Exact Quantum Monte Carlo Process for the Statistics of Discrete Systems
  We introduce an exact Monte Carlo approach to the statistics of discrete quantum systems which does not rely on the standard fragmentation of the imaginary time, or any small parameter. The method deals with discrete objects, kinks, representing virtual transitions at different moments of time. The global statistics of kinks is reproduced by explicit local procedures, the key one being based on the exact solution for the biased two-level system. 
N.V. Prokof'ev, B.V. Svistunov, and I.S. Tupitsyn