QPY serialization of ParameterExpression throws error #13879
Description
- Qiskit version: 1.3.2
- qiskit-ibm-runtime version: 0.36.1
- Python version: 3.12
Certain ParameterExpressions cause QPY serialization v13 to throw. QPY v12 does not throw.
Note
After opening this issue I found the following much simpler script for triggering the bug:
from qiskit.circuit import Parameter, ParameterExpression
from qiskit import qpy
a = Parameter("a")
b = Parameter("b")
a1 = a * 2
a2 = a1.subs({a: 2 * b})
qpy.binary_io.value.dumps_value(a2, version=13);There is no error with QPY version 12.
When running the script above, the error,
AttributeError: 'ParameterExpression' object has no attribute 'name'is thrown here at line 40
qiskit/qiskit/qpy/binary_io/value.py
Lines 39 to 42 in d9b8a18
I tried to track down the problem, which is centered on _qpy_replay. But there are no documentation or comments describing _qpy_replay and several adjacent structures and functions.
Note
The following script is not a minimal description of the bug. But it is an example abstracted from using EstimatorQNN and NeuralNetworkClassifier from qiskit-machine-learning on a real IBM device (in this case, ibm_kyiv). It's unlikely that simple workflows involving EstimatorQNN will work when this bug is present.
Running this script will trigger the bug:
from qiskit.circuit.library import ZZFeatureMap, RealAmplitudes
from qiskit import QuantumCircuit
from qiskit_ibm_runtime import fake_provider
from qiskit.transpiler.preset_passmanagers import generate_preset_pass_manager
def make_circuit():
n_qubits = 2
reps = 1
feature_map = ZZFeatureMap(feature_dimension=n_qubits, reps=reps)
ansatz = RealAmplitudes(num_qubits=n_qubits, reps=reps)
qc = QuantumCircuit(n_qubits)
qc.compose(feature_map, inplace=True)
qc.compose(ansatz, inplace=True)
backend = fake_provider.FakeKyiv()
pm = generate_preset_pass_manager(backend=backend, optimization_level=1)
isa_qc = pm.run(qc)
return isa_qc
from qiskit import qpy
isa_qc = make_circuit()
qpy.binary_io.value.dumps_value(isa_qc.global_phase, version=13);If I replace versions=13 with version=12, I see no apparent problem.