qiskit.algorithms.optimizers.QNSPSA.get_fidelity¶

static QNSPSA.get_fidelity(circuit, backend=None, expectation=None, *, sampler=None)[source]¶

Get a function to compute the fidelity of circuit with itself.

Note

Using this function with a backend and expectation converter is pending deprecation, instead pass a Qiskit Primitive sampler, such as Sampler. The sampler can be passed as keyword argument or, positionally, as second argument.

Let circuit be a parameterized quantum circuit performing the operation \(U(\theta)\) given a set of parameters \(\theta\). Then this method returns a function to evaluate

\[F(\theta, \phi) = \big|\langle 0 | U^\dagger(\theta) U(\phi) |0\rangle \big|^2.\]

The output of this function can be used as input for the fidelity to the QNSPSA optimizer.

Deprecated since version 0.24.0: qiskit.algorithms.optimizers.qnspsa.QNSPSA.get_fidelity()’s argument expectation is deprecated as of qiskit-terra 0.24.0. It will be removed no earlier than 3 months after the release date. See https://qisk.it/algo_migration for a migration guide.

Deprecated since version 0.24.0: qiskit.algorithms.optimizers.qnspsa.QNSPSA.get_fidelity()’s argument backend is deprecated as of qiskit-terra 0.24.0. It will be removed no earlier than 3 months after the release date. See https://qisk.it/algo_migration for a migration guide.

Parameters

circuit (QuantumCircuit) – The circuit preparing the parameterized ansatz.
backend (Backend | QuantumInstance | None) – Deprecated. A backend of quantum instance to evaluate the circuits. If None, plain matrix multiplication will be used.
expectation (ExpectationBase | None) – Deprecated. An expectation converter to specify how the expected value is computed. If a shot-based readout is used this should be set to PauliExpectation.
sampler (BaseSampler | None) – A sampler primitive to sample from a quantum state.

Returns

A handle to the function \(F\).

Return type

Callable[[np.ndarray, np.ndarray], float]