ROLE OF WINDING NUMBERS IN QUANTUM MONTE-CARLO SIMULATIONS

We discuss the effects of fixing the winding number in quantum Monte C arlo simulations. We present a simple geometrical argument as well as strong numerical evidence that one can obtain exact ground stale resul ts fur periodic boundary conditions without changing the winding numbe r. However, for very small systems the temperature has to be considera bly lower than in simulations with fluctuating winding numbers. The re lative deviation of a calculated observable from the exact ground stat e result typically scales as TY, where the exponent gamma is model and observable dependent and the prefactor decreases with increasing syst em size. Analytic results for a quantum rotor model further support ou r claim.