The PVLAS experiment: a 25 year effort to measure vacuum magnetic birefringence

TL;DR

The PVLAS experiment, after 25 years, set the most stringent limits on vacuum magnetic birefringence and dichroism, although it did not reach the predicted QED values, using rotating magnets to probe quantum vacuum properties.

Contribution

This work provides the first comprehensive long-term measurement of vacuum magnetic birefringence with improved limits, employing two different magnet configurations over 25 years.

Findings

Set the current best experimental limits on vacuum birefringence and dichroism.

Did not observe the predicted QED vacuum birefringence value.

Demonstrated the feasibility of long-term precision measurements of quantum vacuum effects.

Abstract

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.