Blockspin Scheme and Cluster Algorithm for Quantum Spin Systems
  We present a numerical study using a cluster algorithm for the 1-d $S=1/2$ quantum Heisenberg models. The dynamical critical exponent for anti-ferromagnetic chains is $z=0.0(1)$ such that critical slowing down is eliminated. 
He-Ping Ying and Uwe-Jens Wiese (Bern University)