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Source code for mrmustard.lab.transformations.s2gate

# 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 class representing a two-mode squeezing gate."""

from __future__ import annotations

from collections.abc import Sequence

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

from .base import Unitary
from .builtins import twomode_squeezing_gate

__all__ = ["S2gate"]




[docs]
class S2gate(Unitary):
    r"""The two-mode squeezing gate.

    >>> from mrmustard.lab import S2gate
    >>> unitary = S2gate(modes=(1, 2), r=1)
    >>> assert unitary.modes == (1, 2)
    >>> assert unitary.parameters.r.value == 1
    >>> assert unitary.parameters.phi.value == 0.0

    Args:
        modes: The pair of modes of the two-mode squeezing gate.
        r: The squeezing amplitude.
        phi: The phase angle.
        name: A name for the gate. If not provided, the class name will be used.

    .. details::

        Its ``(A,b,c)`` triple is given by

        .. math::
            A = \begin{bmatrix}
                    O & e^{i\phi}\tanh(r) & \sech(r) & 0 \\
                    e^{i\phi}\tanh(r) & 0 & 0 & \sech(r) \\
                    \sech(r) & & 0 & 0 -e^{i\phi}\tanh(r) \\
                    O & \sech(r) & -e^{i\phi}\tanh(r) & 0
                \end{bmatrix} \text{, }
            b = O_{4} \text{, and }
            c = \sech(r)
    """

    short_name = "S2"

    def __init__(
        self,
        modes: tuple[int, int],
        r: float | Sequence[float] | Parameter = 0.0,
        phi: float | Sequence[float] | Parameter = 0.0,
        name: str | None = None,
    ):
        name = name if name is not None else self.__class__.__name__
        super().__init__(
            ansatz_factory=AnsatzFactory(
                ansatz_dict={ReprEnum.BARGMANN: (twomode_squeezing_gate, ("r", "phi", "lin_sup"))}
            ),
            wires=Wires(modes_in_ket=set(modes), modes_out_ket=set(modes)),
            name=name,
        )
        self.parameters["r"] = Parameter.from_cc_init(r, "float64", f"{self.name}/r")
        self.parameters["phi"] = Parameter.from_cc_init(phi, "float64", f"{self.name}/phi")