex.SGate,
     "T": ex.TGate,
+    "SX": ex.SXGate,
     # Adding the following for conversion compatibility
     "CSWAP": ex.CSwapGate,
     "CRX": ex.CRXGate,

tests/test_apply.py

@@ -42,7 +42,7 @@
 )
 
 
-single_qubit_operations = [qml.PauliX, qml.PauliY, qml.PauliZ, qml.Hadamard, qml.S, qml.T]
+single_qubit_operations = [qml.PauliX, qml.PauliY, qml.PauliZ, qml.Hadamard, qml.S, qml.T, qml.SX]
 
 single_qubit_operations_param = [qml.PhaseShift, qml.RX, qml.RY, qml.RZ]
 two_qubit = [qml.CNOT, qml.SWAP, qml.CZ]

tests/test_converter.py

@@ -476,12 +476,13 @@ def test_one_qubit_operations_supported_by_pennylane(self, recorder):
         qc.h(single_wire)
         qc.s(single_wire)
         qc.t(single_wire)
+        qc.sx(single_wire)
 
         quantum_circuit = load(qc)
         with recorder:
             quantum_circuit()
 
-        assert len(recorder.queue) == 6
+        assert len(recorder.queue) == 7
 
         assert recorder.queue[0].name == "PauliX"
         assert recorder.queue[0].parameters == []
@@ -507,6 +508,10 @@ def test_one_qubit_operations_supported_by_pennylane(self, recorder):
         assert recorder.queue[5].parameters == []
         assert recorder.queue[5].wires == Wires(single_wire)
 
+        assert recorder.queue[6].name == "SX"
+        assert recorder.queue[6].parameters == []
+        assert recorder.queue[6].wires == Wires(single_wire)
+
     def test_one_qubit_parametrized_operations_supported_by_pennylane(self, recorder):
         """Tests loading a circuit with the one-qubit parametrized operations supported by PennyLane."""
 

tests/test_inverses.py

@@ -22,6 +22,7 @@ class TestInverses:
             ("Hadamard", 0),
             ("S", 1),
             ("T", 1),
+            ("SX", 0)
         ],
     )
     def test_supported_gate_inverse_single_wire_no_parameters(self, name, expected_output):
@@ -253,3 +254,19 @@ def circuit():
             return qml.expval(qml.PauliX(0))
 
         assert np.allclose(circuit(), expected_output, atol=tol, rtol=0)
+
+    @pytest.mark.parametrize("par", [np.pi / i for i in range(1, 5)])
+    def test_sx_gate_inverses(self, par):
+        """Tests the inverse of the SX gate"""
+
+        dev = qml.device("qiskit.aer", method="statevector", wires=2, shots=None)
+
+        expected_output = math.sin(par)
+
+        @qml.qnode(dev)
+        def circuit():
+            qml.RY(par, wires=[0])
+            qml.SX(wires=[0]).inv()
+            return qml.expval(qml.PauliX(0))
+
+        assert np.allclose(circuit(), expected_output, atol=tol, rtol=0)