Compute grid parallel two-qubit XEB results from experimental data.

XEB fidelities are calculated using the least squares XEB fidelity estimator with the linear cross entropy observable. Using notation from the docstring of cirq.experiments.least_squares_xeb_fidelity_from_expectations, the linear cross entropy observable O_U has eigenvalue corresponding to the computational basis state |z⟩ given by D * |⟨z|𝜓_U⟩|^2.

Purity values are calculated using speckle purity benchmarking. For details, see the docstring of the method cirq.experiments.purity_from_probabilities.

Results are saved in the file {base_dir}/{data_collection_id}/results.json.

data_collection_id The data collection ID of the data set to analyze.
num_processors The number of CPUs to use.
base_dir The base directory from which to read data.

CrossEntropyResultDict mapping qubit pairs to XEB results.

Side effects:

Saves the returned CrossEntropyResultDict to the file {base_dir}/{data_collection_id}/results.json.