cirq.xeb_fidelity

Estimates XEB fidelity from one circuit using user-supplied estimator.

cirq.xeb_fidelity(
    circuit: cirq.Circuit,
    bitstrings: Sequence[int],
    qubit_order: cirq.QubitOrderOrList = cirq.QubitOrder.DEFAULT,
    amplitudes: Optional[Mapping[int, complex]] = None,
    estimator: Callable[[int, Sequence[float]], float] = cirq.linear_xeb_fidelity_from_probabilities
) -> float

Fidelity quantifies the similarity of two quantum states. Here, we estimate the fidelity between the theoretically predicted output state of circuit and the state produced in its experimental realization. Note that we don't know the latter state. Nevertheless, we can estimate the fidelity between the two states from the knowledge of the bitstrings observed in the experiment.

In order to make the estimate more robust one should average the estimates over many random circuits. The API supports per-circuit fidelity estimation to enable users to examine the properties of estimate distribution over many circuits.

See https://arxiv.org/abs/1608.00263 for more details.

circuit Random quantum circuit which has been executed on quantum processor under test.
bitstrings Results of terminal all-qubit measurements performed after each circuit execution as integer array where each integer is formed from measured qubit values according to qubit_order from most to least significant qubit, i.e. in the order consistent with cirq.final_state_vector.
qubit_order Qubit order used to construct bitstrings enumerating qubits starting with the most significant qubit.
amplitudes Optional mapping from bitstring to output amplitude. If provided, simulation is skipped. Useful for large circuits when an offline simulation had already been performed.
estimator Fidelity estimator to use, see above. Defaults to the linear XEB fidelity estimator.

Estimate of fidelity associated with an experimental realization of circuit which yielded measurements in bitstrings.

ValueError Circuit is inconsistent with qubit order or one of the bitstrings is inconsistent with the number of qubits.