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Sampler & Estimator

The Qiskit plugin provides OQSampler (SamplerV2) and OQEstimator (EstimatorV2) primitives that submit circuits to Open Quantum for execution.

OQSampler (SamplerV2)

OQSampler implements Qiskit's BaseSamplerV2 interface. It submits circuits to Open Quantum and returns measurement results as BitArray objects.

Creating a Sampler

Use service.create_sampler():

from openquantum_sdk.auth import ClientCredentials
from openquantum_sdk_qiskit import OpenQuantumService

service = OpenQuantumService(
    creds=ClientCredentials(
        client_id="s_your_client_id",
        client_secret="your_client_secret",
    ),
)

backend = service.return_backend("rigetti:cepheus-1-108q")

sampler = service.create_sampler(
    backend=backend,
    job_subcategory_id="phys:oth",  # Physics
    verbose=False,                  # default; True prints progress and credit cost
    job_timeout_seconds=86400,      # default, one day
)

verbose and job_timeout_seconds are the same on every Open Quantum plugin. Both default as above. Omit them to inherit the values already set on the backend from return_backend. create_estimator accepts the same two arguments. backend.run(..., verbose=, job_timeout_seconds=) overrides them for one submission.

Running the Sampler

from qiskit.circuit import QuantumCircuit

qc = QuantumCircuit(2, 2)
qc.h(0)
qc.cx(0, 1)
qc.measure([0, 1], [0, 1])

job = sampler.run([qc], shots=128)
result = job.result()

# Access the first pub result
pub_result = result[0]
bit_array = pub_result.data.meas
counts = bit_array.get_counts()
print(counts)

Expected output:

{'00': 507, '11': 517}

Shots Configuration

Specify shots per run:

job = sampler.run([qc], shots=4096)

If shots is not specified, it defaults to 100.

Parameter Binding

The sampler supports parameterized circuits with automatic binding:

from qiskit.circuit import QuantumCircuit, Parameter

theta = Parameter("theta")

qc = QuantumCircuit(1, 1)
qc.rx(theta, 0)
qc.measure(0, 0)

# Single parameter value
job = sampler.run([(qc, [0.5])], shots=128)

# Multiple parameter values
import numpy as np
values = np.linspace(0, np.pi, 5)
job = sampler.run([(qc, values.reshape(-1, 1))], shots=128)

Export Format

Control the QASM export format:

# Use OpenQASM 2 instead of the default OpenQASM 3
job = sampler.run([qc], shots=128, export_format="qasm2")

OQEstimator (EstimatorV2)

OQEstimator implements Qiskit's BaseEstimatorV2 interface. It computes expectation values of observables by delegating to Qiskit's BackendEstimatorV2 with an Open Quantum backend.

Creating an Estimator

estimator = service.create_estimator(
    backend=backend,
    job_subcategory_id="phys:oth",  # Physics
)

Running the Estimator

from qiskit.circuit import QuantumCircuit
from qiskit.quantum_info import SparsePauliOp

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

observable = SparsePauliOp("ZZ")

job = estimator.run([(qc, observable)], precision=0.01)
result = job.result()

print(f"Expectation value: {result[0].data.evs}")

Precision

The precision parameter controls the target precision for the expectation value estimate:

# Higher precision (more shots internally)
job = estimator.run([(qc, observable)], precision=0.001)

# Lower precision (fewer shots, faster)
job = estimator.run([(qc, observable)], precision=0.1)

Multiple Observables

obs_zz = SparsePauliOp("ZZ")
obs_xx = SparsePauliOp("XX")

job = estimator.run([
    (qc, obs_zz),
    (qc, obs_xx),
])
result = job.result()

print(f"<ZZ> = {result[0].data.evs}")
print(f"<XX> = {result[1].data.evs}")

Direct Construction

You can also construct the primitives directly without service.create_sampler() or service.create_estimator():

from openquantum_sdk_qiskit import OQSampler, OQEstimator

sampler = OQSampler(
    backend=backend,
    scheduler=service.scheduler,
    config={
        "backend_class_id": "rigetti:cepheus-1-108q",
        "job_subcategory_id": "phys:oth",  # Physics
    },
    export_format="qasm3",
)

estimator = OQEstimator(
    backend=backend,
    scheduler=service.scheduler,
    config={
        "backend_class_id": "rigetti:cepheus-1-108q",
        "job_subcategory_id": "phys:oth",  # Physics
    },
    export_format="qasm3",
)