[Python] Qiskit: AttributeError: 'ParameterExpression' object has no attribute 'name' when...

I am trying to optimize a quantum circuit using scipy.optimize.minimize and Qiskit Runtime's Estimator, running on an IBM Quantum real device. However, I am encountering the following error:

AttributeError: 'ParameterExpression' object has no attribute 'name'


The error occurs inside the minimize function call, specifically when `estimator.run() is executed in cost_func_estimator.

Here is the relevant code:

from scipy.optimize import minimize
from qiskit_ibm_runtime import Estimator, Session

objective_func_vals = []

with Session(backend=backend) as session:
estimator = Estimator(mode=session)
estimator.options.default_shots = 1000

estimator.options.dynamical_decoupling.enable = True
estimator.options.dynamical_decoupling.sequence_type = "XY4"
estimator.options.twirling.enable_gates = True
estimator.options.twirling.num_randomizations = "auto"

result = minimize(
cost_func_estimator,
init_params,
args=(candidate_circuit, qubitOp, estimator),
method="COBYLA",
tol=1e-2,
callback=callback,
)

save_progress(result.x, objective_func_vals, name_saved_file)
print(result)


The cost_func_estimator function is called within minimize and runs a job in the estimator:

def cost_func_estimator(params, ansatz, hamiltonian, estimator):
isa_hamiltonian = hamiltonian.apply_layout(ansatz.layout)
pub = (ansatz, isa_hamiltonian, params)

job = estimator.run([pub]) # The error occurs here

results = job.result()[0]
cost = results.data.evs
return cost


I expected scipy.optimize.minimize to optimize the parameters of my quantum circuit using Qiskit Runtime’s Estimator on an IBM Quantum real device.

I tried:

- Ensuring `init_params` contains only numerical values, not `ParameterExpression`.
- Using `bind_parameters()` to assign values before optimization.
- Updating `qiskit` and `qiskit-ibm-runtime` to the latest version.


Despite these attempts, the error persists. I expected estimator.run() to execute without issues, but it fails with AttributeError: 'ParameterExpression' object has no attribute 'name'.

How can I resolve this issue?

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