Implement dynamical decoupling.

cirq-core/cirq/__init__.py

@@ -336,6 +336,7 @@
 
 from cirq.transformers import (
     AbstractInitialMapper,
+    add_dynamical_decoupling,
     align_left,
     align_right,
     CompilationTargetGateset,

cirq-core/cirq/transformers/__init__.py

@@ -78,6 +78,8 @@
 
 from cirq.transformers.drop_negligible_operations import drop_negligible_operations
 
+from cirq.transformers.dynamical_decoupling import add_dynamical_decoupling
+
 from cirq.transformers.eject_z import eject_z
 
 from cirq.transformers.measurement_transformers import (

cirq-core/cirq/transformers/dynamical_decoupling.py

@@ -0,0 +1,122 @@
+# Copyright 2024 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.
+
+"""Transformer pass that adds dynamical decoupling operations to a circuit."""
+
+from functools import reduce
+from typing import Dict, Optional, Sequence, Tuple, Union
+
+from cirq.transformers import transformer_api
+import cirq
+import numpy as np
+
+
+def _repeat_sequence(
+    base_sequence: Sequence['cirq.Gate'], num_idle_moments: int
+) -> Sequence['cirq.Gate']:
+    """Returns the longest possible dynamical decoupling sequence."""
+    repeat_times = num_idle_moments // len(base_sequence)
+    return list(base_sequence) * repeat_times
+
+
+def _get_dd_sequence_from_schema_name(schema: str) -> Sequence['cirq.Gate']:
+    """Gets dynamical decoupling sequence from a schema name."""
+    dd_sequence: Sequence['cirq.Gate']
+    match schema:
+        case 'XX_PAIR':
+            dd_sequence = (cirq.X, cirq.X)
+        case 'X_XINV':
+            dd_sequence = (cirq.X, cirq.X**-1)
+        case 'YY_PAIR':
+            dd_sequence = (cirq.Y, cirq.Y)
+        case 'Y_YINV':
+            dd_sequence = (cirq.Y, cirq.Y**-1)
+        case _:
+            raise ValueError('Invalid schema name.')
+    return dd_sequence
+
+
+def _validate_dd_sequence(dd_sequence: Sequence['cirq.Gate']) -> None:
+    """Validates a given dynamical decoupling sequence.
+
+    Args:
+        dd_sequence: Input dynamical sequence to be validated.
+
+    Returns:
+        A tuple containing:
+            - is_valid (bool): True if the dd sequence is valid, False otherwise.
+            - error_message (str): An error message if the dd sequence is invalid, else None.
+
+    Raises:
+        ValueError: If dd_sequence is not valid.
+    """
+    if len(dd_sequence) < 2:
+        raise ValueError('Invalid dynamical decoupling sequence. Expect more than one gates.')
+    matrices = [cirq.unitary(gate) for gate in dd_sequence]
+    product = reduce(np.matmul, matrices)
+
+    if not cirq.equal_up_to_global_phase(product, np.eye(2)):
+        raise ValueError(
+            'Invalid dynamical decoupling sequence. Expect sequence production equals'
+            f' identity up to a global phase, got {product}.'.replace('\n', ' ')
+        )
+
+
+def _parse_dd_sequence(schema: Union[str, Sequence['cirq.Gate']]) -> Sequence['cirq.Gate']:
+    """Parses and returns dynamical decoupling sequence from schema."""
+    if isinstance(schema, str):
+        dd_sequence = _get_dd_sequence_from_schema_name(schema)
+    else:
+        _validate_dd_sequence(schema)
+        dd_sequence = schema
+    return dd_sequence
+
+
+@transformer_api.transformer
+def add_dynamical_decoupling(
+    circuit: 'cirq.AbstractCircuit',
+    *,
+    context: Optional['cirq.TransformerContext'] = None,
+    schema: Union[str, Sequence['cirq.Gate']] = 'X_XINV',
+) -> 'cirq.Circuit':
+    """Adds dynamical decoupling gate operations to idle moments of a given circuit.
+    This transformer preserves the moment structure of the circuit.
+
+    Args:
+          circuit: Input circuit to transform.
+          context: `cirq.TransformerContext` storing common configurable options for transformers.
+          schema: Dynamical decoupling schema name or a dynamical decoupling sequence.
+            If a schema is specified, provided dynamical decouping sequence will be used.
+            Otherwise, customized dynamical decoupling sequence will be applied.
+
+    Returns:
+          A copy of the input circuit with dynamical decoupling operations.
+    """
+    last_busy_moment_by_qubits: Dict['cirq.Qid', int] = {q: 0 for q in circuit.all_qubits()}
+    insert_into: list[Tuple[int, 'cirq.OP_TREE']] = []
+
+    base_dd_sequence = _parse_dd_sequence(schema)
+
+    for moment_id, moment in enumerate(circuit):
+        for q in moment.qubits:
+            insert_gates = _repeat_sequence(
+                base_dd_sequence, num_idle_moments=moment_id - last_busy_moment_by_qubits[q] - 1
+            )
+            for idx, gate in enumerate(insert_gates):
+                insert_into.append((last_busy_moment_by_qubits[q] + idx + 1, gate.on(q)))
+            last_busy_moment_by_qubits[q] = moment_id
+
+    updated_circuit = circuit.unfreeze(copy=True)
+    updated_circuit.batch_insert_into(insert_into)
+    return updated_circuit

