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collect_cliffords.py
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collect_cliffords.py
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# This code is part of Qiskit.
#
# (C) Copyright IBM 2022.
#
# 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.
"""Replace each sequence of Clifford gates by a single Clifford gate."""
from functools import partial
from qiskit.transpiler.passes.optimization.collect_and_collapse import (
CollectAndCollapse,
collect_using_filter_function,
collapse_to_operation,
)
from qiskit.quantum_info.operators import Clifford
class CollectCliffords(CollectAndCollapse):
"""Collects blocks of Clifford gates and replaces them by a :class:`~qiskit.quantum_info.Clifford`
object.
"""
def __init__(
self,
do_commutative_analysis=False,
split_blocks=True,
min_block_size=2,
split_layers=False,
collect_from_back=False,
):
"""CollectCliffords initializer.
Args:
do_commutative_analysis (bool): if True, exploits commutativity relations
between nodes.
split_blocks (bool): if True, splits collected blocks into sub-blocks
over disjoint qubit subsets.
min_block_size (int): specifies the minimum number of gates in the block
for the block to be collected.
split_layers (bool): if True, splits collected blocks into sub-blocks
over disjoint qubit subsets.
collect_from_back (bool): specifies if blocks should be collected started
from the end of the circuit.
"""
collect_function = partial(
collect_using_filter_function,
filter_function=_is_clifford_gate,
split_blocks=split_blocks,
min_block_size=min_block_size,
split_layers=split_layers,
collect_from_back=collect_from_back,
)
collapse_function = partial(collapse_to_operation, collapse_function=_collapse_to_clifford)
super().__init__(
collect_function=collect_function,
collapse_function=collapse_function,
do_commutative_analysis=do_commutative_analysis,
)
clifford_gate_names = [
"x",
"y",
"z",
"h",
"s",
"sdg",
"cx",
"cy",
"cz",
"swap",
"clifford",
"linear_function",
"pauli",
]
def _is_clifford_gate(node):
"""Specifies whether a node holds a clifford gate."""
return node.op.name in clifford_gate_names and getattr(node.op, "condition", None) is None
def _collapse_to_clifford(circuit):
"""Specifies how to construct a ``Clifford`` from a quantum circuit (that must
consist of Clifford gates only)."""
return Clifford(circuit)