Note

This is the documentation for the current state of the development branch of Qiskit Experiments. The documentation or APIs here can change prior to being released.

LocalReadoutError

class LocalReadoutError(physical_qubits=None, backend=None)

An experiment for characterizing local readout error.

Overview

This class constructs a LocalReadoutMitigator containing a sequence of assignment matrices $A$ characterizing the readout error for the given qubits from the experiment results. The full assignment matrix is accessible via the 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 $2^n\times 2^n$ matrix $A$ such that $A_{y,x}$ is the probability to observe $y$ given the true outcome should be $x$. 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 $n$ $2\times 2$ matrices, one for each qubit, making it practical to store the assignment matrix in implicit form, by storing the individual $2\times 2$ assignment matrices. The corresponding class in Qiskit is the LocalReadoutMitigator in qiskit.result.

The experiment generates 2 circuits, corresponding to the states $|0^n⟩$ and $|1^n⟩$, measuring the error in all the qubits at once, and constructs the assignment matrix and local mitigator from the results.

See LocalReadoutErrorAnalysis documentation for additional information on local readout error experiment analysis.

References

[1] Sergey Bravyi, Sarah Sheldon, Abhinav Kandala, David C. Mckay, Jay M. Gambetta, Mitigating measurement errors in multi-qubit experiments, Phys. Rev. A 103, 042605 (2021), doi: 10.1103/PhysRevA.103.042605 (open)

Analysis class reference

LocalReadoutErrorAnalysis

Experiment options

These options can be set by the set_experiment_options() method.

Options

• Defined in the class BaseExperiment:

  • max_circuits (Optional[int])

    Default value: None

    The maximum number of circuits per job when running an experiment on a backend.

Initialization

Initialize a local readout error characterization experiment.

Parameters:

• physical_qubits (Optional[Iterable[int]]) – Optional, the backend qubits being characterized for readout error. If None all qubits on the provided backend will be characterized.

• backend (Optional[Backend]) – Optional, the backend to characterize.

Raises:

QiskitError – If args are not valid.

Attributes

LocalReadoutError.analysis	Return the analysis instance for the experiment
LocalReadoutError.backend	Return the backend for the experiment
LocalReadoutError.experiment_options	Return the options for the experiment.
LocalReadoutError.experiment_type	Return experiment type.
LocalReadoutError.num_qubits	Return the number of qubits for the experiment.
LocalReadoutError.physical_qubits	Return the device qubits for the experiment.
LocalReadoutError.run_options	Return options values for the experiment run() method.
LocalReadoutError.transpile_options	Return the transpiler options for the run() method.

Methods

LocalReadoutError.circuits()	Returns the experiment's circuits
LocalReadoutError.config()	Return the config dataclass for this experiment
LocalReadoutError.copy()	Return a copy of the experiment
LocalReadoutError.from_config(config)	Initialize an experiment from experiment config
LocalReadoutError.run([backend, analysis, ...])	Run an experiment and perform analysis.
LocalReadoutError.set_experiment_options(...)	Set the experiment options.
LocalReadoutError.set_run_options(**fields)	Set options values for the experiment run() method.
LocalReadoutError.set_transpile_options(**fields)	Set the transpiler options for run() method.