qiskit/releasenotes/notes/0.16/linear-amplitude-function-8...

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A new class :class:`~qiskit.circuit.library.LinearAmplitudeFunction` was
added to the circuit library (:mod:`qiskit.circuit.library`) for mapping
(piecewise) linear functions on qubit amplitudes,
.. math::
F|x\rangle |0\rangle = \sqrt{1 - f(x)}|x\rangle |0\rangle + \sqrt{f(x)}|x\rangle |1\rangle
The mapping is based on a controlled Pauli Y-rotations and
a Taylor approximation, as described in https://arxiv.org/abs/1806.06893.
This circuit can be used to compute expectation values of linear
functions using the quantum amplitude estimation algorithm.