  We report on coulomb explosion imaging of the wavefunction of the quantum
halo system He$_2$. Each atom of this system is ionized by tunnelionization in
a femto second laser pulse and in a second experiment by single photon
ionization employing a free electron laser. We visualize the exponential decay
of the probability density of the tunneling particle over distance for over two
orders of magnitude up to an internuclear distance of 250 {\AA}. By fitting the
slope of the density in the tunneling regime we obtain a binding energy of
151.9 $\pm$ 13.3 neV, which is in agreement with most recent calculations.
