# qiskit.circuit.library.n_local.excitation_preserving의 소스 코드

# This code is part of Qiskit.
#
# (C) Copyright IBM 2017, 2020.
#
# obtain a copy of this license in the LICENSE.txt file in the root directory
#
# 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.

"""The ExcitationPreserving 2-local circuit."""

from __future__ import annotations
from collections.abc import Callable
from numpy import pi

from qiskit.circuit import QuantumCircuit, Parameter
from qiskit.circuit.library.standard_gates import RZGate
from .two_local import TwoLocal

[문서]class ExcitationPreserving(TwoLocal):
r"""The heuristic excitation-preserving wave function ansatz.

The ExcitationPreserving circuit preserves the ratio of :math:|00\rangle,
:math:|01\rangle + |10\rangle and :math:|11\rangle states. To this end, this circuit
uses two-qubit interactions of the form

.. math::

\newcommand{\th}{\theta/2}

\begin{pmatrix}
1 & 0 & 0 & 0 \\
0 & \cos\left(\th\right) & -i\sin\left(\th\right) & 0 \\
0 & -i\sin\left(\th\right) & \cos\left(\th\right) & 0 \\
0 & 0 & 0 & e^{-i\phi}
\end{pmatrix}

for the mode 'fsim' or with :math:e^{-i\phi} = 1 for the mode 'iswap'.

Note that other wave functions, such as UCC-ansatzes, are also excitation preserving.
However these can become complex quickly, while this heuristically motivated circuit follows
a simpler pattern.

This trial wave function consists of layers of :math:Z rotations with 2-qubit entanglements.
The entangling is creating using :math:XX+YY rotations and optionally a controlled-phase
gate for the mode 'fsim'.

See :class:~qiskit.circuit.library.RealAmplitudes for more detail on the possible arguments
and options such as skipping unentanglement qubits, which apply here too.

The rotations of the ExcitationPreserving ansatz can be written as

Examples:

>>> ansatz = ExcitationPreserving(3, reps=1, insert_barriers=True, entanglement='linear')
>>> print(ansatz)  # show the circuit
┌──────────┐ ░ ┌────────────┐┌────────────┐                             ░ ┌──────────┐
q_0: ┤ RZ(θ[0]) ├─░─┤0           ├┤0           ├─────────────────────────────░─┤ RZ(θ[5]) ├
├──────────┤ ░ │  RXX(θ[3]) ││  RYY(θ[3]) │┌────────────┐┌────────────┐ ░ ├──────────┤
q_1: ┤ RZ(θ[1]) ├─░─┤1           ├┤1           ├┤0           ├┤0           ├─░─┤ RZ(θ[6]) ├
├──────────┤ ░ └────────────┘└────────────┘│  RXX(θ[4]) ││  RYY(θ[4]) │ ░ ├──────────┤
q_2: ┤ RZ(θ[2]) ├─░─────────────────────────────┤1           ├┤1           ├─░─┤ RZ(θ[7]) ├
└──────────┘ ░                             └────────────┘└────────────┘ ░ └──────────┘

>>> ansatz = ExcitationPreserving(2, reps=1)
>>> qc = QuantumCircuit(2)  # create a circuit and append the RY variational form
>>> qc.cry(0.2, 0, 1)  # do some previous operation
>>> qc.compose(ansatz, inplace=True)  # add the swaprz
>>> qc.draw()
┌──────────┐┌────────────┐┌────────────┐┌──────────┐
q_0: ─────■─────┤ RZ(θ[0]) ├┤0           ├┤0           ├┤ RZ(θ[3]) ├
┌────┴────┐├──────────┤│  RXX(θ[2]) ││  RYY(θ[2]) │├──────────┤
q_1: ┤ RY(0.2) ├┤ RZ(θ[1]) ├┤1           ├┤1           ├┤ RZ(θ[4]) ├
└─────────┘└──────────┘└────────────┘└────────────┘└──────────┘

