Source code for qiskit_experiments.library.characterization.local_readout_error

# This code is part of Qiskit.
#
# (C) Copyright IBM 2021, 2022.
#
# This code is licensed under the Apache License, Version 2.0. You may
# obtain a copy of this license in the LICENSE.txt file in the root directory
# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
#
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# copyright notice, and modified files need to carry a notice indicating
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"""
Local readout error calibration experiment class.
"""
from typing import Iterable, List, Optional
from qiskit import QuantumCircuit
from qiskit.providers.backend import BackendV2, Backend
from qiskit.exceptions import QiskitError
from qiskit_experiments.framework import BaseExperiment
from qiskit_experiments.library.characterization.analysis.local_readout_error_analysis import (
    LocalReadoutErrorAnalysis,
)
from .correlated_readout_error import calibration_circuit


[docs] class LocalReadoutError(BaseExperiment): r"""An experiment for characterizing local readout error. # section: overview This class constructs a :class:`~qiskit.result.LocalReadoutMitigator` containing a sequence of assignment matrices :math:`A` characterizing the readout error for the given qubits from the experiment results. The full assignment matrix is accessible via the :meth:`~qiskit.result.LocalReadoutMitigator.assignment_matrix` method. Readout errors affect quantum computation during the measurement of the qubits in a quantum device. By characterizing the readout errors, it is possible to construct a *readout error mitigator* that is used both to obtain a more accurate distribution of the outputs, and more accurate measurements of expectation value for measurables. The readout mitigator is generated from an *assignment matrix*: a :math:`2^n \times 2^n` matrix :math:`A` such that :math:`A_{y,x}` is the probability to observe :math:`y` given the true outcome should be :math:`x`. The assignment matrix is used to compute the *mitigation matrix* used in the readout error mitigation process itself. A *Local readout mitigator* works under the assumption that readout errors are mostly *local*, meaning readout errors for different qubits are independent of each other. In this case, the assignment matrix is the tensor product of :math:`n` :math:`2 \times 2` matrices, one for each qubit, making it practical to store the assignment matrix in implicit form, by storing the individual :math:`2 \times 2` assignment matrices. The corresponding class in Qiskit is the :class:`~qiskit.result.LocalReadoutMitigator` in :mod:`qiskit.result`. The experiment generates 2 circuits, corresponding to the states :math:`|0^n\rangle` and :math:`|1^n\rangle`, measuring the error in all the qubits at once, and constructs the assignment matrix and local mitigator from the results. See :class:`LocalReadoutErrorAnalysis` documentation for additional information on local readout error experiment analysis. # section: analysis_ref :class:`LocalReadoutErrorAnalysis` # section: example .. jupyter-execute:: :hide-code: # backend from qiskit_aer import AerSimulator from qiskit_ibm_runtime.fake_provider import FakePerth backend = AerSimulator.from_backend(FakePerth()) .. jupyter-execute:: from qiskit_experiments.library import LocalReadoutError qubits = list(range(4)) exp = LocalReadoutError(physical_qubits=qubits, backend=backend) exp.analysis.set_options(plot=True) exp.set_run_options(shots=10000) exp_data = exp.run().block_for_results() display(exp_data.figure(0)) exp_data.analysis_results(dataframe=True) # section: manual :doc:`/manuals/measurement/readout_mitigation` # section: reference .. ref_arxiv:: 1 2006.14044 """ def __init__( self, physical_qubits: Optional[Iterable[int]] = None, backend: Optional[Backend] = None, ): """Initialize a local readout error characterization experiment. Args: physical_qubits: Optional, the backend qubits being characterized for readout error. If None all qubits on the provided backend will be characterized. backend: Optional, the backend to characterize. Raises: QiskitError: If args are not valid. """ if physical_qubits is None: if backend is None: raise QiskitError("`physical_qubits` and `backend` kwargs cannot both be None.") num_qubits = 0 if isinstance(backend, BackendV2): num_qubits = backend.target.num_qubits elif isinstance(backend, Backend): num_qubits = backend.configuration().num_qubits if num_qubits: physical_qubits = range(num_qubits) else: raise QiskitError(f"Cannot infer backend qubits from backend {backend}") super().__init__(physical_qubits, backend=backend) self.analysis = LocalReadoutErrorAnalysis()
[docs] def circuits(self) -> List[QuantumCircuit]: """Returns the experiment's circuits""" labels = ["0" * self.num_qubits, "1" * self.num_qubits] return [calibration_circuit(self.num_qubits, label) for label in labels]