Remove QubitStateVector class (#6525)

**Context:** Completing the deprecation cycle of `QubitStateVector`. **Description of the Change:** 1. Update `deprecations.rst` 2. Update `changelog-dev.md` 3. Remove all deprecated source code Also, updated CI to install *latest* `pennylane-qiskit` rather than stable. References found in, - Catalyst: PennyLaneAI/catalyst#1289 - Lightning: PennyLaneAI/pennylane-lightning#985 - AQT: PennyLaneAI/pennylane-aqt#77 - Qulacs: PennyLaneAI/pennylane-qulacs#83 - Qiskit: PennyLaneAI/pennylane-qiskit#601 - Cirq: PennyLaneAI/pennylane-cirq#203 No references found in, - QML [sc-77482] --------- Co-authored-by: Mudit Pandey <mudit.pandey@xanadu.ai>
PennyLaneAI · Nov 14, 2024 · 51c1436 · 51c1436
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diff --git a/.github/workflows/interface-unit-tests.yml b/.github/workflows/interface-unit-tests.yml
@@ -470,7 +470,8 @@ jobs:
       pytest_markers: external
       pytest_additional_args: --disable-opmath=${{ inputs.disable_new_opmath }} -W ${{ inputs.python_warning_level }} ${{ inputs.python_warning_level != 'default' && '--continue-on-collection-errors' || '' }}
       additional_pip_packages: |
-        pyzx matplotlib stim quimb mitiq pennylane-qiskit ply
+        pyzx matplotlib stim quimb mitiq ply
+        git+https://github.com/PennyLaneAI/pennylane-qiskit.git@master
         ${{ needs.default-dependency-versions.outputs.jax-version }}
         ${{ needs.default-dependency-versions.outputs.tensorflow-version }}
         ${{ inputs.additional_python_packages }}

diff --git a/doc/development/deprecations.rst b/doc/development/deprecations.rst
@@ -103,6 +103,12 @@ Completed deprecation cycles
   - Deprecated in v0.39
   - Removed in v0.40
 
+
+* The ``qml.QubitStateVector`` template has been removed. Instead, use :class:`~pennylane.StatePrep`.
+
+  - Deprecated in v0.39
+  - Removed in v0.40
+
 * ``qml.broadcast`` has been removed. Users should use ``for`` loops instead.
 
   - Deprecated in v0.39

diff --git a/doc/releases/changelog-dev.md b/doc/releases/changelog-dev.md
@@ -78,6 +78,9 @@
   process the diff method.
   [(#6535)](https://github.com/PennyLaneAI/pennylane/pull/6535)
 
+* The `qml.QubitStateVector` template has been removed. Instead, use `qml.StatePrep`.
+  [(#6525)](https://github.com/PennyLaneAI/pennylane/pull/6525)
+
 * `qml.broadcast` has been removed. Users should use `for` loops instead.
   [(#6527)](https://github.com/PennyLaneAI/pennylane/pull/6527)
 

diff --git a/pennylane/data/attributes/operator/operator.py b/pennylane/data/attributes/operator/operator.py
@@ -127,7 +127,6 @@ def supported_ops(cls) -> frozenset[Type[Operator]]:
                 qml.SpecialUnitary,
                 # pennylane/ops/state_preparation.py
                 qml.BasisState,
-                qml.QubitStateVector,
                 qml.StatePrep,
                 qml.QubitDensityMatrix,
                 # pennylane/ops/qutrit/matrix_obs.py

diff --git a/pennylane/devices/_qubit_device.py b/pennylane/devices/_qubit_device.py
@@ -1706,7 +1706,7 @@ def adjoint_jacobian(
                     )
                 ops = op.decomposition()
                 expanded_ops.extend(reversed(ops))
-            elif op.name not in ("StatePrep", "QubitStateVector", "BasisState", "Snapshot"):
+            elif op.name not in ("StatePrep", "BasisState", "Snapshot"):
                 expanded_ops.append(op)
 
         trainable_params = []

