T2Hahn

class T2Hahn(physical_qubits, delays, num_echoes=1, backend=None)[source]

An experiment to measure the dephasing time insensitive to inhomogeneous broadening using Hahn echos.

Overview

This experiment is used to estimate the \(T_2\) time of a single qubit. \(T_2\) is the dephasing time or the transverse relaxation time of the qubit on the Bloch sphere as a result of both energy relaxation and pure dephasing in the transverse plane. Unlike \(T_2^*\), which is measured by T2Ramsey, \(T_2\) is insensitive to inhomogenous broadening.

This experiment consists of a series of circuits of the form

     ┌─────────┐┌──────────┐┌───────┐┌──────────┐┌─────────┐┌─┐
q_0: ┤ Rx(π/2) ├┤ DELAY(t) ├┤ RX(π) ├┤ DELAY(t) ├┤ RX(π/2) ├┤M├
     └─────────┘└──────────┘└───────┘└──────────┘└─────────┘└╥┘
c: 1/════════════════════════════════════════════════════════╩═
                                                             0

for each t from the specified delay times and the delays are specified by the user. The delays that are specified are delay for each delay gate while the delay in the metadata is the total delay which is delay * (num_echoes +1) The circuits are run on the device or on a simulator backend.

References

[1] Philip Krantz, Morten Kjaergaard, Fei Yan, Terry P. Orlando, Simon Gustavsson, William D. Oliver, A Quantum Engineer’s Guide to Superconducting Qubits, Applied Physics Reviews 6, 021318 (2019), doi: 10.1063/1.5089550 (open)

User manual

T2 Hahn Characterization

Analysis class reference

T2HahnAnalysis

Experiment options

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

Options

  • Defined in the class T2Hahn:

    • delays (Iterable[float])

      Default value: None
      Delay times of the experiments.

    • num_echoes (int)

      Default value: 1
      The number of echoes to preform.

  • 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.

Example

import numpy as np
from qiskit_experiments.library.characterization.t2hahn import T2Hahn

delays = np.linspace(0, 50, 51)*1e-6

exp = T2Hahn(physical_qubits=(0, ),
             delays=delays,
             backend=backend)
exp.analysis.set_options(p0=None, plot=True)

exp_data = exp.run().block_for_results()
display(exp_data.figure(0))
exp_data.analysis_results(dataframe=True)
../_images/qiskit_experiments.library.characterization.T2Hahn_1_0.png
name experiment components value quality backend run_time chisq unit
a480e1f0 @Parameters_T2HahnAnalysis T2Hahn [Q0] CurveFitResult:\n - fitting method: least_squa... good T2Hahn_simulator None None None
5a57d198 T2 T2Hahn [Q0] (1.96+/-0.10)e-05 good T2Hahn_simulator None 1.002813 s

Initialization

Initialize the T2 - Hahn Echo class.

Parameters:

  • physical_qubits (Sequence[int]) – a single-element sequence containing the qubit whose T2 is to be estimated.

  • delays (List[float] | array) – Total delay times of the experiments.

  • backend (Backend | None) – Optional, the backend to run the experiment on.

  • num_echoes (int) – The number of echoes to preform.

  • backend – Optional, the backend to run the experiment on.

Raises:

QiskitError – Error for invalid input.

Attributes

analysis

Return the analysis instance for the experiment

backend

Return the backend for the experiment

experiment_options

Return the options for the experiment.

experiment_type

Return experiment type.

num_qubits

Return the number of qubits for the experiment.

physical_qubits

Return the device qubits for the experiment.

run_options

Return options values for the experiment run() method.

transpile_options

Return the transpiler options for the run() method.

Methods

circuits()[source]

Return a list of experiment circuits.

Each circuit consists of RX(π/2) followed by a sequence of delay gate, RX(π) for echo and delay gate again. The sequence repeats for the number of echoes and terminates with RX(±π/2).

Returns:

The experiment circuits.

Return type:

List[QuantumCircuit]

config()

Return the config dataclass for this experiment

Return type:

ExperimentConfig

copy()

Return a copy of the experiment

Return type:

BaseExperiment

classmethod from_config(config)

Initialize an experiment from experiment config

Return type:

BaseExperiment

job_info(backend=None)

Get information about job distribution for the experiment on a specific backend.

Parameters:

backend (Backend) – Optional, the backend for which to get job distribution information. If not specified, the experiment must already have a set backend.

Returns:

A dictionary containing information about job distribution.

  • ”Total number of circuits in the experiment”: Total number of circuits in the experiment.

  • ”Maximum number of circuits per job”: Maximum number of circuits in one job based on backend and experiment settings.

  • ”Total number of jobs”: Number of jobs needed to run this experiment on the currently set backend.

Return type:

dict

Raises:

QiskitError – if backend is not specified.

run(backend=None, sampler=None, analysis='default', timeout=None, backend_run=None, **run_options)

Run an experiment and perform analysis.

Parameters:

  • backend (Backend | None) – Optional, the backend to run on. Will override existing backend settings.

  • sampler (BaseSamplerV2 | None) – Optional, the sampler to run the experiment on. If None then a sampler will be invoked from previously set backend

  • analysis (BaseAnalysis | None) – Optional, a custom analysis instance to use for performing analysis. If None analysis will not be run. If "default" the experiments analysis() instance will be used if it contains one.

  • timeout (float | None) – Time to wait for experiment jobs to finish running before cancelling.

  • backend_run (bool | None) – Use backend run (temp option for testing)

  • run_options – backend runtime options used for circuit execution.

Returns:

The experiment data object.

Raises:

QiskitError – If experiment is run with an incompatible existing ExperimentData container.

Return type:

ExperimentData

set_experiment_options(**fields)

Set the experiment options.

Parameters:

fields – The fields to update the options

Raises:

AttributeError – If the field passed in is not a supported options

set_run_options(**fields)

Set options values for the experiment run() method.

Parameters:

fields – The fields to update the options

See also

The Setting options for your experiment guide for code example.

set_transpile_options(**fields)

Set the transpiler options for run() method.

Parameters:

fields – The fields to update the options

Raises:

QiskitError – If initial_layout is one of the fields.

See also

The Setting options for your experiment guide for code example.