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qiskit.opflow.gradients.QFIBase(qfi_method='lin_comb_full') GitHub(opens in a new tab)

Bases: DerivativeBase

Deprecated: Base class for Quantum Fisher Information (QFI).

Compute the Quantum Fisher Information (QFI) given a pure, parameterized quantum state.

The QFI is:

[QFI]kl= Re[〈∂kψ|∂lψ〉−〈∂kψ|ψ〉〈ψ|∂lψ〉] * 4.

Deprecated since version 0.24.0

The class qiskit.opflow.gradients.qfi_base.QFIBase is deprecated as of qiskit-terra 0.24.0. It will be removed in the Qiskit 1.0 release. For code migration guidelines, visit in a new tab).


qfi_method (str(opens in a new tab) |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'`.


ValueError(opens in a new tab) – if qfi_method is neither a CircuitQFI object nor one of the predefined strings.



Returns CircuitQFI.



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