Suppression of the negative sign problem in quantum Monte Carlo
  We present a new Monte Carlo algorithm for simulating quantum spin systems which is able to suppress the negative sign problem. This algorithm has only a linear complexity in the lattice size used for the simulation. A general description and a rigorous proof of its correctness is given. Its efficiency is tested on a simple 2-dimensional fermionic model. For this model we show that our algorithm eliminates the sign problem. 
A. Galli (Max-Planck-Institut fuer Physik)