qiskit/releasenotes/notes/0.22/add-reverse-linear-entangle...

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---
features:
- |
Added a new supported value, ``"reverse_linear"`` for the ``entanglement`` keyword argument
to the constructor for the :class:`~.NLocal` circuit class. For :class:`~.TwoLocal` circuits
(which are subclassess of :class:`~.NLocal`), if ``entanglement_blocks="cx"`` then
using ``entanglement="reverse_linear"`` provides an equivalent n-qubit circuit as
``entanglement="full"`` but with only :math:`n-1` :class:`~.CXGate` gates, instead of
:math:`\frac{n(n-1)}{2}`.
upgrade:
- |
The default value for the ``entanglement`` keyword argument on the constructor for the
:class:`~.RealAmplitudes` and :class:`~.EfficientSU2` classes has changed from ``"full"`` to
``"reverse_linear"``. This change was made because the output circuit is equivalent but
uses only :math:`n-1` instead of :math:`\frac{n(n-1)}{2}` :class:`~.CXGate` gates. If you
desire the previous default you can explicitly set ``entanglement="full"`` when calling either
constructor.