diff --git a/pennylane/devices/default_mixed.py b/pennylane/devices/default_mixed.py
@@ -96,7 +96,6 @@ class DefaultMixed(QubitDevice):
         "Identity",
         "Snapshot",
         "BasisState",
-        "QubitStateVector",
         "StatePrep",
         "QubitDensityMatrix",
         "QubitUnitary",

diff --git a/pennylane/devices/tests/test_gates.py b/pennylane/devices/tests/test_gates.py
@@ -68,7 +68,6 @@
     "CPhaseShift00": qml.CPhaseShift00(0, wires=[0, 1]),
     "CPhaseShift01": qml.CPhaseShift01(0, wires=[0, 1]),
     "CPhaseShift10": qml.CPhaseShift10(0, wires=[0, 1]),
-    "QubitStateVector": qml.QubitStateVector(np.array([1.0, 0.0]), wires=[0]),
     "StatePrep": qml.StatePrep(np.array([1.0, 0.0]), wires=[0]),
     "QubitDensityMatrix": qml.QubitDensityMatrix(np.array([[0.5, 0.0], [0, 0.5]]), wires=[0]),
     "QubitUnitary": qml.QubitUnitary(np.eye(2), wires=[0]),

diff --git a/pennylane/ops/functions/is_commuting.py b/pennylane/ops/functions/is_commuting.py
@@ -262,7 +262,6 @@ def check_commutation_two_non_simplified_rotations(operation1, operation2):
 ]
 non_commuting_operations = [
     # StatePrepBase
-    "QubitStateVector",
     "StatePrep",
     "BasisState",
     # Templates

diff --git a/pennylane/ops/qubit/__init__.py b/pennylane/ops/qubit/__init__.py
@@ -82,7 +82,6 @@
     "IsingXY",
     "BasisState",
     "StatePrep",
-    "QubitStateVector",
     "QubitDensityMatrix",
     "QubitUnitary",
     "BlockEncode",

diff --git a/pennylane/ops/qubit/attributes.py b/pennylane/ops/qubit/attributes.py
@@ -247,7 +247,6 @@ def __contains__(self, obj):
         "DoubleExcitationMinus",
         "OrbitalRotation",
         "FermionicSWAP",
-        "QubitStateVector",
         "StatePrep",
         "AmplitudeEmbedding",
         "AngleEmbedding",

diff --git a/pennylane/ops/qubit/state_preparation.py b/pennylane/ops/qubit/state_preparation.py
@@ -15,8 +15,6 @@
 This submodule contains the discrete-variable quantum operations concerned
 with preparing a certain state on the device.
 """
-import warnings
-
 # pylint:disable=too-many-branches,abstract-method,arguments-differ,protected-access,no-member
 from typing import Optional
 
@@ -443,21 +441,6 @@ def _preprocess(state, wires, pad_with, normalize, validate_norm):
         return state
 
 
-class QubitStateVector(StatePrep):
-    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):
     r"""QubitDensityMatrix(state, wires)
     Prepare subsystems using the given density matrix.

diff --git a/tests/default_qubit_legacy.py b/tests/default_qubit_legacy.py
@@ -115,7 +115,6 @@ class DefaultQubitLegacy(QubitDevice):
         "Snapshot",
         "BasisState",
         "StatePrep",
-        "QubitStateVector",
         "QubitUnitary",
         "ControlledQubitUnitary",
         "BlockEncode",

diff --git a/tests/ops/functions/conftest.py b/tests/ops/functions/conftest.py
@@ -147,7 +147,7 @@
     PowOpObs,
     PowOperation,
     PowObs,
-    qml.QubitStateVector,
+    qml.StatePrep,
 }
 """Types that should not have actual instances created."""
 

diff --git a/tests/ops/qubit/test_attributes.py b/tests/ops/qubit/test_attributes.py
@@ -137,7 +137,6 @@ def test_tensor_check(self):
     "SpecialUnitary",
     "PauliRot",
     "MultiRZ",
-    "QubitStateVector",
     "StatePrep",
     "AmplitudeEmbedding",
     "AngleEmbedding",

diff --git a/tests/ops/qubit/test_state_prep.py b/tests/ops/qubit/test_state_prep.py
@@ -36,12 +36,6 @@ 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",
     [