qiskit/circuit/barrier.py

# -*- coding: utf-8 -*-

# This code is part of Qiskit.
#
# (C) Copyright IBM 2017.
#
# 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.

"""Barrier instruction."""

from qiskit.exceptions import QiskitError
from .instruction import Instruction


class Barrier(Instruction):
    """Barrier instruction."""

    def __init__(self, num_qubits):
        """Create new barrier instruction."""
        super().__init__("barrier", num_qubits, 0, [])

    def inverse(self):
        """Special case. Return self."""
        return Barrier(self.num_qubits)

    def broadcast_arguments(self, qargs, cargs):
        yield [qarg for sublist in qargs for qarg in sublist], []

    def c_if(self, classical, val):
        raise QiskitError('Barriers are compiler directives and cannot be conditional.')