/
ryy.py
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/
ryy.py
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# This code is part of Qiskit.
#
# (C) Copyright IBM 2017, 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.
"""Two-qubit YY-rotation gate."""
import math
from typing import Optional
import numpy as np
from qiskit.circuit.gate import Gate
from qiskit.circuit.quantumregister import QuantumRegister
from qiskit.circuit.parameterexpression import ParameterValueType
class RYYGate(Gate):
r"""A parametric 2-qubit :math:`Y \otimes Y` interaction (rotation about YY).
This gate is symmetric, and is maximally entangling at :math:`\theta = \pi/2`.
Can be applied to a :class:`~qiskit.circuit.QuantumCircuit`
with the :meth:`~qiskit.circuit.QuantumCircuit.ryy` method.
**Circuit Symbol:**
.. parsed-literal::
┌─────────┐
q_0: ┤1 ├
│ Ryy(ϴ) │
q_1: ┤0 ├
└─────────┘
**Matrix Representation:**
.. math::
\newcommand{\rotationangle}{\frac{\theta}{2}}
R_{YY}(\theta) = \exp\left(-i \rotationangle Y{\otimes}Y\right) =
\begin{pmatrix}
\cos\left(\rotationangle\right) & 0 & 0 & i\sin\left(\rotationangle\right) \\
0 & \cos\left(\rotationangle\right) & -i\sin\left(\rotationangle\right) & 0 \\
0 & -i\sin\left(\rotationangle\right) & \cos\left(\rotationangle\right) & 0 \\
i\sin\left(\rotationangle\right) & 0 & 0 & \cos\left(\rotationangle\right)
\end{pmatrix}
**Examples:**
.. math::
R_{YY}(\theta = 0) = I
.. math::
R_{YY}(\theta = \pi) = i Y \otimes Y
.. math::
R_{YY}\left(\theta = \frac{\pi}{2}\right) = \frac{1}{\sqrt{2}}
\begin{pmatrix}
1 & 0 & 0 & i \\
0 & 1 & -i & 0 \\
0 & -i & 1 & 0 \\
i & 0 & 0 & 1
\end{pmatrix}
"""
def __init__(
self, theta: ParameterValueType, label: Optional[str] = None, *, duration=None, unit="dt"
):
"""Create new RYY gate."""
super().__init__("ryy", 2, [theta], label=label, duration=duration, unit=unit)
def _define(self):
"""Calculate a subcircuit that implements this unitary."""
# pylint: disable=cyclic-import
from qiskit.circuit.quantumcircuit import QuantumCircuit
from .x import CXGate
from .rx import RXGate
from .rz import RZGate
# ┌─────────┐ ┌──────────┐
# q_0: ┤ Rx(π/2) ├──■─────────────■──┤ Rx(-π/2) ├
# ├─────────┤┌─┴─┐┌───────┐┌─┴─┐├──────────┤
# q_1: ┤ Rx(π/2) ├┤ X ├┤ Rz(0) ├┤ X ├┤ Rx(-π/2) ├
# └─────────┘└───┘└───────┘└───┘└──────────┘
q = QuantumRegister(2, "q")
theta = self.params[0]
qc = QuantumCircuit(q, name=self.name)
rules = [
(RXGate(np.pi / 2), [q[0]], []),
(RXGate(np.pi / 2), [q[1]], []),
(CXGate(), [q[0], q[1]], []),
(RZGate(theta), [q[1]], []),
(CXGate(), [q[0], q[1]], []),
(RXGate(-np.pi / 2), [q[0]], []),
(RXGate(-np.pi / 2), [q[1]], []),
]
for instr, qargs, cargs in rules:
qc._append(instr, qargs, cargs)
self.definition = qc
def inverse(self, annotated: bool = False):
"""Return inverse RYY gate (i.e. with the negative rotation angle).
Args:
annotated: when set to ``True``, this is typically used to return an
:class:`.AnnotatedOperation` with an inverse modifier set instead of a concrete
:class:`.Gate`. However, for this class this argument is ignored as the inverse
of this gate is always a :class:`.RYYGate` with an inverted parameter value.
Returns:
RYYGate: inverse gate.
"""
return RYYGate(-self.params[0])
def __array__(self, dtype=None):
"""Return a numpy.array for the RYY gate."""
theta = float(self.params[0])
cos = math.cos(theta / 2)
isin = 1j * math.sin(theta / 2)
return np.array(
[[cos, 0, 0, isin], [0, cos, -isin, 0], [0, -isin, cos, 0], [isin, 0, 0, cos]],
dtype=dtype,
)
def power(self, exponent: float, annotated: bool = False):
(theta,) = self.params
return RYYGate(exponent * theta)
def __eq__(self, other):
if isinstance(other, RYYGate):
return self._compare_parameters(other)
return False