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gates.py
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gates.py
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# Copyright 2018 The Cirq Developers
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import functools
import itertools
import math
import operator
from typing import Dict, Iterable, List, NamedTuple, Optional, Sequence, Tuple, TYPE_CHECKING
from cirq import ops, protocols, value
from cirq.contrib.acquaintance.shift import CircularShiftGate
from cirq.contrib.acquaintance.permutation import (
PermutationGate,
SwapPermutationGate,
LinearPermutationGate,
)
if TYPE_CHECKING:
import cirq
def operations_to_part_lens(
qubit_order: Sequence['cirq.Qid'], op_tree: 'cirq.OP_TREE'
) -> Tuple[int, ...]:
qubit_sort_key = functools.partial(operator.indexOf, qubit_order)
op_parts = [tuple(sorted(op.qubits, key=qubit_sort_key)) for op in ops.flatten_op_tree(op_tree)]
singletons: List[Tuple['cirq.Qid', ...]] = [
(q,) for q in set(qubit_order).difference(*op_parts)
]
part_sort_key = lambda p: min(qubit_sort_key(q) for q in p)
parts = tuple(tuple(part) for part in sorted(singletons + op_parts, key=part_sort_key))
if sum(parts, ()) != tuple(qubit_order):
raise ValueError('sum(parts, ()) != tuple(qubit_order)')
return tuple(len(part) for part in parts)
class AcquaintanceOpportunityGate(ops.Gate, ops.InterchangeableQubitsGate):
"""Represents an acquaintance opportunity. An acquaintance opportunity is
essentially a placeholder in a swap network that may later be replaced with
a logical gate."""
def __init__(self, num_qubits: int):
self._num_qubits = num_qubits
def __repr__(self) -> str:
return (
'cirq.contrib.acquaintance.AcquaintanceOpportunityGate('
f'num_qubits={self.num_qubits()!r})'
)
def _circuit_diagram_info_(self, args: 'cirq.CircuitDiagramInfoArgs') -> Iterable[str]:
wire_symbol = '█' if args.use_unicode_characters else 'Acq'
wire_symbols = (wire_symbol,) * self.num_qubits()
return wire_symbols
def num_qubits(self) -> int:
return self._num_qubits
def acquaint(*qubits) -> 'cirq.Operation':
return AcquaintanceOpportunityGate(len(qubits)).on(*qubits)
Layers = NamedTuple(
'Layers',
[
('prior_interstitial', List['cirq.Operation']),
('pre', List['cirq.Operation']),
('intra', List['cirq.Operation']),
('post', List['cirq.Operation']),
('posterior_interstitial', List['cirq.Operation']),
],
)
def new_layers(**kwargs: List['cirq.Operation']) -> Layers:
return Layers._make(kwargs.get(field, []) for field in Layers._fields)
def acquaint_insides(
swap_gate: 'cirq.Gate',
acquaintance_gate: 'cirq.Operation',
qubits: Sequence['cirq.Qid'],
before: bool,
layers: Layers,
mapping: Dict[ops.Qid, int],
) -> None:
"""Acquaints each of the qubits with another set specified by an
acquaintance gate.
Args:
qubits: The list of qubits of which half are individually acquainted
with another list of qubits.
layers: The layers to put gates into.
acquaintance_gate: The acquaintance gate that acquaints the end qubit
with another list of qubits.
before: Whether the acquainting is done before the shift.
swap_gate: The gate used to swap logical indices.
mapping: The mapping from qubits to logical indices. Used to keep track
of the effect of inside-acquainting swaps.
