Add SSV3 for parameter table serialization

samplomatic/serialization/__init__.py

@@ -54,7 +54,9 @@
      - Added :class:`~.C1Register` serialization; updated :class:`~.BasisChange` format.
    * - 3
      - 0.16.0
-     - Added :class:`~.BalancedUniformPauli` distribution support in twirl nodes.
+     - Added :class:`~.BalancedUniformPauli` distribution support in twirl nodes; switched
+       parameter expression table serialization from circuit-wrapped QPY to direct
+       ``write_values``/``read_values``.
 
 Backwards compatibility
 ^^^^^^^^^^^^^^^^^^^^^^^

samplomatic/serialization/parameter_expression_serializer.py

@@ -30,6 +30,7 @@ class ParameterExpressionTableSerializer(TypeSerializer[ParameterExpressionTable
 
     class SSV1(DataSerializer[ParameterExpressionTable]):
         MIN_SSV = 1
+        MAX_SSV = 2
 
         @classmethod
         def serialize(cls, obj, ssv):
@@ -55,3 +56,29 @@ def deserialize(cls, data):
             for instr in circuit:
                 param_table.append(instr.operation.params[0])
             return param_table
+
+    class SSV3(DataSerializer[ParameterExpressionTable]):
+        MIN_SSV = 3
+
+        @classmethod
+        def serialize(cls, obj, ssv):
+            from qiskit._accelerate import qpy as qpy_rust
+            from qiskit.qpy.common import QPY_VERSION
+
+            with io.BytesIO() as buf:
+                qpy_rust.write_values(buf, list(obj._expressions))  # noqa: SLF001
+                values_base64 = pybase64.b64encode_as_string(buf.getvalue())
+
+            return {"qpy": str(QPY_VERSION), "values_base64": values_base64}
+
+        @classmethod
+        def deserialize(cls, data):
+            from qiskit._accelerate import qpy as qpy_rust
+
+            with io.BytesIO(pybase64.b64decode(data["values_base64"])) as buf:
+                expressions = qpy_rust.read_values(buf)
+
+            param_table = ParameterExpressionTable()
+            for expr in expressions:
+                param_table.append(expr)
+            return param_table

test/performance/test_serialization.py

@@ -1,6 +1,6 @@
 # This code is a Qiskit project.
 #
-# (C) Copyright IBM 2025.
+# (C) Copyright IBM 2025, 2026.
 #
 # 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
@@ -21,6 +21,7 @@
 from .utils import make_layered_circuit
 
 
+@pytest.mark.parametrize("ssv", [2, 3])
 @pytest.mark.parametrize(
     ("num_qubits", "num_gates"),
     [
@@ -40,15 +41,17 @@
         ),
     ],
 )
-def test_serialize_noisy_circuit(rng, benchmark, num_qubits, num_gates):
+def test_serialize_noisy_circuit(rng, benchmark, num_qubits, num_gates, ssv):
     """Test the speed of serializing a samplex."""
     num_boxes = num_gates // (num_qubits // 2)
     circuit = make_layered_circuit(num_qubits, num_boxes, inject_noise=True)
 
     _, samplex = build(circuit)
-    benchmark(samplex_to_json, samplex)
+    result = benchmark(samplex_to_json, samplex, ssv=ssv)
+    benchmark.extra_info["payload_bytes"] = len(result)
 
 
+@pytest.mark.parametrize("ssv", [2, 3])
 @pytest.mark.parametrize(
     ("num_qubits", "num_gates"),
     [
@@ -68,11 +71,12 @@ def test_serialize_noisy_circuit(rng, benchmark, num_qubits, num_gates):
         ),
     ],
 )
-def test_deserialize_noisy_circuit(rng, benchmark, num_qubits, num_gates):
+def test_deserialize_noisy_circuit(rng, benchmark, num_qubits, num_gates, ssv):
     """Test the speed of deserializing a samplex."""
     num_boxes = num_gates // (num_qubits // 2)
     circuit = make_layered_circuit(num_qubits, num_boxes, inject_noise=True)
 
     _, samplex = build(circuit)
-    samplex_json = samplex_to_json(samplex, None)
+    samplex_json = samplex_to_json(samplex, None, ssv=ssv)
+    benchmark.extra_info["payload_bytes"] = len(samplex_json)
     benchmark(samplex_from_json, samplex_json)

test/unit/test_serialization/test_parameter_expression_serializers.py

@@ -1,6 +1,6 @@
 # This code is a Qiskit project.
 #
-# (C) Copyright IBM 2025.
+# (C) Copyright IBM 2025, 2026.
 #
 # 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
@@ -29,3 +29,14 @@ def test_change_basis_serializer_round_trip(ssv):
     data = ParameterExpressionTableSerializer.serialize(table, ssv)
     orjson.dumps(data)
     assert table == TypeSerializer.deserialize(data)
+
+
+def test_ssv3_format():
+    """Test that SSV3 uses values_base64 (not circuit_base64) and includes qpy version."""
+    table = ParameterExpressionTable()
+    table.append(Parameter("x") + Parameter("y"))
+    data = ParameterExpressionTableSerializer.serialize(table, ssv=3)
+    assert "values_base64" in data
+    assert "circuit_base64" not in data
+    assert "qpy" in data
+    assert int(data["qpy"]) > 0