mtreinish/vf2_partial_layout

An experimental Layout Pass for Qiskit's compiler

VF2 Partial Layout Plugin

This repo contains an experimental transpiler pass VF2PartialLayout which is for performing the layout stage of compilation (ie initial qubit selection). This pass leverages the vf2 implementation in rustworkx to find a layout using subgraph isomorphsim of a partial interaction graph and the coupling map. Unlike VF2Layout (and VF2PostLayout) it gives up on finding a perfect layout for the full interaction graph and instead builds partial interaction graphs over the circuit and tries to find the most complete interaction graph that has a matching subgraph. The best performing qubits are then matched for this subgraph (per the normal vf2 layout algorithm) and that is used as the core of the initial layout.

Installing

Right now the package is not published on pypi but you can install it with pip still by running:

pip install git+https://github.com/mtreinish/vf2_partial_layout

Usage

Once you have it installed you can use the VF2PartialLayout method by specifying layout_method="vf2_partial" when calling transpile. For example:

from qiskit.circuit.library import QFT
from qiskit import transpile
from qiskit.providers.fake_provider import FakeAuckland
qc = QFT(4)
qc.measure_all()

tqc = transpile(qc, FakeAuckland(), layout_method='vf2_partial')

Note this pass is still experimental and also known to be quite memory hungry in its current form. The eventual goal is to have this pass as part of qiskit-terra after we prove it's effectiveness and decrease the memory overhead.