Deprecate basis state preparation

doc/development/deprecations.rst

@@ -45,6 +45,20 @@ Pending deprecations
   - Deprecated in v0.39
   - Will be removed in v0.40
 
+* The ``decomp_depth`` argument in ``qml.device`` is deprecated. 
+
+  - Deprecated in v0.38
+  - Will be removed in v0.39
+
+* The ``simplify`` argument in ``qml.Hamiltonian`` and ``qml.ops.LinearCombination`` is deprecated. 
+  Instead, ``qml.simplify()`` can be called on the constructed operator.
+
+  - Deprecated in v0.37
+  - Will be removed in v0.39
+
+* The :class:`~pennylane.BasisStatePreparation` template is deprecated.
+  Instead, use :class:`~pennylane.BasisState`.
+
 * The ``QubitStateVector`` template is deprecated.
   Instead, use ``StatePrep``.
 

doc/releases/changelog-dev.md

@@ -104,6 +104,10 @@
 
 <h3>Deprecations 👋</h3>
 
+* The `qml.BasisStatePreparation` template is deprecated.
+  Instead, use `qml.BasisState`.
+  [(#6021)](https://github.com/PennyLaneAI/pennylane/pull/6021)
+
 * The `'ancilla'` argument for `qml.iterative_qpe` has been deprecated. Instead, use the `'aux_wire'` argument.
   [(#6277)](https://github.com/PennyLaneAI/pennylane/pull/6277)
 

pennylane/devices/tests/test_templates.py

@@ -225,6 +225,9 @@ def circuit():
             [math.fidelity_statevector(circuit(), exp_state)], [1.0], atol=tol(dev.shots)
         )
 
+    @pytest.mark.filterwarnings(
+        "ignore:BasisStatePreparation is deprecated:pennylane.PennyLaneDeprecationWarning"
+    )
     def test_BasisStatePreparation(self, device, tol):
         """Test the BasisStatePreparation template."""
         dev = device(4)

pennylane/templates/state_preparations/basis.py

@@ -15,6 +15,8 @@
 Contains the BasisStatePreparation template.
 """
 
+import warnings
+
 import numpy as np
 
 import pennylane as qml
@@ -30,6 +32,8 @@ class BasisStatePreparation(Operation):
         ``basis_state`` influences the circuit architecture and is therefore incompatible with
         gradient computations.
 
+        ``BasisStatePreparation`` is deprecated and will be removed in version 0.40. Instead, please use ``BasisState``.
+
     Args:
         basis_state (array): Input array of shape ``(n,)``, where n is the number of wires
             the state preparation acts on.
@@ -59,6 +63,13 @@ def circuit(basis_state):
     ndim_params = (1,)
 
     def __init__(self, basis_state, wires, id=None):
+
+        warnings.warn(
+            "BasisStatePreparation is deprecated and will be removed in version 0.40. "
+            "Instead, please use BasisState.",
+            qml.PennyLaneDeprecationWarning,
+        )
+
         basis_state = qml.math.stack(basis_state)
 
         # check if the `basis_state` param is batched

tests/capture/test_templates.py

@@ -27,8 +27,12 @@
 jax = pytest.importorskip("jax")
 jnp = jax.numpy
 
-pytestmark = pytest.mark.jax
-
+pytestmark = [
+    pytest.mark.jax,
+    pytest.mark.filterwarnings(
+        "ignore:BasisStatePreparation is deprecated:pennylane.PennyLaneDeprecationWarning"
+    ),
+]
 original_op_bind_code = qml.operation.Operator._primitive_bind_call.__code__
 
 

tests/templates/test_state_preparations/test_basis_state_prep.py

@@ -21,6 +21,10 @@
 
 import pennylane as qml
 
+pytestmark = pytest.mark.filterwarnings(
+    "ignore:BasisStatePreparation is deprecated:pennylane.PennyLaneDeprecationWarning"
+)
+
 
 def test_standard_validity():
     """Check the operation using the assert_valid function."""
@@ -33,6 +37,12 @@ def test_standard_validity():
     qml.ops.functions.assert_valid(op)
 
