  We present a numerical investigation of the thermal and structural properties
of the $^3$He-He II sandwich system adsorbed on a graphite substrate using the
Worm Algorithm Quantum Monte Carlo (WAQMC) method (Boninsegni et al., Phys.
Rev. E 74, 036701 (2006)). For this purpose, we modified a previously written
WAQMC code originally adapted for $^4$He on graphite, by including the second
$^3$He-component. In order to describe the fermions, a temperature-dependent
statistical potential was used which proved very effective. To the best of our
knowledge, the statistical potential has not been used before in Quantum Monte
Carlo techniques for describing fermions. In an unprecedented task, the WAQMC
calculations were conducted in the milli-Kelvin temperature regime. However,
because of the heavy computations involved, only 30, 40, and 50 mK were
considered for the time being. The pair correlations, Matsubara Green's
function, structure factor, and density profiles were explored at theses
temperatures. (Note: this paper is just a preliminary version and will be
replaced by an updated version.
