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Reference implementation of Estimator and Sampler Primitives (Qiskit#7780)
* Merge pull request Qiskit#7651 from ikkoham/primitives/sampler-and-estimator * rename releasenote * add releasenote * move to qiskit/primitives * fix lint (cyclic import) * Update releasenotes/notes/primitives-fb4515ec0f4cbd8e.yaml Co-authored-by: Ali Javadi-Abhari <[email protected]> * fix sampler with empty parameters Co-authored-by: Ali Javadi-Abhari <[email protected]> Co-authored-by: Takashi Imamichi <[email protected]>
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‎qiskit/primitives/__init__.py‎

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:toctree: ../stubs/
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BaseEstimator
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Estimator
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Sampler
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=======
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:toctree: ../stubs/
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BaseSampler
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Sampler
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Results
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=======
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from .base_estimator import BaseEstimator
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from .base_sampler import BaseSampler
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from .estimator import Estimator
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from .estimator_result import EstimatorResult
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from .sampler import Sampler
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from .sampler_result import SamplerResult

‎qiskit/primitives/estimator.py‎

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# This code is part of Qiskit.
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#
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# (C) Copyright IBM 2022.
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#
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# This code is licensed under the Apache License, Version 2.0. You may
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# obtain a copy of this license in the LICENSE.txt file in the root directory
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# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
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#
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# Any modifications or derivative works of this code must retain this
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# copyright notice, and modified files need to carry a notice indicating
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# that they have been altered from the originals.
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"""
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Estimator class
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"""
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from __future__ import annotations
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from collections.abc import Iterable, Sequence
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from typing import cast
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import numpy as np
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from qiskit.circuit import Parameter, QuantumCircuit
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from qiskit.exceptions import QiskitError
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from qiskit.opflow import PauliSumOp
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from qiskit.quantum_info import Statevector
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from qiskit.quantum_info.operators.base_operator import BaseOperator
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from .base_estimator import BaseEstimator
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from .estimator_result import EstimatorResult
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from .utils import init_circuit, init_observable
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class Estimator(BaseEstimator):
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"""
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Estimator class
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"""
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def __init__(
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self,
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circuits: QuantumCircuit | Iterable[QuantumCircuit],
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observables: BaseOperator | PauliSumOp | Iterable[BaseOperator | PauliSumOp],
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parameters: Iterable[Iterable[Parameter]] | None = None,
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):
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if isinstance(circuits, QuantumCircuit):
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circuits = [circuits]
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circuits = [init_circuit(circuit) for circuit in circuits]
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if isinstance(observables, (PauliSumOp, BaseOperator)):
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observables = [observables]
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observables = [init_observable(observable) for observable in observables]
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super().__init__(
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circuits=circuits,
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observables=observables,
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parameters=parameters,
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)
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self._is_closed = False
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def __call__(
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self,
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circuits: Sequence[int] | None = None,
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observables: Sequence[int] | None = None,
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parameters: Sequence[Sequence[float]] | Sequence[float] | None = None,
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**run_options,
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) -> EstimatorResult:
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if self._is_closed:
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raise QiskitError("The primitive has been closed.")
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if parameters and not isinstance(parameters[0], Sequence):
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parameters = cast("Sequence[float]", parameters)
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parameters = [parameters]
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if (
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circuits is None
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and len(self._circuits) == 1
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and observables is None
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and len(self._observables) == 1
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and parameters is not None
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):
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circuits = [0] * len(parameters)
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observables = [0] * len(parameters)
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if circuits is None:
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circuits = list(range(len(self._circuits)))
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if observables is None:
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observables = list(range(len(self._observables)))
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if parameters is None:
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parameters = [[]] * len(circuits)
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if len(circuits) != len(parameters):
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raise QiskitError(
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f"The number of circuits ({len(circuits)}) does not match "
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f"the number of parameter sets ({len(parameters)})."
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)
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bound_circuits = []
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for i, value in zip(circuits, parameters):
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if len(value) != len(self._parameters[i]):
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raise QiskitError(
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f"The number of values ({len(value)}) does not match "
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f"the number of parameters ({len(self._parameters[i])})."
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)
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bound_circuits.append(
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self._circuits[i].bind_parameters(dict(zip(self._parameters[i], value)))
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)
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sorted_observables = [self._observables[i] for i in observables]
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expectation_values = []
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for circ, obs in zip(bound_circuits, sorted_observables):
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if circ.num_qubits != obs.num_qubits:
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raise QiskitError(
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f"The number of qubits of a circuit ({circ.num_qubits}) does not match "
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f"the number of qubits of a observable ({obs.num_qubits})."
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)
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expectation_values.append(Statevector(circ).expectation_value(obs))
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return EstimatorResult(np.real_if_close(expectation_values), [])
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def close(self):
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self._is_closed = True

