Worm algorithm for continuous-space Path Integral Monte Carlo simulations

We present a new approach to Path Integral Monte Carlo (PIMC) simulations based on the ``worm" algorithm, originally developed for lattice models,\footnote{N. V. Prokof'ev, B. V. Svistunov, and I. S. Tupitsyn, Phys. Lett. {\bf 238}, 253 (1998)} and recently extended to continuous-space many-body systems.\footnote{M. Boninsegni, N. Prokof'ev and B. Svistunov, cond-mat/0510214} The scheme allows for efficient computation of thermodynamic properties, including winding numbers and off-diagonal correlations, for systems of much greater size than that accessible to conventional PIMC. We present results for the superfluid transition of Helium-four in two and three dimensions. Using systems comprising several thousand particles, a very accurate determination of the superfluid transition temperature is feasible.