# 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.
"""Double-CNOT gate."""
from qiskit.circuit.gate import Gate
from qiskit.circuit.quantumregister import QuantumRegister
from qiskit.circuit._utils import with_gate_array
[docs]@with_gate_array([[1, 0, 0, 0], [0, 0, 0, 1], [0, 1, 0, 0], [0, 0, 1, 0]])
class DCXGate(Gate):
r"""Double-CNOT gate.
A 2-qubit Clifford gate consisting of two back-to-back
CNOTs with alternate controls.
Can be applied to a :class:`~qiskit.circuit.QuantumCircuit`
with the :meth:`~qiskit.circuit.QuantumCircuit.dcx` method.
.. parsed-literal::
┌───┐
q_0: ──■──┤ X ├
┌─┴─┐└─┬─┘
q_1: ┤ X ├──■──
└───┘
This is a classical logic gate, equivalent to a CNOT-SWAP (CNS) sequence,
and locally equivalent to an iSWAP.
.. math::
DCX\ q_0, q_1 =
\begin{pmatrix}
1 & 0 & 0 & 0 \\
0 & 0 & 0 & 1 \\
0 & 1 & 0 & 0 \\
0 & 0 & 1 & 0
\end{pmatrix}
"""
def __init__(self):
"""Create new DCX gate."""
super().__init__("dcx", 2, [])
def _define(self):
"""
gate dcx a, b { cx a, b; cx b, a; }
"""
# pylint: disable=cyclic-import
from qiskit.circuit.quantumcircuit import QuantumCircuit
from .x import CXGate
q = QuantumRegister(2, "q")
qc = QuantumCircuit(q, name=self.name)
rules = [(CXGate(), [q[0], q[1]], []), (CXGate(), [q[1], q[0]], [])]
for instr, qargs, cargs in rules:
qc._append(instr, qargs, cargs)
self.definition = qc