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QFI

class QFI(qfi_method='lin_comb_full')

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Bases: qiskit.opflow.gradients.qfi_base.QFIBase

Compute the Quantum Fisher Information (QFI).

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

QFIkl=4Re[kψlψkψψψlψ].\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].

Parameters

qfi_method (Union[str, CircuitQFI]) – The method used to compute the state/probability gradient. Can be either a CircuitQFI instance or one of the following pre-defined strings 'lin_comb_full', 'overlap_diag'` or 'overlap_block_diag'`.

Raises

ValueError – if qfi_method is neither a CircuitQFI object nor one of the predefined strings.


Methods Defined Here

convert

QFI.convert(operator, params=None)

Parameters

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

Return type

ListOp

Returns

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

Raises

ValueError – If operator is not parameterized.


Attributes

qfi_method

Returns CircuitQFI.

Return type

CircuitQFI

Returns

CircuitQFI.

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