If the fermion mass is large enough, the phase of the fermion determinant of QCD at finite density is strongly correlated with the imaginary part of the Polyakov loop. This fact can be exploited to reduce the fluctuations of the phase significantly, making numerical simulations feasible in regions of parameters where the naive brute force method does not work.
@article{arxiv.hep-lat/9908015,
title = {Improving the sign problem in QCD at finite density},
author = {Philippe de Forcrand and Victor Laliena},
journal= {arXiv preprint arXiv:hep-lat/9908015},
year = {2015}
}