‎qiskit/primitives/sampler.py‎

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# This code is part of Qiskit.
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#
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# (C) Copyright IBM 2022.
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#
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# This code is licensed under the Apache License, Version 2.0. You may
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# obtain a copy of this license in the LICENSE.txt file in the root directory
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# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
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#
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# Any modifications or derivative works of this code must retain this
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# copyright notice, and modified files need to carry a notice indicating
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# that they have been altered from the originals.
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"""
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Sampler class
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"""
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from __future__ import annotations
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from collections.abc import Iterable, Sequence
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from qiskit.circuit import Parameter, QuantumCircuit
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from qiskit.exceptions import QiskitError
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from qiskit.quantum_info import Statevector
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from qiskit.result import QuasiDistribution
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from .base_sampler import BaseSampler
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from .sampler_result import SamplerResult
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from .utils import final_measurement_mapping, init_circuit
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class Sampler(BaseSampler):
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"""
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Sampler class
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"""
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def __init__(
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self,
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circuits: QuantumCircuit | Iterable[QuantumCircuit],
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parameters: Iterable[Iterable[Parameter]] | None = None,
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):
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"""
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Args:
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circuits: circuits to be executed
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Raises:
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QiskitError: if some classical bits are not used for measurements.
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"""
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if isinstance(circuits, QuantumCircuit):
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circuits = [circuits]
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circuits = [init_circuit(circuit) for circuit in circuits]
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q_c_mappings = [final_measurement_mapping(circuit) for circuit in circuits]
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self._qargs_list = []
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for circuit, q_c_mapping in zip(circuits, q_c_mappings):
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if set(range(circuit.num_clbits)) != set(q_c_mapping.values()):
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raise QiskitError(
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"some classical bits are not used for measurements."
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f" the number of classical bits {circuit.num_clbits},"
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f" the used classical bits {set(q_c_mapping.values())}."
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)
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c_q_mapping = sorted((c, q) for q, c in q_c_mapping.items())
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self._qargs_list.append([q for _, q in c_q_mapping])
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circuits = [circuit.remove_final_measurements(inplace=False) for circuit in circuits]
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super().__init__(circuits, parameters)
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self._is_closed = False
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def __call__(
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self,
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circuits: Sequence[int] | None = None,
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parameters: Sequence[Sequence[float]] | None = None,
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**run_options,
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) -> SamplerResult:
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if self._is_closed:
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raise QiskitError("The primitive has been closed.")
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if circuits is None and parameters is not None and len(self._circuits) == 1:
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circuits = [0] * len(parameters)
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if circuits is None:
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circuits = list(range(len(self._circuits)))
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if parameters is None:
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parameters = [[]] * len(circuits)
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if len(circuits) != len(parameters):
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raise QiskitError(
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f"The number of circuits ({len(circuits)}) does not match "
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f"the number of parameter sets ({len(parameters)})."
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)
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bound_circuits_qargs = []
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for i, value in zip(circuits, parameters):
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if len(value) != len(self._parameters[i]):
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raise QiskitError(
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f"The number of values ({len(value)}) does not match "
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f"the number of parameters ({len(self._parameters[i])})."
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)
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bound_circuits_qargs.append(
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(
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self._circuits[i].bind_parameters(dict(zip(self._parameters[i], value))),
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self._qargs_list[i],
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)
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)
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probabilities = [
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Statevector(circ).probabilities(qargs=qargs) for circ, qargs in bound_circuits_qargs
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]
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quasis = [QuasiDistribution(dict(enumerate(p))) for p in probabilities]
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return SamplerResult(quasis, [{}] * len(circuits))
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def close(self):
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self._is_closed = True

