qiskit/releasenotes/notes/0.21/swap-strategies-3ab013ca60f...

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New transpiler passes have been added. The transpiler pass :class:`.Commuting2qGateRouter`
uses swap strategies to route a block of commuting gates to the coupling map. Indeed, routing
is a hard problem but is significantly easier when the gates commute as in CZ networks.
Blocks of commuting gates are also typically found in QAOA. Such cases can be dealt with
using swap strategies that apply a predefined set of layers of SWAP gates. Furthermore, the new
transpiler pass :class:`.FindCommutingPauliEvolutions` identifies blocks of Pauli evolutions
made of commuting two-qubit terms. Here, a swap strategy is specified by the class
:class:`.SwapStrategy`. Swap strategies need to be tailored to the coupling map and, ideally,
the circuit for the best results.