Optimal series representations for numerical path integral simulations

By means of the Ito-Nisio theorem, we introduce and discuss a general approach to series representations of path integrals. We then argue that the optimal basis for both ``primitive'' and partial averaged approaches is the Wiener sine-Fourier basis. The present analysis also suggests a new approach to improving the convergence of primitive path integral methods. Current work indicates that this new technique, the ``reweighted'' method, converges as the cube of the number of path variables for ``smooth'' potentials. The technique is based on a special way of approximating the Brownian bridge which enters the Feynman-Kac formula and it does not require the Gaussian transform of the potential for its implementation.