"""
max_reach = _get_max_reach(len(qubits), round_up=before)
reaches = itertools.chain(range(1, max_reach + 1), range(max_reach, -1, -1))
offsets = (0, 1) * max_reach
swap_gate = SwapPermutationGate(swap_gate)
ops = []
for offset, reach in zip(offsets, reaches):
if offset == before:
ops.append(acquaintance_gate)
for dr in range(offset, reach, 2):
ops.append(swap_gate(*qubits[dr : dr + 2]))
intrastitial_layer = getattr(layers, 'pre' if before else 'post')
intrastitial_layer += ops
# add interstitial gate
interstitial_layer = getattr(layers, ('prior' if before else 'posterior') + '_interstitial')
interstitial_layer.append(acquaintance_gate)
# update mapping
reached_qubits = qubits[: max_reach + 1]
positions = list(mapping[q] for q in reached_qubits)
mapping.update(zip(reached_qubits, reversed(positions)))
def _get_max_reach(size: int, round_up: bool = True) -> int:
if round_up:
return int(math.ceil(size / 2)) - 1
return max((size // 2) - 1, 0)
def acquaint_and_shift(
parts: Tuple[List['cirq.Qid'], List['cirq.Qid']],
layers: Layers,
acquaintance_size: Optional[int],
swap_gate: 'cirq.Gate',
mapping: Dict[ops.Qid, int],
):
"""Acquaints and shifts a pair of lists of qubits. The first part is
acquainted with every qubit individually in the second part, and vice
versa. Operations are grouped into several layers:
* prior_interstitial: The first layer of acquaintance gates.
* prior: The combination of acquaintance gates and swaps that acquaints
the inner halves.
* intra: The shift gate.
* post: The combination of acquaintance gates and swaps that acquaints
the outer halves.
* posterior_interstitial: The last layer of acquaintance gates.
Args:
parts: The two lists of qubits to acquaint.
layers: The layers to put gates into.
acquaintance_size: The number of qubits to acquaint at a time. If None,
after each pair of parts is shifted the union thereof is
acquainted.
swap_gate: The gate used to swap logical indices.
mapping: The mapping from qubits to logical indices. Used to keep track
of the effect of inside-acquainting swaps.
"""
left_part, right_part = parts
left_size, right_size = len(left_part), len(right_part)
assert not (set(left_part) & set(right_part))
qubits = left_part + right_part
shift = CircularShiftGate(len(qubits), left_size, swap_gate=swap_gate)(*qubits)
if acquaintance_size is None:
layers.intra.append(shift)
layers.post.append(acquaint(*qubits))
shift.gate.update_mapping(mapping, qubits)
elif max(left_size, right_size) != acquaintance_size - 1:
layers.intra.append(shift)
shift.gate.update_mapping(mapping, qubits)
elif acquaintance_size == 2:
layers.prior_interstitial.append(acquaint(*qubits))
layers.intra.append(shift)
shift.gate.update_mapping(mapping, qubits)
else:
# before
if left_size == acquaintance_size - 1:
# right part
pre_acquaintance_gate = acquaint(*qubits[:acquaintance_size])
acquaint_insides(
swap_gate=swap_gate,
acquaintance_gate=pre_acquaintance_gate,
qubits=right_part,
before=True,
layers=layers,
mapping=mapping,
)
if right_size == acquaintance_size - 1:
# left part
pre_acquaintance_gate = acquaint(*qubits[-acquaintance_size:])
acquaint_insides(
swap_gate=swap_gate,
acquaintance_gate=pre_acquaintance_gate,
qubits=left_part[::-1],
before=True,
layers=layers,
mapping=mapping,
)
layers.intra.append(shift)
shift.gate.update_mapping(mapping, qubits)
# after
if (left_size == acquaintance_size - 1) and (right_size > 1):
# right part
post_acquaintance_gate = acquaint(*qubits[-acquaintance_size:])
new_left_part = qubits[right_size - 1 :: -1]
acquaint_insides(
swap_gate=swap_gate,
acquaintance_gate=post_acquaintance_gate,
qubits=new_left_part,
before=False,
layers=layers,
mapping=mapping,
)
if (right_size == acquaintance_size - 1) and (left_size > 1):
# left part
post_acquaintance_gate = acquaint(*qubits[:acquaintance_size])
acquaint_insides(
swap_gate=swap_gate,
acquaintance_gate=post_acquaintance_gate,
qubits=qubits[right_size:],
before=False,
layers=layers,
mapping=mapping,
)
@value.value_equality
class SwapNetworkGate(PermutationGate):
"""A single gate representing a generalized swap network.
