BasicAer fails when shots requested exceeds a threshold

Environment

• Qiskit Terra version: 371a2bc2171c6b610c7aa56d60b51f45a0fa7bad
• Python version: 3.9.10
• Operating system: Arch Linux

What is happening?

The BasicAer simulator is failing when the number of shots exceeds some threshold.

How can we reproduce the issue?

from qiskit import BasicAer, QuantumCircuit

backend = BasicAer.get_backend('statevector_simulator')
circuit = QuantumCircuit(1)
circuit.x(0)
backend.run(circuit, shots=100000)

Output:

---------------------------------------------------------------------------
QiskitError                               Traceback (most recent call last)
Input In [1], in <module>
      4 circuit = QuantumCircuit(1)
      5 circuit.x(0)
----> 6 backend.run(circuit, shots=100000)

File ~/projects/qiskit-terra/qiskit/providers/basicaer/qasm_simulator.py:409, in QasmSimulatorPy.run(self, qobj, **backend_options)
    407         else:
    408             out_options[key] = backend_options[key]
--> 409     qobj = assemble(qobj, self, **out_options)
    410     qobj_options = qobj.config
    411 else:

File ~/projects/qiskit-terra/qiskit/compiler/assembler.py:172, in assemble(experiments, backend, qobj_id, qobj_header, shots, memory, max_credits, seed_simulator, qubit_lo_freq, meas_lo_freq, qubit_lo_range, meas_lo_range, schedule_los, meas_level, meas_return, meas_map, memory_slot_size, rep_time, rep_delay, parameter_binds, parametric_pulses, init_qubits, **run_config)
    170 experiments = experiments if isinstance(experiments, list) else [experiments]
    171 pulse_qobj = any(isinstance(exp, (ScheduleBlock, Schedule, Instruction)) for exp in experiments)
--> 172 qobj_id, qobj_header, run_config_common_dict = _parse_common_args(
    173     backend,
    174     qobj_id,
    175     qobj_header,
    176     shots,
    177     memory,
    178     max_credits,
    179     seed_simulator,
    180     init_qubits,
    181     rep_delay,
    182     qubit_lo_freq,
    183     meas_lo_freq,
    184     qubit_lo_range,
    185     meas_lo_range,
    186     schedule_los,
    187     pulse_qobj=pulse_qobj,
    188     **run_config,
    189 )
    191 # assemble either circuits or schedules
    192 if all(isinstance(exp, QuantumCircuit) for exp in experiments):

File ~/projects/qiskit-terra/qiskit/compiler/assembler.py:327, in _parse_common_args(backend, qobj_id, qobj_header, shots, memory, max_credits, seed_simulator, init_qubits, rep_delay, qubit_lo_freq, meas_lo_freq, qubit_lo_range, meas_lo_range, schedule_los, pulse_qobj, **run_config)
    325     raise QiskitError("Argument 'shots' should be of type 'int'")
    326 elif max_shots and max_shots < shots:
--> 327     raise QiskitError(
    328         "Number of shots specified: %s exceeds max_shots property of the "
    329         "backend: %s." % (shots, max_shots)
    330     )
    332 dynamic_reprate_enabled = getattr(backend_config, "dynamic_reprate_enabled", False)
    333 if dynamic_reprate_enabled:

QiskitError: 'Number of shots specified: 100000 exceeds max_shots property of the backend: 65536.'

What should happen?

BasicAer should not have a shot limit.

Any suggestions?

No response

[mtreinish]

In backendv2 you don’t have to define a limit, it’s validated in the Options object’s validators when you try to update the value. If you don’t set a validator it doesn’t check anything and any value can be used. But yeah in BackendV1 it is a required integer field in the BackendConfiguration

[kevinsung]

It should be fixed by https://github.com/Qiskit/qiskit-terra/pull/7801. @alejomonbar please add the line “Fixes #7634” to the opening post there.