C贸digo fuente para qiskit.transpiler.passes.utils.barrier_before_final_measurements

# 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.

"""Add a barrier before final measurements."""

from qiskit.circuit.barrier import Barrier
from qiskit.transpiler.basepasses import TransformationPass
from qiskit.dagcircuit import DAGCircuit, DAGOpNode
from .merge_adjacent_barriers import MergeAdjacentBarriers

[documentos]class BarrierBeforeFinalMeasurements(TransformationPass): """Add a barrier before final measurements. This pass adds a barrier before the set of final measurements. Measurements are considered final if they are followed by no other operations (aside from other measurements or barriers.) """
[documentos] def run(self, dag): """Run the BarrierBeforeFinalMeasurements pass on `dag`.""" # Collect DAG nodes which are followed only by barriers or other measures. final_op_types = ["measure", "barrier"] final_ops = [] for candidate_node in dag.named_nodes(*final_op_types): is_final_op = True for _, child_successors in dag.bfs_successors(candidate_node): if any( isinstance(suc, DAGOpNode) and suc.name not in final_op_types for suc in child_successors ): is_final_op = False break if is_final_op: final_ops.append(candidate_node) if not final_ops: return dag # Create a layer with the barrier and add both bits and registers from the original dag. barrier_layer = DAGCircuit() barrier_layer.add_qubits(dag.qubits) for qreg in dag.qregs.values(): barrier_layer.add_qreg(qreg) barrier_layer.add_clbits(dag.clbits) for creg in dag.cregs.values(): barrier_layer.add_creg(creg) # Add a barrier across all qubits so swap mapper doesn't add a swap # from an unmeasured qubit after a measure. final_qubits = dag.qubits barrier_layer.apply_operation_back(Barrier(len(final_qubits)), list(final_qubits), []) # Preserve order of final ops collected earlier from the original DAG. ordered_final_nodes = [ node for node in dag.topological_op_nodes() if node in set(final_ops) ] # Move final ops to the new layer and append the new layer to the DAG. for final_node in ordered_final_nodes: barrier_layer.apply_operation_back(final_node.op, final_node.qargs, final_node.cargs) for final_op in final_ops: dag.remove_op_node(final_op) dag.compose(barrier_layer) # Merge the new barrier into any other barriers adjacent_pass = MergeAdjacentBarriers() return adjacent_pass.run(dag)