‎qiskit/primitives/utils.py‎

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# This code is part of Qiskit.
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#
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# (C) Copyright IBM 2022.
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#
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# This code is licensed under the Apache License, Version 2.0. You may
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# obtain a copy of this license in the LICENSE.txt file in the root directory
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# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
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#
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# Any modifications or derivative works of this code must retain this
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# copyright notice, and modified files need to carry a notice indicating
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# that they have been altered from the originals.
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"""
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Utility functions for primitives
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"""
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from __future__ import annotations
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from qiskit.circuit import ParameterExpression, QuantumCircuit
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from qiskit.extensions.quantum_initializer.initializer import Initialize
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from qiskit.opflow import PauliSumOp
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from qiskit.quantum_info import SparsePauliOp, Statevector
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from qiskit.quantum_info.operators.base_operator import BaseOperator
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def init_circuit(state: QuantumCircuit | Statevector) -> QuantumCircuit:
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"""Initialize state."""
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if isinstance(state, QuantumCircuit):
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return state
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if not isinstance(state, Statevector):
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state = Statevector(state)
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qc = QuantumCircuit(state.num_qubits)
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qc.append(Initialize(state), qargs=range(state.num_qubits))
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return qc
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def init_observable(observable: BaseOperator | PauliSumOp) -> SparsePauliOp:
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"""Initialize observable"""
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if isinstance(observable, SparsePauliOp):
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return observable
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if isinstance(observable, PauliSumOp):
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if isinstance(observable.coeff, ParameterExpression):
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raise TypeError(
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f"observable must have numerical coefficient, not {type(observable.coeff)}"
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)
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return observable.coeff * observable.primitive
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if isinstance(observable, BaseOperator):
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return SparsePauliOp.from_operator(observable)
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return SparsePauliOp(observable)
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def final_measurement_mapping(circuit: QuantumCircuit) -> dict[int, int]:
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"""Return the final measurement mapping for the circuit.
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Dict keys label measured qubits, whereas the values indicate the
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classical bit onto which that qubits measurement result is stored.
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Note: this function is a slightly simplified version of a utility function
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``_final_measurement_mapping`` of
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`mthree <https://github.com/Qiskit-Partners/mthree>`_.
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Parameters:
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circuit: Input Qiskit QuantumCircuit.
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Returns:
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Mapping of qubits to classical bits for final measurements.
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"""
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active_qubits = list(range(circuit.num_qubits))
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active_cbits = list(range(circuit.num_clbits))
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# Find final measurements starting in back
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mapping = {}
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for item in circuit._data[::-1]:
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if item[0].name == "measure":
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cbit = circuit.find_bit(item[2][0]).index
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qbit = circuit.find_bit(item[1][0]).index
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if cbit in active_cbits and qbit in active_qubits:
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mapping[qbit] = cbit
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active_cbits.remove(cbit)
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active_qubits.remove(qbit)
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elif item[0].name != "barrier":
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for qq in item[1]:
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_temp_qubit = circuit.find_bit(qq).index
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if _temp_qubit in active_qubits:
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active_qubits.remove(_temp_qubit)
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if not active_cbits or not active_qubits:
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break
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# Sort so that classical bits are in numeric order low->high.
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mapping = dict(sorted(mapping.items(), key=lambda item: item[1]))
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return mapping

‎releasenotes/notes/base_primitives-fb4515ec0f4cbd8e.yaml‎

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‎releasenotes/notes/primitives-fb4515ec0f4cbd8e.yaml‎

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---
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features:
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- |
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Added new abstract base primitive types under :mod:`qiskit.primitives`.
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There are two types of primitives, Sampler and Estimator.
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The reference implementation can be found in :mod:`qiskit.primitives`.
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Other concrete implementations will come from providers.

‎test/python/primitives/__init__.py‎

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# This code is part of Qiskit.
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#
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# (C) Copyright IBM 2022.
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#
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# This code is licensed under the Apache License, Version 2.0. You may
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# obtain a copy of this license in the LICENSE.txt file in the root directory
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# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
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#
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# Any modifications or derivative works of this code must retain this
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# copyright notice, and modified files need to carry a notice indicating
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# that they have been altered from the originals.
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"""Tests for the primitives."""

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