QFI

class qiskit.opflow.gradients.QFI(qfi_method='lin_comb_full')

Bases: QFIBase

Deprecated: Compute the Quantum Fisher Information (QFI).

Computes the QFI given a pure, parameterized quantum state, where QFI is:

\[\mathrm{QFI}_{kl}= 4 \mathrm{Re}[\langle \partial_k \psi | \partial_l \psi \rangle − \langle\partial_k \psi | \psi \rangle \langle\psi | \partial_l \psi \rangle].\]

Deprecated since version 0.24.0: The class qiskit.opflow.gradients.qfi.QFI is deprecated as of qiskit-terra 0.24.0. It will be removed no earlier than 3 months after the release date. For code migration guidelines, visit https://qisk.it/opflow_migration.

Attributes

qfi_method

Returns CircuitQFI.

Returns:

CircuitQFI.

Methods

convert(operator, params=None)

Parameters:

• operator (CircuitStateFn) – The operator corresponding to the quantum state |ψ(ω)〉for which we compute the QFI

• params (ParameterVector | ParameterExpression | List[ParameterExpression] | None) – The parameters we are computing the QFI wrt: ω If not explicitly passed, they are inferred from the operator and sorted by name.

Returns:

ListOp[ListOp] where the operator at position k,l corresponds to QFI_kl

Raises:

ValueError – If operator is not parameterized.

Return type:

ListOp