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Source code for mrmustard.lab.transformations.identity

# Copyright 2023 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.

"""The classes representing an identity gate."""

from __future__ import annotations

from mrmustard.physics.ansatz_factory import AnsatzFactory
from mrmustard.physics.wires import ReprEnum, Wires

from .base import Unitary
from .builtins import identity_gate

__all__ = ["Identity"]




[docs]
class Identity(Unitary):
    r"""The identity gate.

    >>> from mrmustard.lab import Identity
    >>> unitary = Identity(modes=(1, 2))
    >>> assert unitary.modes == (1, 2)

    Args:
        modes: The modes this gate is applied to.
        name: A name for the gate. If not provided, the class name will be used.

    .. details::

        The Abc parametrization of the identity gate is given by (c.f. https://www.scipost.org/10.21468/SciPostPhys.17.3.082)
        .. math::

            A = \begin{pmatrix}
                0 & 1 \\
                1 & 0
            \end{pmatrix},
            \quad

            b = \begin{pmatrix}
                0 \\
                0
            \end{pmatrix},
            \quad
            c = 1
    """

    short_name = "I"

    def __init__(
        self,
        modes: int | tuple[int, ...],
        name: str | None = None,
    ):
        modes = (modes,) if isinstance(modes, int) else modes
        name = name if name is not None else self.__class__.__name__
        super().__init__(
            ansatz_factory=AnsatzFactory(
                ansatz_dict={ReprEnum.BARGMANN: (identity_gate, ("n_modes", "lin_sup"))},
                n_modes=len(modes),
            ),
            wires=Wires(
                modes_in_bra=set(),
                modes_out_bra=set(),
                modes_in_ket=set(modes),
                modes_out_ket=set(modes),
            ),
            name=name,
        )