# QFI¶

class QFI(qfi_method='lin_comb_full')[source]

Compute the Quantum Fisher Information (QFI).

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

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

Attributes

qfi_method

Returns CircuitQFI.

Return type

CircuitQFI

Returns

CircuitQFI.