Args:
part_lens: An sequence indicating the sizes of the parts in the
partition defining the swap network.
acquaintance_size: An int indicating the locality of the logical gates
desired; used to keep track of this while nesting. If 0, no
acquaintance gates are inserted. If None, after each pair of parts
is shifted the union thereof is acquainted.
swap_gate: The gate used to swap logical indices.
Attributes:
part_lens: See above.
acquaintance_size: See above.
swap_gate: The gate used to swap logical indices.
"""
def __init__(
self,
part_lens: Sequence[int],
acquaintance_size: Optional[int] = 0,
swap_gate: 'cirq.Gate' = ops.SWAP,
) -> None:
super().__init__(sum(part_lens), swap_gate)
if len(part_lens) < 2:
raise ValueError('len(part_lens) < 2.')
self.part_lens = tuple(part_lens)
self.acquaintance_size = acquaintance_size
def _decompose_(self, qubits: Sequence['cirq.Qid']) -> 'cirq.OP_TREE':
qubit_to_position = {q: i for i, q in enumerate(qubits)}
mapping = dict(qubit_to_position)
parts = []
n_qubits = 0
for part_len in self.part_lens:
parts.append(list(qubits[n_qubits : n_qubits + part_len]))
n_qubits += part_len
n_parts = len(parts)
op_sort_key = (
None
if self.acquaintance_size is None
else (lambda op: min(qubit_to_position[q] for q in op.qubits) % self.acquaintance_size)
)
layers = new_layers()
for layer_num in range(n_parts):
layers = new_layers(prior_interstitial=layers.posterior_interstitial)
for i in range(layer_num % 2, n_parts - 1, 2):
left_part, right_part = parts[i : i + 2]
acquaint_and_shift(
parts=(left_part, right_part),
layers=layers,
acquaintance_size=self.acquaintance_size,
swap_gate=self.swap_gate,
mapping=mapping,
)
parts_qubits = list(left_part + right_part)
parts[i] = parts_qubits[: len(right_part)]
parts[i + 1] = parts_qubits[len(right_part) :]
layers.prior_interstitial.sort(key=op_sort_key)
for l in ('prior_interstitial', 'pre', 'intra', 'post'):
yield getattr(layers, l)
layers.posterior_interstitial.sort(key=op_sort_key)
yield layers.posterior_interstitial
assert list(
itertools.chain(*(sorted(mapping[q] for q in part) for part in reversed(parts)))
) == list(range(n_qubits))
# finish reversal
final_permutation = {i: n_qubits - 1 - mapping[q] for i, q in enumerate(qubits)}
final_gate = LinearPermutationGate(n_qubits, final_permutation, self.swap_gate)
if final_gate:
yield final_gate(*qubits)
def _circuit_diagram_info_(
self, args: 'cirq.CircuitDiagramInfoArgs'
) -> 'cirq.CircuitDiagramInfo':
wire_symbol = '×' if args.use_unicode_characters else 'swap'
wire_symbols = tuple(
wire_symbol + f'({part_index},{qubit_index})'
for part_index, part_len in enumerate(self.part_lens)
for qubit_index in range(part_len)
)
return protocols.CircuitDiagramInfo(wire_symbols=wire_symbols)
@staticmethod
def from_operations(
qubit_order: Sequence['cirq.Qid'],
operations: Sequence['cirq.Operation'],
acquaintance_size: Optional[int] = 0,
swap_gate: 'cirq.Gate' = ops.SWAP,
) -> 'SwapNetworkGate':
part_sizes = operations_to_part_lens(qubit_order, operations)
return SwapNetworkGate(part_sizes, acquaintance_size, swap_gate)
def permutation(self) -> Dict[int, int]:
return {i: j for i, j in enumerate(reversed(range(sum(self.part_lens))))}
def __repr__(self) -> str:
return 'cirq.contrib.acquaintance.SwapNetworkGate({!r}, {!r})'.format(
self.part_lens, self.acquaintance_size
)
def _value_equality_values_(self):
return (self.part_lens, self.acquaintance_size, self.swap_gate)