Fix handling of circuit metadata

qiskit/providers/aer/backends/aerbackend.py

@@ -288,9 +288,30 @@ def _run(self, qobj, job_id='', format_result=True):
         # Start timer
         start = time.time()
 
+        # Take metadata from headers of experiments to work around JSON serialization error
+        metadata_list = []
+        metadata_index = 0
+        for expr in qobj.experiments:
+            if hasattr(expr.header, "metadata"):
+                metadata_copy = expr.header.metadata.copy()
+                metadata_list.append(metadata_copy)
+                expr.header.metadata.clear()
+                if "id" in metadata_copy:
+                    expr.header.metadata["id"] = metadata_copy["id"]
+                expr.header.metadata["metadata_index"] = metadata_index
+                metadata_index += 1
+
         # Run simulation
         output = self._execute(qobj)
 
+        # Recover metadata
+        metadata_index = 0
+        for expr in qobj.experiments:
+            if hasattr(expr.header, "metadata"):
+                expr.header.metadata.clear()
+                expr.header.metadata.update(metadata_list[metadata_index])
+                metadata_index += 1
+
         # Validate output
         if not isinstance(output, dict):
             logger.error("%s: simulation failed.", self.name())
@@ -305,6 +326,14 @@ def _run(self, qobj, job_id='', format_result=True):
         output["backend_name"] = self.name()
         output["backend_version"] = self.configuration().backend_version
 
+        # Push metadata to experiment headers
+        for result in output["results"]:
+            if ("header" in result and
+                    "metadata" in result["header"] and
+                    "metadata_index" in result["header"]["metadata"]):
+                metadata_index = result["header"]["metadata"]["metadata_index"]
+                result["header"]["metadata"] = metadata_list[metadata_index]
+
         # Add execution time
         output["time_taken"] = time.time() - start
 

releasenotes/notes/remove_circuit_metadata_from_qobj-324e7ea9b369ee67.yaml

@@ -0,0 +1,13 @@
+---
+fixes:
+  - |
+    Fixed a potential issue with running simulations on circuits that have the
+    :attr:`.QuantumCircuit.metadata` attribute set. The :attr:`~.QuantumCircuit.metadata`
+    attribute can be any python dictionary and previously qiskit-aer would attempt to
+    JSON serialize the contents of the attribute to process it with the rest of the rest
+    of the circuit input, even if the contents were not JSON serializable. This no longer
+    occurs as the :attr:`.QuantumCircuit.metadata`  attribute is not used to run the
+    simulation so now the contents are no serialized and instead are directly attached
+    to the :class:`qiskit.result.Result` object without attempting to JSON serialize
+    the contents.
+    Fixed `#1435 <https://github.com/Qiskit/qiskit-aer/issues/1435>`__

test/terra/backends/aer_simulator/test_metadata.py

@@ -0,0 +1,104 @@
+# This code is part of Qiskit.
+#
+# (C) Copyright IBM 2018, 2019, 2020, 2021, 2022.
+#
+# 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
+# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
+#
+# Any modifications or derivative works of this code must retain this
+# copyright notice, and modified files need to carry a notice indicating
+# that they have been altered from the originals.
+"""
+AerSimulator Integration Tests
+"""
+from math import sqrt
+from ddt import ddt
+from qiskit import transpile, QuantumCircuit
+from test.terra.reference import ref_algorithms
+
+from test.terra.backends.simulator_test_case import (
+    SimulatorTestCase, supported_methods)
+
+
+@ddt
+class TestMetadata(SimulatorTestCase):
+    """AerSimulator algorithm tests in the default basis"""
+
+    @supported_methods(
+        ['automatic', 'statevector', 'density_matrix',
+         'matrix_product_state', 'extended_stabilizer'])
+    def test_single_circuit_metadata(self, method, device):
+        """Test circuits with object metadata."""
+        backend = self.backend(method=method, device=device)
+        metadata = {1: object}
+        circuit = QuantumCircuit(1, name='circ0', metadata=metadata.copy())
+        result = backend.run(circuit).result()
+        self.assertSuccess(result)
+        self.assertEqual(result.results[0].header.metadata, metadata)
+        self.assertEqual(circuit.metadata, metadata)
+
+    @supported_methods(
+        ['automatic', 'statevector', 'density_matrix',
+         'matrix_product_state', 'extended_stabilizer'])
+    def test_three_circuit_metadata(self, method, device):
+        """Test circuits with object metadata."""
+        backend = self.backend(method=method, device=device)
+
+        metadata0 = {0: object}
+        circuit0 = QuantumCircuit(1, name='circ0', metadata=metadata0.copy())
+
+        metadata1 = {1: object}
+        circuit1 = QuantumCircuit(1, name='circ1', metadata=metadata1.copy())
+
+        metadata2 = {2: object}
+        circuit2 = QuantumCircuit(1, name='circ2', metadata=metadata2.copy())
+
+        result = backend.run([circuit0, circuit1, circuit2]).result()
+        self.assertSuccess(result)
+        self.assertEqual(len(result.results), 3)
+        self.assertEqual(result.results[0].header.metadata, metadata0)
+        self.assertEqual(result.results[1].header.metadata, metadata1)
+        self.assertEqual(result.results[2].header.metadata, metadata2)
+        self.assertEqual(circuit0.metadata, metadata0)
+        self.assertEqual(circuit1.metadata, metadata1)
+        self.assertEqual(circuit2.metadata, metadata2)
+
+    @supported_methods(
+        ['automatic', 'statevector', 'density_matrix', 'matrix_product_state'])
+    def test_three_parameterized_circuit_metadata(self, method, device):
+        """Test circuits with object metadata."""
+        backend = self.backend(method=method, device=device)
+
+        metadata0 = {0: object}
+        circuit0 = QuantumCircuit(1, name='circ0', metadata=metadata0.copy())
+        circuit0.ry(0.1, 0)
+        circuit0.measure_all()
+
+        metadata1 = {1: object}
+        circuit1 = QuantumCircuit(1, name='circ1', metadata=metadata1.copy())
+        circuit1.ry(0.1, 0)
+        circuit1.measure_all()
+
+        metadata2 = {2: object}
+        circuit2 = QuantumCircuit(1, name='circ2', metadata=metadata2.copy())
+        circuit2.ry(0.1, 0)
+        circuit2.measure_all()
+
+        parameterizations=[[[[0, 0], [0, 1]]],
+                           [[[0, 0], [0, 1, 2]]],
+                           []]
+
+        result = backend.run([circuit0, circuit1, circuit2],
+                             parameterizations=parameterizations).result()
+        self.assertSuccess(result)
+        self.assertEqual(len(result.results), 6)
+        self.assertEqual(result.results[0].header.metadata, metadata0)
+        self.assertEqual(result.results[1].header.metadata, metadata0)
+        self.assertEqual(result.results[2].header.metadata, metadata1)
+        self.assertEqual(result.results[3].header.metadata, metadata1)
+        self.assertEqual(result.results[4].header.metadata, metadata1)
+        self.assertEqual(result.results[5].header.metadata, metadata2)
+        self.assertEqual(circuit0.metadata, metadata0)
+        self.assertEqual(circuit1.metadata, metadata1)
+        self.assertEqual(circuit2.metadata, metadata2)