A calculation of quantities of interest requires summing over all possible string configurations for all the particles. This formidably large phase space is explored efficiently by using Monte Carlo techniques. As the quantum phase transition is approached by increasing the disorder strength, the correlation length and correlation time, which describe the range over which fluctuations exist, become very large and ultimately diverge at the transition. Therefore, in order to reliably study such phenomena, it is important to have data on large lattices and to perform a careful finite-size scaling analysis. This is achieved by distributing regions of the lattice among the nodes of a concurrent processor.
Trotter slices is packed in one word.
All the moves are implemented through bit-wise logical operations on words. Another feature of disorder-related problems is that it is necessary to average over several disorder configurations. The parallel computer is ideally suited for such purposes. Thus, on a 512-node Delta, if we had the whole machine, we could run 32 independent realizations of disorder simultaneously. The results obtained from the simulations have provided important insights into the phase diagram.