cirq.xeb_fidelity¶

cirq.xeb_fidelity(circuit: cirq.circuits.circuit.Circuit, bitstrings: Sequence[int], qubit_order: Union[cirq.ops.qubit_order.QubitOrder, Iterable[cirq.ops.raw_types.Qid]] = <cirq.ops.qubit_order.QubitOrder object>, amplitudes: Optional[Mapping[int, complex]] = None, estimator: Callable[[int, Sequence[float]], float] = <function linear_xeb_fidelity_from_probabilities>) → float[source]

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

Fidelity quantifies the similarity of two quantum states. Here, we estimate
the fidelity between the theoretically predicted output state of circuit and
the state producted 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.

Parameters
• 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_wavefunction.

• qubit_order – Qubit order used to construct bitstrings enumerating qubits starting with the most sigificant 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 peformed.

• estimator – Fidelity estimator to use, see above. Defaults to the linear XEB fidelity estimator.

Returns

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

Raises

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