C贸digo fuente para qiskit.transpiler.passes.optimization.cx_cancellation

# This code is part of Qiskit.
# (C) Copyright IBM 2017, 2018.
# 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.

"""Cancel back-to-back `cx` gates in dag."""

from qiskit.transpiler.basepasses import TransformationPass
from qiskit.transpiler.passes.utils import control_flow

[documentos]class CXCancellation(TransformationPass): """Cancel back-to-back `cx` gates in dag."""
[documentos] @control_flow.trivial_recurse def run(self, dag): """Run the CXCancellation pass on `dag`. Args: dag (DAGCircuit): the directed acyclic graph to run on. Returns: DAGCircuit: Transformed DAG. """ cx_runs = dag.collect_runs(["cx"]) for cx_run in cx_runs: # Although one `cx_run` will always have the same set of qubits, # the order of these qubits matters (CXi_j != CXj_i). # Therefore, we have to partition each run into chunks where the qargs # are in the same order, and only cancel out CXs within each chunk. partitions = [] chunk = [] for i in range(len(cx_run) - 1): chunk.append(cx_run[i]) if cx_run[i].qargs != cx_run[i + 1].qargs: partitions.append(chunk) chunk = [] chunk.append(cx_run[-1]) partitions.append(chunk) # Remove an even number of CX gates from each chunk for chunk in partitions: if len(chunk) % 2 == 0: dag.remove_op_node(chunk[0]) for node in chunk[1:]: dag.remove_op_node(node) return dag