 
+def test_BasisStatePreparation_is_deprecated():
+    """Test that BasisStatePreparation is deprecated."""
+    with pytest.warns(qml.PennyLaneDeprecationWarning, match="BasisStatePreparation is deprecated"):
+        _ = qml.BasisStatePreparation([1, 0], wires=[0, 1])
+
+
 class TestDecomposition:
     """Tests that the template defines the correct decomposition."""
 

tests/test_qnode.py

@@ -975,15 +975,15 @@ def test_sampling_with_mcm(self, basis_state, mocker):
         @qml.qnode(dev)
         def cry_qnode(x):
             """QNode where we apply a controlled Y-rotation."""
-            qml.BasisStatePreparation(basis_state, wires=[0, 1])
+            qml.BasisState(basis_state, wires=[0, 1])
             qml.CRY(x, wires=[0, 1])
             return qml.sample(qml.PauliZ(1))
 
         @qml.qnode(dev)
         def conditional_ry_qnode(x):
             """QNode where the defer measurements transform is applied by
             default under the hood."""
-            qml.BasisStatePreparation(basis_state, wires=[0, 1])
+            qml.BasisState(basis_state, wires=[0, 1])
             m_0 = qml.measure(0)
             qml.cond(m_0, qml.RY)(x, wires=1)
             return qml.sample(qml.PauliZ(1))

tests/test_qnode_legacy.py

@@ -890,15 +890,15 @@ def test_sampling_with_mcm(self, basis_state, mocker):
         @qml.qnode(dev)
         def cry_qnode(x):
             """QNode where we apply a controlled Y-rotation."""
-            qml.BasisStatePreparation(basis_state, wires=[0, 1])
+            qml.BasisState(basis_state, wires=[0, 1])
             qml.CRY(x, wires=[0, 1])
             return qml.sample(qml.PauliZ(1))
 
         @qml.qnode(dev)
         def conditional_ry_qnode(x):
             """QNode where the defer measurements transform is applied by
             default under the hood."""
-            qml.BasisStatePreparation(basis_state, wires=[0, 1])
+            qml.BasisState(basis_state, wires=[0, 1])
             m_0 = qml.measure(0)
             qml.cond(m_0, qml.RY)(x, wires=1)
             return qml.sample(qml.PauliZ(1))

tests/transforms/test_batch_input.py

@@ -200,6 +200,9 @@ def circuit2(data, weights):
     assert np.allclose(res, indiv_res)
 
 
+@pytest.mark.filterwarnings(
+    "ignore:BasisStatePreparation is deprecated:pennylane.PennyLaneDeprecationWarning"
+)
 def test_basis_state_preparation(mocker):
     """Test that batching works for BasisStatePreparation"""
     dev = qml.device("default.qubit", wires=3)

tests/transforms/test_batch_params.py

@@ -174,6 +174,9 @@ def circuit2(data, weights):
     assert np.allclose(res, indiv_res)
 
 
+@pytest.mark.filterwarnings(
+    "ignore:BasisStatePreparation is deprecated:pennylane.PennyLaneDeprecationWarning"
+)
 def test_basis_state_preparation(mocker):
     """Test that batching works for BasisStatePreparation"""
     dev = qml.device("default.qubit", wires=4)

tests/transforms/test_defer_measurements.py

@@ -1347,6 +1347,9 @@ def quantum_control_circuit(rads):
 class TestTemplates:
     """Tests templates being conditioned on mid-circuit measurement outcomes."""
 
+    @pytest.mark.filterwarnings(
+        "ignore:BasisStatePreparation is deprecated:pennylane.PennyLaneDeprecationWarning"
+    )
     def test_basis_state_prep(self):
         """Test the basis state prep template conditioned on mid-circuit
         measurement outcomes."""