qiskit/releasenotes/notes/0.23/add-qfi-with-primitive-86d9...

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---
features:
- |
New Quantum Fisher Information (QFI) and Quantum Geometric Tensor (QGT) algorithms using the
primitives, :class:`qiskit.algorithms.gradients.QFI` and
:class:`qiskit.algorithms.gradients.LinCombQGT`, have been added to the gradients module.
Example::
.. code-block:: python
from qiskit.circuit import QuantumCircuit, Parameter
from qiskit.algorithms.gradients import LinCombQGT, QFI
estimator = Estimator()
a, b = Parameter("a"), Parameter("b")
qc = QuantumCircuit(1)
qc.h(0)
qc.rz(a, 0)
qc.rx(b, 0)
parameter_value = [[np.pi / 4, 0]]
qgt = LinCombQGT(estimator)
qgt_result = qgt.run([qc], parameter_value).result()
qfi = QFI(qgt)
qfi_result = qfi.run([qc], parameter_value).result()
- |
We can now specify the derivative type of
:class:`qiskit.algorithms.gradients.LinCombEstimatorGradient` and can compute the imaginary parts
of the gradients additional to the real part.