Add H as an alias for Hadamard operator

doc/releases/changelog-dev.md

@@ -189,6 +189,9 @@
 
 <h4>Other Improvements</h4>
 
+* Added `qml.H` as an alias for the Hadamard operator.
+  [(#6450)](https://github.com/PennyLaneAI/pennylane/pull/6450)
+
 * Added `show_wire_labels` option to `draw` and `draw_mpl`, which hides wire labels when set to `False`.
   Defaults to `True`.
   [(#6410)](https://github.com/PennyLaneAI/pennylane/pull/6410)
@@ -496,5 +499,6 @@ Erick Ochoa Lopez,
 Lee J. O'Riordan,
 Mudit Pandey,
 Andrija Paurevic,
+Alex Preciado,
 Ashish Kanwar Singh,
 David Wierichs,

pennylane/devices/tests/test_gates.py

@@ -54,6 +54,7 @@
     "CH": qml.CH(wires=[0, 1]),
     "DiagonalQubitUnitary": qml.DiagonalQubitUnitary(np.array([1, 1]), wires=[0]),
     "Hadamard": qml.Hadamard(wires=[0]),
+    "H": qml.H(wires=[0]),
     "MultiRZ": qml.MultiRZ(0, wires=[0]),
     "PauliX": qml.X(0),
     "PauliY": qml.Y(0),
@@ -281,6 +282,7 @@ def adjoint_tuple(op, orig_mat):
     (qml.Y, Y),
     (qml.Z, Z),
     (qml.Hadamard, H),
+    (qml.H, H),
     (qml.S, S),
     (qml.T, T),
     (qml.SX, SX),

pennylane/devices/tests/test_measurements.py

@@ -38,6 +38,7 @@
 obs = {
     "Identity": qml.Identity(wires=[0]),
     "Hadamard": qml.Hadamard(wires=[0]),
+    "H": qml.H(wires=[0]),
     "Hermitian": qml.Hermitian(np.eye(2), wires=[0]),
     "PauliX": qml.PauliX(0),
     "PauliY": qml.PauliY(0),

pennylane/ops/qubit/__init__.py

@@ -46,6 +46,7 @@
     "Identity",
     "Snapshot",
     "Hadamard",
+    "H",
     "PauliX",
     "X",
     "PauliY",
@@ -106,6 +107,7 @@
 
 __obs__ = {
     "Hadamard",
+    "H",
     "PauliX",
     "X",
     "PauliY",

pennylane/ops/qubit/non_parametric_ops.py

@@ -39,6 +39,8 @@ class Hadamard(Observable, Operation):
 
     .. math:: H = \frac{1}{\sqrt{2}}\begin{bmatrix} 1 & 1\\ 1 & -1\end{bmatrix}.
 
+    .. seealso:: The equivalent short-form alias :class:`~H`
+
     **Details:**
 
     * Number of wires: 1
@@ -64,6 +66,17 @@ def label(
     ) -> str:
         return base_label or "H"
 
+    def __repr__(self) -> str:
+        """String representation."""
+        wire = self.wires[0]
+        if isinstance(wire, str):
+            return f"H('{wire}')"
+        return f"H({wire})"
+
+    @property
+    def name(self) -> str:
+        return "Hadamard"
+
     @staticmethod
     @lru_cache()
     def compute_matrix() -> np.ndarray:  # pylint: disable=arguments-differ
@@ -182,6 +195,24 @@ def pow(self, z: Union[int, float]):
         return super().pow(z % 2)
 
 
+H = Hadamard
+r"""H(wires)
+The Hadamard operator
+
+.. math:: H = \frac{1}{\sqrt{2}}\begin{bmatrix} 1 & 1\\ 1 & -1\end{bmatrix}.
+
+.. seealso:: The equivalent long-form alias :class:`~Hadamard`
+
+**Details:**
+
+* Number of wires: 1
+* Number of parameters: 0
+
+Args:
+    wires (Sequence[int] or int): the wire the operation acts on
+"""
+
+
 class PauliX(Observable, Operation):
     r"""
     The Pauli X operator

tests/circuit_graph/test_circuit_graph.py

@@ -322,7 +322,7 @@ def test_print_contents(self):
             circuit_w_wires.print_contents()
         out = f.getvalue().strip()
 
