T2StarFitter

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.

Attributes

backend_result

Union[qiskit.result.result.Result, List[qiskit.result.result.Result]]

Return the execution results

Return type

Union[Result, List[Result]]

description

str

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

Return type

str

fit_fun

Callable

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

Return type

Callable

measured_qubits

List[int]

Return the indices of the qubits to be characterized

Return type

List[int]

params

List[float]

Return the fit function parameters that were calculated by curve_fit

Return type

List[float]

params_err

List[float]

Return the error of the fit function parameters

Return type

List[float]

series

Optional[List[str]]

Return the list of series for the data

Return type

Optional[List[str]]

xdata

Union[List[float], numpy.array]

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

Return type

Union[List[float], array]

ydata

List[Dict]

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]

Methods

add_data

T2StarFitter.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

fit_data

T2StarFitter.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)

guess_params

T2StarFitter.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

plot

T2StarFitter.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

time

T2StarFitter.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

T2StarFitter.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

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