# Source code for pennylane.ops.qubit.attributes

```
# Copyright 2018-2021 Xanadu Quantum Technologies Inc.
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
# http://www.apache.org/licenses/LICENSE-2.0
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""
This file contains a number of attributes that may be held by operators,
and lists all operators satisfying those criteria.
"""
from inspect import isclass
from pennylane.operation import Operator, Tensor
[docs]class Attribute(set):
r"""Class to represent a set of operators with a certain attribute.
**Example**
Suppose we would like to store a list of which qubit operations are
Pauli operators. We can create a new ``Attribute``, ``pauli_ops``, like so,
listing which operations satisfy this property.
>>> pauli_ops = Attribute(["PauliX", "PauliZ"])
We can check either a string or an Operation for inclusion in this set:
>>> qml.X(0) in pauli_ops
True
>>> "Hadamard" in pauli_ops
False
We can also dynamically add operators to the sets at runtime, by passing
either a string, an operation class, or an operation itself. This is useful
for adding custom operations to the attributes such as
``composable_rotations`` and ``self_inverses`` that are used in compilation
transforms.
>>> pauli_ops.add("PauliY")
>>> pauli_ops
["PauliX", "PauliY", "PauliZ"]
"""
[docs] def add(self, obj):
"""Add an Operator to an attribute."""
if isinstance(obj, str):
return super().add(obj)
try:
if isinstance(obj, Operator):
return super().add(obj.name)
if isclass(obj):
if issubclass(obj, Operator):
return super().add(obj.__name__)
raise TypeError
except TypeError as e:
raise TypeError(
"Only an Operator or string representing an Operator can be added to an attribute."
) from e
def __contains__(self, obj):
"""Check if the attribute contains a given Operator."""
if isinstance(obj, str):
return super().__contains__(obj)
# Hotfix: return False for all tensors.
# Can be removed or updated when tensor class is
# improved.
if isinstance(obj, Tensor):
return False
if isinstance(obj, Operator):
return super().__contains__(obj.name)
if isclass(obj):
if issubclass(obj, Operator):
return super().__contains__(obj.__name__)
return False
composable_rotations = Attribute(
[
"RX",
"RY",
"RZ",
"PhaseShift",
"CRX",
"CRY",
"CRZ",
"ControlledPhaseShift",
"IsingXX",
"IsingYY",
"IsingZZ",
"Rot",
]
)
"""Attribute: Operations for which composing multiple copies of the operation results in an
addition (or alternative accumulation) of parameters.
For example, ``qml.RZ`` is a composable rotation. Applying ``qml.RZ(0.1,
wires=0)`` followed by ``qml.RZ(0.2, wires=0)`` is equivalent to performing
a single rotation ``qml.RZ(0.3, wires=0)``.
An example for an alternative accumulation is the ``qml.Rot`` gate: although the three
angles it takes do not fulfil the composable property, the gate implements a rotation around an
axis by an effective angle which does.
"""
has_unitary_generator = Attribute(
[
"RX",
"RY",
"RZ",
"MultiRZ",
"PauliRot",
"IsingXX",
"IsingYY",
"IsingZZ",
"SingleExcitationMinus",
"SingleExcitationPlus",
"DoubleExcitationMinus",
"DoubleExcitationPlus",
"PCPhase",
"GlobalPhase",
]
)
"""Attribute: Operations that are generated by a unitary operator.
For example, the generator of ``qml.RZ`` is Pauli :math:`Z` with a prefactor of
:math:`-1/2`, and Pauli :math:`Z` is unitary. Contrary, the generator of
``qml.PhaseShift`` is ``np.array([[0, 0], [0, 1]])`` with a prefactor of 1,
which is not unitary. This attribute is used for decompositions in algorithms
using the Hadamard test like ``qml.metric_tensor`` when used without
approximation.
"""
self_inverses = Attribute(
["Hadamard", "PauliX", "PauliY", "PauliZ", "CNOT", "CZ", "CY", "CH", "SWAP", "Toffoli", "CCZ"]
)
"""Attribute: Operations that are their own inverses."""
symmetric_over_all_wires = Attribute(
[
"CZ",
"CCZ",
"SWAP",
"IsingXX",
"Identity",
"ISWAP",
"SISWAP",
"SQISW",
"MultiRZ",
"IsingXY",
"IsingYY",
"IsingZZ",
"PSWAP",
]
)
"""Attribute: Operations that are the same if you exchange the order of wires.
For example, ``qml.CZ(wires=[0, 1])`` has the same effect as ``qml.CZ(wires=[1,
0])`` due to symmetry of the operation.
"""
symmetric_over_control_wires = Attribute(["CCZ", "Toffoli"])
"""Attribute: Controlled operations that are the same if you exchange the order of all but
the last (target) wire.
For example, ``qml.Toffoli(wires=[0, 1, 2])`` has the same effect as
``qml.Toffoli(wires=[1, 0, 2])``, but neither are the same as
``qml.Toffoli(wires=[0, 2, 1])``.
"""
diagonal_in_z_basis = Attribute(
[
"PauliZ",
"S",
"T",
"CZ",
"CCZ",
"DiagonalQubitUnitary",
"RZ",
"PhaseShift",
"PCPhase",
"ControlledPhaseShift",
"MultiRZ",
"CRZ",
"IsingZZ",
]
)
"""Attribute: Operations that are diagonal in the computational basis.
For such operations, the eigenvalues provide all necessary information to
construct the matrix representation in the computational basis.
Note: Currently all gates with this attribute need
to explicitly define an eigenvalue representation.
The reason is that if this method is missing, eigenvalues are computed from the matrix
representation using ``np.linalg.eigvals``, which fails for some tensor types that the matrix
may be cast in on backpropagation devices.
"""
supports_broadcasting = Attribute(
[
"QubitUnitary",
"ControlledQubitUnitary",
"DiagonalQubitUnitary",
"SpecialUnitary",
"RX",
"RY",
"RZ",
"PhaseShift",
"PCPhase",
"ControlledPhaseShift",
"Rot",
"MultiRZ",
"PauliRot",
"CRX",
"CRY",
"CRZ",
"CRot",
"U1",
"U2",
"U3",
"IsingXX",
"IsingYY",
"IsingZZ",
"IsingXY",
"SingleExcitation",
"SingleExcitationPlus",
"SingleExcitationMinus",
"DoubleExcitation",
"DoubleExcitationPlus",
"DoubleExcitationMinus",
"OrbitalRotation",
"FermionicSWAP",
"QubitStateVector",
"StatePrep",
"AmplitudeEmbedding",
"AngleEmbedding",
"IQPEmbedding",
"QAOAEmbedding",
]
)
"""Attribute: Operations that support parameter broadcasting.
For such operations, the input parameters are allowed to have a single leading additional
broadcasting dimension, creating the operation with a ``batch_size`` and leading to
broadcasted tapes when used in a ``QuantumTape``.
"""
```

_modules/pennylane/ops/qubit/attributes

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