  Taking the gauge invariant quark correlator as an example, in this work we
perform a direct comparison of lattice QCD simulations with the QCD sum rule
approach. The quark correlator is first investigated in the framework of QCD
sum rules and the correlation length of the quark field is calculated.
Comparing the phenomenological part of the sum rule with previous measurements
of the quark correlator on the lattice, we are able to obtain an independent
result for the correlation length. From a fit of the lattice data to the
operator product expansion, the quark condensate and the mixed quark-gluon
condensate can be extracted.