cirq-core/cirq/transformers/dynamical_decoupling_test.py

@@ -0,0 +1,123 @@
+# Copyright 2024 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.
+
+from typing import Sequence, Union
+import cirq
+from cirq import add_dynamical_decoupling
+import pytest
+
+
+def assert_dd(
+    input_circuit: cirq.Circuit,
+    expected_circuit: cirq.Circuit,
+    schema: Union[str, Sequence['cirq.Gate']],
+):
+    updated_circuit = add_dynamical_decoupling(input_circuit, schema=schema)
+    cirq.testing.assert_same_circuits(updated_circuit, expected_circuit)
+
+
+def test_no_insert_due_to_no_consecutive_moments():
+    a = cirq.NamedQubit('a')
+    b = cirq.NamedQubit('b')
+
+    # No insertion as there is no room for a dd sequence.
+    assert_dd(
+        input_circuit=cirq.Circuit(
+            cirq.Moment(cirq.H(a)), cirq.Moment(cirq.CNOT(a, b)), cirq.Moment(cirq.H(b))
+        ),
+        expected_circuit=cirq.Circuit(
+            cirq.Moment(cirq.H(a)), cirq.Moment(cirq.CNOT(a, b)), cirq.Moment(cirq.H(b))
+        ),
+        schema='XX_PAIR',
+    )
+
+
+@pytest.mark.parametrize(
+    'schema,inserted_gates',
+    [
+        ('XX_PAIR', (cirq.X, cirq.X)),
+        ('X_XINV', (cirq.X, cirq.X**-1)),
+        ('YY_PAIR', (cirq.Y, cirq.Y)),
+        ('Y_YINV', (cirq.Y, cirq.Y**-1)),
+    ],
+)
+def test_insert_provided_schema(schema: str, inserted_gates: Sequence['cirq.Gate']):
+    a = cirq.NamedQubit('a')
+    b = cirq.NamedQubit('b')
+    c = cirq.NamedQubit('c')
+
+    input_circuit = cirq.Circuit(
+        cirq.Moment(cirq.H(a)),
+        cirq.Moment(cirq.CNOT(a, b)),
+        cirq.Moment(cirq.CNOT(b, c)),
+        cirq.Moment(cirq.CNOT(b, c)),
+        cirq.Moment(cirq.measure_each(a, b, c)),
+    )
+    expected_circuit = cirq.Circuit(
+        cirq.Moment(cirq.H(a)),
+        cirq.Moment(cirq.CNOT(a, b)),
+        cirq.Moment(cirq.CNOT(b, c), inserted_gates[0](a)),
+        cirq.Moment(cirq.CNOT(b, c), inserted_gates[1](a)),
+        cirq.Moment(cirq.measure_each(a, b, c)),
+    )
+
+    # Insert one dynamical decoupling sequence in idle moments.
+    assert_dd(input_circuit, expected_circuit, schema=schema)
+
+
+def test_insert_by_customized_dd_sequence():
+    a = cirq.NamedQubit('a')
+    b = cirq.NamedQubit('b')
+    c = cirq.NamedQubit('c')
+
+    assert_dd(
+        input_circuit=cirq.Circuit(
+            cirq.Moment(cirq.H(a)),
+            cirq.Moment(cirq.CNOT(a, b)),
+            cirq.Moment(cirq.CNOT(b, c)),
+            cirq.Moment(cirq.CNOT(b, c)),
+            cirq.Moment(cirq.CNOT(b, c)),
+            cirq.Moment(cirq.CNOT(b, c)),
+            cirq.Moment(cirq.measure_each(a, b, c)),
+        ),
+        expected_circuit=cirq.Circuit(
+            cirq.Moment(cirq.H(a)),
+            cirq.Moment(cirq.CNOT(a, b)),
+            cirq.Moment(cirq.CNOT(b, c), cirq.X(a)),
+            cirq.Moment(cirq.CNOT(b, c), cirq.X(a)),
+            cirq.Moment(cirq.CNOT(b, c), cirq.Y(a)),
+            cirq.Moment(cirq.CNOT(b, c), cirq.Y(a)),
+            cirq.Moment(cirq.measure_each(a, b, c)),
+        ),
+        schema=[cirq.X, cirq.X, cirq.Y, cirq.Y],
+    )
+
+
+@pytest.mark.parametrize(
+    'schema,error_msg_regex',
+    [
+        ('INVALID_SCHEMA', 'Invalid schema name.'),
+        ([cirq.X], 'Invalid dynamical decoupling sequence. Expect more than one gates.'),
+        (
+            [cirq.X, cirq.H],
+            'Invalid dynamical decoupling sequence. Expect sequence production equals identity'
+            ' up to a global phase, got',
+        ),
+    ],
+)
+def test_invalid_dd_schema(schema: Union[str, Sequence['cirq.Gate']], error_msg_regex):
+    a = cirq.NamedQubit('a')
+    input_circuit = cirq.Circuit(cirq.H(a))
+    with pytest.raises(ValueError, match=error_msg_regex):
+        add_dynamical_decoupling(input_circuit, schema=schema)