  We present thermodynamic measurements of various physical observables of the
two dimensional S=1/2 isotropic quantum Heisenberg antiferromagnet on a square
lattice, obtained by quantum Monte Carlo. In particular we have been able to
measure the infinite volume limit of the uniform susceptibility up to the
inverse temperature beta=40, the analysis of which reveals the correct
asymptotic behavior in excellent agreement with the prediction of chiral
perturbation theory. The controversy over the existence of a crossover from
quantum critical to renormalized classical regime is resolved.
