Deprecation QubitStateVector

doc/development/deprecations.rst

@@ -85,6 +85,12 @@ Pending deprecations
   - Deprecated in v0.37
   - Will be removed in v0.39
 
+* The ``QubitStateVector`` template is deprecated.
+  Instead, use ``StatePrep``.
+
+  - Deprecated in v0.39
+  - Will be removed in v0.40
+
 New operator arithmetic deprecations
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

doc/releases/changelog-dev.md

@@ -10,6 +10,10 @@
 
 <h3>Deprecations 👋</h3>
 
+* The ``QubitStateVector`` template is deprecated.
+   Instead, use ``StatePrep``.
+   [(#6172)](https://github.com/PennyLaneAI/pennylane/pull/6172)
+
 <h3>Documentation 📝</h3>
 
 <h3>Bug fixes 🐛</h3>
@@ -21,4 +25,5 @@
 
 This release contains contributions from (in alphabetical order):
 
+Guillermo Alonso
 Jack Brown

pennylane/ops/qubit/state_preparation.py

@@ -18,6 +18,8 @@
 # pylint:disable=too-many-branches,abstract-method,arguments-differ,protected-access,no-member
 from typing import Optional
 
+import warnings
+
 import numpy as np
 
 import pennylane as qml
@@ -386,9 +388,19 @@ def _preprocess(state, wires, pad_with, normalize, validate_norm):
         return state
 
 
-# pylint: disable=missing-class-docstring
 class QubitStateVector(StatePrep):
-    pass  # QSV is still available
+    r"""
+    ``QubitStateVector`` is deprecated and will be removed in version 0.40. Instead, please use ``StatePrep``.
+    """
+
+    # pylint: disable=too-many-arguments
+    def __init__(self, state, wires, pad_with=None, normalize=False, validate_norm=True):
+        warnings.warn(
+            "QubitStateVector is deprecated and will be removed in version 0.40. "
+            "Instead, please use StatePrep.",
+            qml.PennyLaneDeprecationWarning,
+        )
+        super().__init__(state, wires, pad_with, normalize, validate_norm)
 
 
 class QubitDensityMatrix(Operation):

tests/drawer/test_drawable_layers.py

@@ -196,7 +196,7 @@ def test_mid_measure_custom_wires(self):
         m1 = qml.measurements.MeasurementValue([mp1], lambda v: v)
 
         def teleport(state):
-            qml.QubitStateVector(state, wires=["A"])
+            qml.StatePrep(state, wires=["A"])
             qml.Hadamard(wires="a")
             qml.CNOT(wires=["a", "B"])
             qml.CNOT(wires=["A", "a"])

tests/ops/functions/conftest.py

@@ -38,7 +38,6 @@
     qml.sum(qml.X(0), qml.X(0), qml.Z(0), qml.Z(0)),
     qml.BasisState([1], wires=[0]),
     qml.ControlledQubitUnitary(np.eye(2), control_wires=1, wires=0),
-    qml.QubitStateVector([0, 1], wires=0),
     qml.QubitChannel([np.array([[1, 0], [0, 0.8]]), np.array([[0, 0.6], [0, 0]])], wires=0),
     qml.MultiControlledX(wires=[0, 1]),
     qml.Projector([1], 0),  # the state-vector version is already tested

tests/ops/functions/test_assert_valid.py

@@ -342,7 +342,11 @@ def create_op_instance(c, str_wires=False):
     if dim == 0:
         params = [1] * len(ndim_params)
     elif dim == 1:
-        params = [[1] * 2**n_wires] * len(ndim_params)
+
+        if c == qml.QubitStateVector:
+            params = [[1] + [0] * (2**n_wires - 1)] * len(ndim_params)
+        else:
+            params = [[1] * 2**n_wires] * len(ndim_params)
     elif dim == 2:
         params = [np.eye(2)] * len(ndim_params)
     else:
@@ -352,6 +356,12 @@ def create_op_instance(c, str_wires=False):
 
 
 @pytest.mark.jax
+@pytest.fixture(scope="function", autouse=True)
+def capture_warnings(recwarn):
+    """Capture warnings."""
+    yield
+
+
 @pytest.mark.parametrize("str_wires", (True, False))
 def test_generated_list_of_ops(class_to_validate, str_wires):
     """Test every auto-generated operator instance."""
@@ -390,4 +400,5 @@ def test_explicit_list_of_failing_ops(invalid_instance_and_error):
     """Test instances of ops that fail validation."""
     op, exc_type = invalid_instance_and_error
     with pytest.raises(exc_type):
+        print(op)
         assert_valid(op)

tests/ops/qubit/test_attributes.py

@@ -151,6 +151,15 @@ class TestSupportsBroadcasting:
     """Test that all operations in the ``supports_broadcasting`` attribute
     actually support broadcasting."""
 
+    @pytest.fixture(scope="function", autouse=False)
+    def capture_warnings(self, recwarn):
+        """Capture warnings."""
+        yield
+        if len(recwarn) > 0:
+            for w in recwarn:
+                assert isinstance(w.message, qml.PennyLaneDeprecationWarning)
+                assert "QubitStateVector is deprecated" in str(w.message)
+
     def test_all_marked_operations_are_tested(self):
         """Test that the subsets of the ``supports_broadcasting`` attribute
         defined above cover the entire attribute."""

tests/ops/qubit/test_state_prep.py

@@ -36,6 +36,12 @@ def test_adjoint_error_exception(op):
         op.adjoint()
 
 
+def test_QubitStateVector_is_deprecated():
+    """Test that QubitStateVector is deprecated."""
+    with pytest.warns(qml.PennyLaneDeprecationWarning, match="QubitStateVector is deprecated"):
+        _ = qml.QubitStateVector([1, 0, 0, 0], wires=[0, 1])
+
+
 @pytest.mark.parametrize(
     "op, mat, base",
     [