-        expected = """Operations\n==========\nHadamard(wires=[0])\nCNOT(wires=[0, 1])\n\nObservables\n===========\nsample(wires=[0, 1, 2])"""
+        expected = """Operations\n==========\nH(0)\nCNOT(wires=[0, 1])\n\nObservables\n===========\nsample(wires=[0, 1, 2])"""
         assert out == expected
 
     tape_depth = (

tests/ops/op_math/test_composite.py

@@ -38,7 +38,7 @@
 )
 
 ops_rep = (
-    "X(0) # Z(0) # Hadamard(wires=[0])",
+    "X(0) # Z(0) # H(0)",
     "(CNOT(wires=[0, 1])) # RX(1.23, wires=[1]) # I(0)",
     "IsingXX(4.56, wires=[2, 3]) # (Toffoli(wires=[1, 2, 3])) # Rot(0.34, 1.0, 0, wires=[0])",
 )

tests/ops/op_math/test_sprod.py

@@ -86,7 +86,7 @@
 ops_rep = (
     "1.0 * X(0)",
     "0.0 * Z(0)",
-    "1j * Hadamard(wires=[0])",
+    "1j * H(0)",
     "1.23 * CNOT(wires=[0, 1])",
     "4.56 * RX(1.23, wires=[1])",
     "(1+2j) * I(0)",

tests/ops/qubit/test_non_parametric_ops.py

@@ -68,18 +68,22 @@
 
 STRING_REPR = (
     (qml.Identity(0), "I(0)"),
+    (qml.Hadamard(0), "H(0)"),
     (qml.PauliX(0), "X(0)"),
     (qml.PauliY(0), "Y(0)"),
     (qml.PauliZ(0), "Z(0)"),
     (qml.Identity("a"), "I('a')"),
     (qml.Identity(10), "I(10)"),
     (qml.Identity(), "I()"),
+    (qml.Hadamard("a"), "H('a')"),
     (qml.PauliX("a"), "X('a')"),
     (qml.PauliY("a"), "Y('a')"),
     (qml.PauliZ("a"), "Z('a')"),
+    (qml.H("a"), "H('a')"),
     (qml.X("a"), "X('a')"),
     (qml.Y("a"), "Y('a')"),
     (qml.Z("a"), "Z('a')"),
+    (qml.H(0), "H(0)"),
     (qml.X(1), "X(1)"),
     (qml.Y(2), "Y(2)"),
     (qml.Z(3), "Z(3)"),
@@ -92,6 +96,7 @@ def test_alias_XYZI(wire):
     assert qml.PauliY(wire) == qml.Y(wire)
     assert qml.PauliZ(wire) == qml.Z(wire)
     assert qml.Identity(wire) == qml.I(wire)
+    assert qml.Hadamard(wire) == qml.H(wire)
 
 
 class TestOperations:
@@ -1288,3 +1293,23 @@ def test_Z_class_name(self):
 
         assert qml.Z(0).name == "PauliZ"
         assert qml.PauliZ(0).name == "PauliZ"
+
+
+class TestHadamardAlias:
+    def test_H_class_name(self):
+        """Test the class name of H is by default correct"""
+        assert qml.H.__name__ == "Hadamard"
+        assert qml.Hadamard.__name__ == "Hadamard"
+
+        assert qml.H(0).name == "Hadamard"
+        assert qml.Hadamard(0).name == "Hadamard"
+
+    def test_hadamard_alias(self):
+        """Test that qml.H is an alias for qml.Hadamard."""
+        # Verify that qml.H is the same as qml.Hadamard
+        assert qml.H is qml.Hadamard, "qml.H should be an alias for qml.Hadamard"
+
+        # Verify that an instance of qml.H is treated as qml.Hadamard
+        assert isinstance(
+            qml.H(0), qml.Hadamard
+        ), "qml.H(0) should create an instance of qml.Hadamard"