LIGO Subtlety

I simply can't get over the beautiful simplicity of the experiment that discovered gravity waves. The shift in the length of the beams was miniscule. Look (New York Times):

This difference is so small that even the minuscule motion in the position of each mirror at the end of each tunnel because of quantum mechanical vibrations of the atoms in the mirror could have overwhelmed the signal. But scientists were able to resort to the most modern techniques in quantum optics to overcome this.