>>> ansatz = ExcitationPreserving(3, reps=1, mode='fsim', entanglement=[[0,2]],
... insert_barriers=True)
>>> print(ansatz)
┌──────────┐ ░ ┌────────────┐┌────────────┐        ░ ┌──────────┐
q_0: ┤ RZ(θ[0]) ├─░─┤0           ├┤0           ├─■──────░─┤ RZ(θ[5]) ├
├──────────┤ ░ │            ││            │ │      ░ ├──────────┤
q_1: ┤ RZ(θ[1]) ├─░─┤  RXX(θ[3]) ├┤  RYY(θ[3]) ├─┼──────░─┤ RZ(θ[6]) ├
├──────────┤ ░ │            ││            │ │θ[4]  ░ ├──────────┤
q_2: ┤ RZ(θ[2]) ├─░─┤1           ├┤1           ├─■──────░─┤ RZ(θ[7]) ├
└──────────┘ ░ └────────────┘└────────────┘        ░ └──────────┘
"""

def __init__(
self,
num_qubits: int | None = None,
mode: str = "iswap",
entanglement: str | list[list[int]] | Callable[[int], list[int]] = "full",
reps: int = 3,
skip_unentangled_qubits: bool = False,
skip_final_rotation_layer: bool = False,
parameter_prefix: str = "θ",
insert_barriers: bool = False,
initial_state: QuantumCircuit | None = None,
name: str = "ExcitationPreserving",
flatten: bool | None = None,
) -> None:
"""
Args:
num_qubits: The number of qubits of the ExcitationPreserving circuit.
mode: Choose the entangler mode, can be 'iswap' or 'fsim'.
reps: Specifies how often the structure of a rotation layer followed by an entanglement
layer is repeated.
entanglement: Specifies the entanglement structure. Can be a string ('full', 'linear'
or 'sca'), a list of integer-pairs specifying the indices of qubits
entangled with one another, or a callable returning such a list provided with
the index of the entanglement layer.
See the Examples section of :class:~qiskit.circuit.library.TwoLocal for more
detail.
initial_state: A QuantumCircuit object to prepend to the circuit.
skip_unentangled_qubits: If True, the single qubit gates are only applied to qubits
that are entangled with another qubit. If False, the single qubit gates are applied
to each qubit in the Ansatz. Defaults to False.
skip_unentangled_qubits: If True, the single qubit gates are only applied to qubits
that are entangled with another qubit. If False, the single qubit gates are applied
to each qubit in the Ansatz. Defaults to False.
skip_final_rotation_layer: If True, a rotation layer is added at the end of the
ansatz. If False, no rotation layer is added. Defaults to True.
parameter_prefix: The parameterized gates require a parameter to be defined, for which
we use :class:~qiskit.circuit.ParameterVector.
insert_barriers: If True, barriers are inserted in between each layer. If False,
no barriers are inserted.
flatten: Set this to True to output a flat circuit instead of nesting it inside multiple
layers of gate objects. By default currently the contents of
the output circuit will be wrapped in nested objects for
cleaner visualization. However, if you're using this circuit
for anything besides visualization its **strongly** recommended
to set this flag to True to avoid a large performance

Raises:
ValueError: If the selected mode is not supported.
"""
supported_modes = ["iswap", "fsim"]
if mode not in supported_modes:
raise ValueError(f"Unsupported mode {mode}, choose one of {supported_modes}")

theta = Parameter("θ")
swap = QuantumCircuit(2, name="Interaction")
swap.rxx(theta, 0, 1)
swap.ryy(theta, 0, 1)
if mode == "fsim":
phi = Parameter("φ")
swap.cp(phi, 0, 1)

super().__init__(
num_qubits=num_qubits,
rotation_blocks=RZGate,
entanglement_blocks=swap,
entanglement=entanglement,
reps=reps,
skip_unentangled_qubits=skip_unentangled_qubits,
skip_final_rotation_layer=skip_final_rotation_layer,
parameter_prefix=parameter_prefix,
insert_barriers=insert_barriers,
initial_state=initial_state,
name=name,
flatten=flatten,
)

@property
def parameter_bounds(self) -> list[tuple[float, float]]:
"""Return the parameter bounds.

Returns:
The parameter bounds.
"""
return self.num_parameters * [(-pi, pi)]