Add ZXTransformer contrib module

cirq-core/cirq/contrib/__init__.py

@@ -24,3 +24,4 @@
 from cirq.contrib.qcircuit import circuit_to_latex_using_qcircuit as circuit_to_latex_using_qcircuit
 from cirq.contrib import json  # noqa: F401
 from cirq.contrib.circuitdag import CircuitDag as CircuitDag, Unique as Unique
+from cirq.contrib.zxtransformer import zx_transformer as zx_transformer  # noqa: F401

cirq-core/cirq/contrib/requirements.txt

@@ -6,3 +6,6 @@ pylatex~=1.4
 # quimb
 quimb~=1.8
 opt_einsum
+
+# required for zxtransformer
+pyzx>=0.10.0

cirq-core/cirq/contrib/zxtransformer/__init__.py

@@ -0,0 +1,18 @@
+# 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.
+
+"""A custom transformer for Cirq which uses ZX-Calculus for circuit optimization, implemented using
+PyZX."""
+
+from cirq.contrib.zxtransformer.zxtransformer import zx_transformer