Source code for pennylane.templates.subroutines.flip_sign

# Copyright 2018-2021 Xanadu Quantum Technologies Inc.

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r"""
Contains the FlipSign template.
"""

import pennylane as qml
from pennylane.operation import Operation, AnyWires


[docs]class FlipSign(Operation): r"""Flips the sign of a given basis state. This template performs the following operation: FlipSign(n) :math:`|m\rangle = -|m\rangle` if :math:`m = n` FlipSign(n) :math:`|m\rangle = |m\rangle` if :math:`m \not = n`, where n is the basis state to flip and m is the input. Args: n (array[int] or int): binary array or integer value representing the state on which to flip the sign wires (array[int]): wires that the template acts on **Example** This template changes the sign of the basis state passed as an argument. In this example, when passing the element ``[1, 0]``, we will change the sign of the state :math:`|10\rangle`. We could alternatively pass the integer ``2`` and get the same result since its binary representation is ``[1, 0]``. .. code-block:: python basis_state = [1, 0] dev = qml.device("default.qubit", wires=2) @qml.qnode(dev) def circuit(): for wire in list(range(2)): qml.Hadamard(wires=wire) qml.FlipSign(basis_state, wires=list(range(2))) return qml.state() The result for the above circuit is: .. code-block:: python >>> circuit() tensor([ 0.5+0.j, 0.5+0.j, -0.5+0.j, 0.5+0.j], requires_grad=True) """ num_wires = AnyWires def __init__(self, n, wires, do_queue=True, id=None): if not isinstance(wires, int) and len(wires) == 0: raise ValueError("expected at least one wire representing the qubit ") if isinstance(wires, int): wires = 1 if wires == 0 else wires wires = list(range(wires)) if isinstance(n, int): if n >= 0: n = self.to_list(n, len(wires)) else: raise ValueError( "expected an integer equal or greater than zero for basic flipping state" ) if len(wires) != len(n): raise ValueError( "Wires length and flipping state length does not match, they must be equal length " ) self._hyperparameters = {"arr_bin": n} super().__init__(wires=wires, do_queue=do_queue, id=id)
[docs] @staticmethod def to_list(n, n_wires): r"""Convert an integer into a binary integer list Args: n (int): Basis state as integer n_wires (int): Numer of wires to transform the basis state Raises: ValueError: "cannot encode n with n wires " Returns: (array[int]): integer binary array """ if n >= 2**n_wires: raise ValueError(f"cannot encode {n} with {n_wires} wires ") b_str = f"{n:b}".zfill(n_wires) bin_list = [int(i) for i in b_str] return bin_list
@property def num_params(self): return 0
[docs] @staticmethod def compute_decomposition(wires, arr_bin): # pylint: disable=arguments-differ r"""Representation of the operator .. seealso:: :meth:`~.FlipSign.decomposition`. Args: wires (array[int]): wires that the operator acts on arr_bin (array[int]): binary array vector representing the state to flip the sign Raises: ValueError: "Wires length and flipping state length does not match, they must be equal length " Returns: list[Operator]: decomposition of the operator """ op_list = [] if arr_bin[-1] == 0: op_list.append(qml.PauliX(wires[-1])) op_list.append( qml.ctrl(qml.PauliZ, control=wires[:-1], control_values=arr_bin[:-1])(wires=wires[-1]) ) if arr_bin[-1] == 0: op_list.append(qml.PauliX(wires[-1])) return op_list