Source code for qiskit.extensions.quantum_initializer.ucrz

# This code is part of Qiskit.
#
# (C) Copyright IBM 2020.
#
# This code is licensed under the Apache License, Version 2.0. You may
# obtain a copy of this license in the LICENSE.txt file in the root directory
# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
#
# Any modifications or derivative works of this code must retain this
# copyright notice, and modified files need to carry a notice indicating
# that they have been altered from the originals.

"""
Implementation of the abstract class UCPauliRotGate for uniformly controlled
(also called multiplexed) single-qubit rotations
around the Z-axes (i.e., uniformly controlled R_z rotations).
These gates can have several control qubits and a single target qubit.
If the k control qubits are in the state ket(i) (in the computational bases),
a single-qubit rotation R_z(a_i) is applied to the target qubit.
"""
import math

from qiskit.circuit.quantumcircuit import QuantumCircuit
from qiskit.circuit.quantumregister import QuantumRegister
from qiskit.exceptions import QiskitError
from qiskit.extensions.quantum_initializer.uc_pauli_rot import UCPauliRotGate


class UCRZGate(UCPauliRotGate):
    """
    Uniformly controlled rotations (also called multiplexed rotations).
    The decomposition is based on
    'Synthesis of Quantum Logic Circuits' by V. Shende et al.
    (https://arxiv.org/pdf/quant-ph/0406176.pdf)

    Input:
    angle_list = list of (real) rotation angles [a_0,...,a_{2^k-1}]
    """

    def __init__(self, angle_list):
        super().__init__(angle_list, "Z")


def ucrz(self, angle_list, q_controls, q_target):
    """Attach a uniformly controlled (also called multiplexed gates) Rz rotation gate to a circuit.

    The decomposition is base on https://arxiv.org/pdf/quant-ph/0406176.pdf by Shende et al.

    Args:
        angle_list (list[numbers): list of (real) rotation angles [a_0,...,a_{2^k-1}]
        q_controls (QuantumRegister|list[Qubit]): list of k control qubits
            (or empty list if no controls). The control qubits are ordered according to their
            significance in increasing order: For example if q_controls=[q[1],q[2]]
            (with q = QuantumRegister(2)), the rotation Rz(a_0)is performed if q[1] and q[2]
            are in the state zero, the rotation  Rz(a_1) is performed if q[1] is in
            the state one and q[2] is in the state zero, and so on
        q_target (QuantumRegister|Qubit): target qubit, where we act on with
            the single-qubit rotation gates

    Returns:
        QuantumCircuit: the uniformly controlled rotation gate is attached to the circuit.

    Raises:
        QiskitError: if the list number of control qubits does not correspond to
            the provided number of single-qubit unitaries; if an input is of
            the wrong type
    """

    if isinstance(q_controls, QuantumRegister):
        q_controls = q_controls[:]
    if isinstance(q_target, QuantumRegister):
        q_target = q_target[:]
        if len(q_target) == 1:
            q_target = q_target[0]
        else:
            raise QiskitError(
                "The target qubit is a QuantumRegister containing" " more than one qubits."
            )
    # Check if q_controls has type "list"
    if not isinstance(angle_list, list):
        raise QiskitError("The angles must be provided as a list.")
    num_contr = math.log2(len(angle_list))
    if num_contr < 0 or not num_contr.is_integer():
        raise QiskitError(
            "The number of controlled rotation gates is not a non-negative" " power of 2."
        )
    # Check if number of control qubits does correspond to the number of rotations
    if num_contr != len(q_controls):
        raise QiskitError(
            "Number of controlled rotations does not correspond to the number" " of control-qubits."
        )
    return self.append(UCRZGate(angle_list), [q_target] + q_controls, [])


QuantumCircuit.ucrz = ucrz