Treat resilience_level=0 for EstimatorV2 properly

[t-imamichi]

Summary

EstimatorV2 applies TREX even if resilience_level is set 0 as follows.
This PR fixes the issue. The current code treat 0 as same as Unset. So, null will be delivered to the runtime server.

TODO:

• I'm wondering what kind of unit test to add. I need a help by experts.

from qiskit import QuantumCircuit
from qiskit.quantum_info import SparsePauliOp
from qiskit.transpiler.preset_passmanagers import generate_preset_pass_manager

from qiskit_ibm_runtime import QiskitRuntimeService, EstimatorV2, Session

circuit = QuantumCircuit(2)
circuit.h(0)
circuit.cx(0, 1)

obs = [SparsePauliOp("XY"), SparsePauliOp("YZ")]

service = QiskitRuntimeService()
backend = service.get_backend("ibm_kyiv")
pm = generate_preset_pass_manager(optimization_level=1, backend=backend)
isa_circuit = pm.run(circuit)
isa_obs = [ob.apply_layout(isa_circuit.layout) for ob in obs]

with Session(backend=backend) as session:
    estimator = EstimatorV2(session=session, backend=backend)
    jobs = []
    for lev in [0, 1]:
        estimator.options.resilience_level = lev
        jobs.append(estimator.run([(isa_circuit, isa_obs)]))
    results = [job.result() for job in jobs]

for level, result in enumerate(results):
    print('resilience_level', level)
    print(result[0].data.evs)
    print(result[0].metadata)
    print()

output

resilience_level 0
[ 0.0495992 -0.001002 ]
{'shots': 4096, 'target_precision': 0.015625, 'circuit_metadata': {}, 'resilience': {'twirled_readout_errors': [[0, 0.00439453125], [1, 0.00830078125]]}, 'num_randomizations': 32}
# TREX looks applied though resilience_level=0

resilience_level 1
[ 0.03233831 -0.01144279]
{'shots': 4096, 'target_precision': 0.015625, 'circuit_metadata': {}, 'resilience': {'twirled_readout_errors': [[0, 0.00146484375], [1, 0.0087890625]]}, 'num_randomizations': 32}

Details and comments

[coveralls]

Pull Request Test Coverage Report for Build 8369626913

Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 83.476%

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Totals
Change from base Build 8345950818:	0.0%
Covered Lines:	6163
Relevant Lines:	7383

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💛 - Coveralls

[chriseclectic]

Ah, good old None and 0 evaluating to False bugs

[kt474]

Replaced with #1542