  This paper describes the 25 year effort to measure vacuum magnetic
birefringence and dichroism with the PVLAS experiment. The experiment went
through two main phases: the first using a rotating superconducting magnet and
the second using two rotating permanent magnets. The experiment was not able to
reach the predicted value from QED. Nonetheless the experiment set the current
best limits on vacuum magnetic birefringence and dichroism for a field of
$B_{\rm ext} = 2.5$ T, namely, $\Delta n^{\rm (PVLAS)} =
(12\pm17)\times10^{-23}$ and $|\Delta\kappa|^{\rm (PVLAS)} =
(10\pm28)\times10^{-23}$. The uncertainty on $\Delta n^{\rm (PVLAS)}$ is about
a factor 7 above the predicted value of $\Delta n^{\rm (QED)} =
2.5\times10^{-23}$ @ 2.5 T.

Optics;High Energy Physics - Experiment