Source code for pennylane.ops.op_math.control

# 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.
"""
Contains the control transform.
"""
from functools import wraps

import pennylane as qml

from pennylane.operation import Operator
from pennylane.ops.op_math import Controlled


[docs]def ctrl(op, control, control_values=None, work_wires=None): """Create a method that applies a controlled version of the provided op. Args: op (function or :class:`~.operation.Operator`): A single operator or a function that applies pennylane operators. control (Wires): The control wire(s). control_values (bool or list[bool]): The value(s) the control wire(s) should take. Integers other than 0 or 1 will be treated as ``int(bool(x))``. work_wires (Any): Any auxiliary wires that can be used in the decomposition Returns: (function or :class:`~.operation.Operator`): If an Operator is provided, returns a Contolled version of the Operator. If a function is provided, returns a function with the same call signature that creates a controlled version of the provided function. .. seealso:: :class:`~.Controlled`. **Example** .. code-block:: python3 @qml.qnode(qml.device('default.qubit', wires=range(4))) def circuit(x): qml.PauliX(2) qml.ctrl(qml.RX, (1,2,3), control_values=(0,1,0))(x, wires=0) return qml.expval(qml.PauliZ(0)) >>> print(qml.draw(circuit)("x")) 0: ────╭RX(x)─┤ <Z> 1: ────├○─────┤ 2: ──X─├●─────┤ 3: ────╰○─────┤ >>> x = np.array(1.2) >>> circuit(x) tensor(0.36235775, requires_grad=True) >>> qml.grad(circuit)(x) -0.9320390859672264 :func:`~.ctrl` works on both callables like ``qml.RX`` or a quantum function and individual :class:`~.operation.Operator`'s. >>> qml.ctrl(qml.PauliX(0), (1,2)) Controlled(PauliX(wires=[0]), control_wires=[1, 2]) >>> qml.ctrl(qml.PauliX(0), (1,2)).decomposition() [Toffoli(wires=[1, 2, 0])] Controlled operations work with all other forms of operator math and simplification: >>> op = qml.ctrl(qml.RX(1.2, wires=0) ** 2 @ qml.RY(0.1, wires=0), control=1) >>> qml.simplify(qml.adjoint(op)) Controlled(RY(12.466370614359173, wires=[0]) @ RX(10.166370614359172, wires=[0]), control_wires=[1]) """ control_values = [control_values] if isinstance(control_values, int) else control_values control = qml.wires.Wires(control) if isinstance(op, Operator): return Controlled( op, control_wires=control, control_values=control_values, work_wires=work_wires ) if not callable(op): raise ValueError( f"The object {op} of type {type(op)} is not an Operator or callable. " "This error might occur if you apply ctrl to a list " "of operations instead of a function or Operator." ) @wraps(op) def wrapper(*args, **kwargs): tape = qml.transforms.make_tape(op)(*args, **kwargs) # flip control_values == 0 wires here, so we don't have to do it for each individual op. flip_control_on_zero = (len(tape) > 1) and (control_values is not None) op_control_values = None if flip_control_on_zero else control_values if flip_control_on_zero: _ = [qml.PauliX(w) for w, val in zip(control, control_values) if not val] _ = [ Controlled( op, control_wires=control, control_values=op_control_values, work_wires=work_wires ) for op in tape.operations ] if flip_control_on_zero: _ = [qml.PauliX(w) for w, val in zip(control, control_values) if not val] if qml.QueuingContext.recording(): _ = [qml.apply(m) for m in tape.measurements] return tape.measurements return wrapper