Quellcode für qiskit.transpiler.passes.optimization.optimize_cliffords

# This code is part of Qiskit.
# (C) Copyright IBM 2017, 2021.
# 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.

"""Combine consecutive Cliffords over the same qubits."""

from qiskit.transpiler.basepasses import TransformationPass
from qiskit.transpiler.passes.utils import control_flow
from qiskit.quantum_info.operators import Clifford

[Doku]class OptimizeCliffords(TransformationPass): """Combine consecutive Cliffords over the same qubits. This serves as an example of extra capabilities enabled by storing Cliffords natively on the circuit. """
[Doku] @control_flow.trivial_recurse def run(self, dag): """Run the OptimizeCliffords pass on `dag`. Args: dag (DAGCircuit): the DAG to be optimized. Returns: DAGCircuit: the optimized DAG. """ blocks = [] prev_node = None cur_block = [] # Iterate over all nodes and collect consecutive Cliffords over the # same qubits. In this very first proof-of-concept implementation # we require the same ordering of qubits, but this restriction will # be shortly removed. An interesting question is whether we may also # want to compose Cliffords over different sets of qubits, such as # cliff1 over qubits [1, 2, 3] and cliff2 over [2, 3, 4]. for node in dag.topological_op_nodes(): if isinstance(node.op, Clifford): if prev_node is None: blocks.append(cur_block) cur_block = [node] else: if prev_node.qargs == node.qargs: cur_block.append(node) else: blocks.append(cur_block) cur_block = [node] prev_node = node else: # not a clifford if cur_block: blocks.append(cur_block) prev_node = None cur_block = [] if cur_block: blocks.append(cur_block) # Replace every discovered block of cliffords by a single clifford # based on the Cliffords' compose function. for cur_nodes in blocks: # Create clifford functions only out of blocks with at least 2 gates if len(cur_nodes) <= 1: continue wire_pos_map = {qb: ix for ix, qb in enumerate(cur_nodes[0].qargs)} # Construct a linear circuit cliff = cur_nodes[0].op for i, node in enumerate(cur_nodes): if i > 0: cliff = Clifford.compose(node.op, cliff, front=True) # Replace the block by the composed clifford dag.replace_block_with_op(cur_nodes, cliff, wire_pos_map, cycle_check=False) return dag