Add CompressDurationTag (#7543)

- This tag will signal the compiler to remove operations of zero
duration.
- Normally, these operations would have the same duration as their
typical gate (i.e. X**0 waits for the length of an X gate).
- Also adds JSON and cirq_google serialization for this tag.

Author: dstrain115

cirq-google/cirq_google/__init__.py

@@ -56,6 +56,7 @@
     AnalogDetuneCouplerOnly as AnalogDetuneCouplerOnly,
     AnalogDetuneQubit as AnalogDetuneQubit,
     CalibrationTag as CalibrationTag,
+    CompressDurationTag as CompressDurationTag,
     Coupler as Coupler,
     FSimGateFamily as FSimGateFamily,
     FSimViaModelTag as FSimViaModelTag,

cirq-google/cirq_google/api/v2/program.proto

@@ -347,6 +347,9 @@ message Tag {
 
     // Calibration Tag
     CalibrationTag calibration_tag = 9;
+    
+    // Compress duration to zero, if possible.
+    CompressDurationTag compress_duration = 10;
 
     // Catch-all for all gates that do not fit into the
     // above tags.
@@ -392,6 +395,10 @@ message CalibrationTag {
   string token = 1;
 }
 
+// Tag to specify that hardware should compress the duration to zero
+// if possible.  For instance, in X**0 or PhasedXZGate with zero angles.
+message CompressDurationTag {}
+
 // Tag to represent any internal tags or tags not yet
 // implemented in the proto.
 message InternalTag {

cirq-google/cirq_google/api/v2/program_pb2.py

@@ -49,6 +49,7 @@ def _old_xmon(*args, **kwargs):
         'Calibration': cirq_google.Calibration,
         'CalibrationTag': cirq_google.CalibrationTag,
         'CalibrationLayer': cirq_google.CalibrationLayer,
+        'CompressDurationTag': cirq_google.CompressDurationTag,
         'CouplerPulse': cirq_google.experimental.CouplerPulse,
         'Coupler': cirq_google.Coupler,
         'GoogleNoiseProperties': cirq_google.GoogleNoiseProperties,

cirq-google/cirq_google/api/v2/program_pb2.pyi

@@ -0,0 +1,3 @@
+{
+      "cirq_type": "CompressDurationTag"
+}

cirq-google/cirq_google/json_resolver_cache.py

@@ -0,0 +1 @@
+cirq_google.CompressDurationTag()

cirq-google/cirq_google/json_test_data/CompressDurationTag.json

@@ -20,6 +20,8 @@
 
 from cirq_google.ops.calibration_tag import CalibrationTag as CalibrationTag
 
+from cirq_google.ops.compress_duration_tag import CompressDurationTag as CompressDurationTag
+
 from cirq_google.ops.coupler import Coupler as Coupler
 
 from cirq_google.ops.fsim_gate_family import FSimGateFamily as FSimGateFamily

cirq-google/cirq_google/json_test_data/CompressDurationTag.repr

@@ -0,0 +1,65 @@
+# Copyright 2025 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.
+
+"""A class that can be used to denote a physical Z gate."""
+
+from __future__ import annotations
+
+from typing import Any
+
+import cirq
+from cirq_google.api.v2 import program_pb2
+
+
+class CompressDurationTag:
+    """Class to direct hardware to compress operations of zero duration.
+
+    By default, parameters of gates that could lead to no-ops do not
+    change the original duration of the gate.  For instance, X**0
+    will cause a wait of the same duration as an X gate.  (This is so
+    that parameter sweeps do not inadvertently change the duration of
+    the circuit, leading to artifacts in data).
+
+    When applied to an operation, this will cause the operation to
+    compress to zero duration if possible.  Currently, this will affect
+    gates with angles of zero.
+
+    This can also affect PhasedXZGates to turn them into virtual Z gates
+    if the resulting gate has a Z phase but no X component.
+    """
+
+    def __str__(self) -> str:
+        return 'CompressDurationTag()'
+
+    def __repr__(self) -> str:
+        return 'cirq_google.CompressDurationTag()'
+
+    def _json_dict_(self) -> dict[str, Any]:
+        return cirq.obj_to_dict_helper(self, [])
+
+    def __eq__(self, other) -> bool:
+        return isinstance(other, CompressDurationTag)
+
+    def __hash__(self) -> int:
+        return 456789
+
+    def to_proto(self, msg: program_pb2.Tag | None = None) -> program_pb2.Tag:
+        if msg is None:
+            msg = program_pb2.Tag()
+        msg.compress_duration.SetInParent()
+        return msg
+
+    @staticmethod
+    def from_proto(msg: program_pb2.Tag) -> CompressDurationTag:
+        return CompressDurationTag()

cirq-google/cirq_google/ops/__init__.py

@@ -0,0 +1,37 @@
+# Copyright 2025 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 __future__ import annotations
+
+import cirq
+import cirq_google
+
+
+def test_equality():
+    assert cirq_google.CompressDurationTag() == cirq_google.CompressDurationTag()
+    assert hash(cirq_google.CompressDurationTag()) == hash(cirq_google.CompressDurationTag())
+
+
+def test_syc_str_repr():
+    assert str(cirq_google.CompressDurationTag()) == 'CompressDurationTag()'
+    assert repr(cirq_google.CompressDurationTag()) == 'cirq_google.CompressDurationTag()'
+    cirq.testing.assert_equivalent_repr(
+        cirq_google.CompressDurationTag(), setup_code=('import cirq\nimport cirq_google\n')
+    )
+
+
+def test_proto():
+    tag = cirq_google.CompressDurationTag()
+    msg = tag.to_proto()
+    assert tag == cirq_google.CompressDurationTag.from_proto(msg)