qiskit.ignis.characterization.T2StarFitter

class T2StarFitter(backend_result, xdata, qubits, fit_p0, fit_bounds, time_unit='micro-seconds')

Estimate T₂^*, based on experiments outcomes.

The experiments were created by t2star_circuits, and executed on the device.

The probabilities of measuring 0 is assumed to be of the form

\[f(t) = A\mathrm{e}^{-t / T_2^*}\cos(2\pi ft + \phi) + B\]

for unknown parameters \(A, B, f, \phi, T_2^*\).

Parameters

• backend_result (Result) – result of execution of t2star_circuits on the backend.

• xdata (Union[List[float], array]) – delay times of the T₂^* circuits.

• qubits (List[int]) – indices of the qubits whose T₂:sup:* ‘s are to be measured.

• fit_p0 (List[float]) – initial values to the fit parameters, where the order is \((A, T_2^*, f, \phi, B)\).

• fit_bounds (Tuple[List[float], List[float]]) – bounds on the parameters to fit. The first tuple is the lower bounds, in the order \((A, T_2^*, f, \phi, B)\). The second tuple is the upper bounds.

• time_unit (str) – unit of delay times in xdata.

__init__(backend_result, xdata, qubits, fit_p0, fit_bounds, time_unit='micro-seconds')

Initialize self. See help(type(self)) for accurate signature.

Methods

__init__(backend_result, xdata, qubits, …)	Initialize self.
add_data(results[, recalc, refit])	Add new execution results to previous execution results
fit_data([qid, p0, bounds, series])	Fit the curve.
guess_params([qind])	Guess fit parameters for oscillation data
plot(qind[, series, ax, show_plot])	Plot coherence data.
time([qid, series])	Return the characteristic time for the given qubit and series
time_err([qid, series])	Return the error of characteristic time for the given qubit and series

Attributes

backend_result	Return the execution results
description	Return the fitter’s purpose, e.g.
fit_fun	Return the function used in the fit, e.g.
measured_qubits	Return the indices of the qubits to be characterized
params	Return the fit function parameters that were calculated by curve_fit
params_err	Return the error of the fit function parameters
series	Return the list of series for the data
xdata	Return the data points on the x-axis, the independenet parameter which is fit against
ydata	Return the data points on the y-axis

add_data(results, recalc=True, refit=True)

Add new execution results to previous execution results

Parameters

• results (Union[Result, List[Result]]) – new execution results

• recalc (bool) – whether tp recalculate the data

• refit (bool) – whether to refit the data

property backend_result

Return the execution results

Return type

Union[Result, List[Result]]

property description

Return the fitter’s purpose, e.g. ‘T1’

Return type

str

fit_data(qid=- 1, p0=None, bounds=None, series=None)

Fit the curve.

Compute self._params and self._params_err

Parameters

• qid (int) – qubit for fitting. If -1 fit for all the qubits

• p0 (Optional[List[float]]) – initial guess, equivalent to p0 in scipy.optimize

• bounds (Optional[Tuple[List[float], List[float]]]) – bounds, equivalent to bounds in scipy.optimize

• series (Optional[str]) – series to fit (if None fit all)

property fit_fun

Return the function used in the fit, e.g. BaseFitter._exp_fit_fun

Return type

Callable

guess_params(qind=0)

Guess fit parameters for oscillation data

Parameters

qind (int) – qubit index to guess fit parameters for

Return type

List[float]

Returns

Fit guessed parameters

property measured_qubits

Return the indices of the qubits to be characterized

Return type

List[int]

property params

Return the fit function parameters that were calculated by curve_fit

Return type

List[float]

property params_err

Return the error of the fit function parameters

Return type

List[float]

plot(qind, series='0', ax=None, show_plot=False)

Plot coherence data.

Parameters

• qind – qubit index to plot

• series – which series to plot (if list then plot multiple)

• ax – plot axes

• show_plot – whether to call plt.show()

Returns

The axes object

Return type

Axes

Raises

ImportError – if matplotlib is not installed

property series

Return the list of series for the data

Return type

Optional[List[str]]

time(qid=- 1, series='0')

Return the characteristic time for the given qubit and series

Parameters

• qid (int) – the qubit index (or all qubits if -1)

• series (str) – the series to get

Return type

Union[float, List[float]]

Returns

The characteristic time of the qubit, or all qubits

time_err(qid=- 1, series='0')

Return the error of characteristic time for the given qubit and series

Parameters

• qid (int) – the qubit index (or all qubits if -1)

• series (str) – the series to get

Return type

Union[float, List[float]]

Returns

The error of the characteristic time of the qubit, or all qubits

property xdata

Return the data points on the x-axis, the independenet parameter which is fit against

Return type

Union[List[float], array]

property ydata

Return the data points on the y-axis

The data points are returning in the form of a list of dictionaries:

• ydata[i][‘mean’] is a list, where item

  no. j is the probability of success of qubit i for a circuit that lasts xdata[j].

• ydata[i][‘std’] is a list, where ydata[‘std’][j] is the

  standard deviation of the success of qubit i.

Return type

List[Dict]