Measuring the magnetic birefringence of vacuum: the PVLAS experiment

TL;DR

The PVLAS experiment aims to detect vacuum magnetic birefringence predicted by QED, using a high finesse optical cavity and rotating magnets, also probing for new physics like axion-like particles.

Contribution

This work reports the construction of the PVLAS apparatus and improved limits on non-linear electrodynamic effects in vacuum through initial measurements.

Findings

Improved the limit on the parameter $A_e$ by a factor of 2.

Constructed a high finesse Fabry-Perot cavity with $>2\times10^5$ finesse.

Performed initial measurements with a scaled test setup.

Abstract

We describe the principle and the status of the PVLAS experiment which is presently running at the INFN section of Ferrara, Italy, to detect the magnetic birefringence of vacuum. This is related to the QED vacuum structure and can be detected by measuring the ellipticity acquired by a linearly polarized light beam propagating through a strong magnetic field. Such an effect is predicted by the Euler-Heisenberg Lagrangian. The method is also sensitive to other hypothetical physical effects such as axion-like particles and in general to any fermion/boson millicharged particle. Here we report on the construction of our apparatus based on a high finesse ($>2\cdot10^5$) Fabry-Perot cavity and two 0.9 m long 2.5 T permanent dipole rotating magnets, and on the measurements performed on a scaled down test setup. With the test setup we have improved by about a factor 2 the limit on the parameter $A_e$ describing non linear electrodynamic effects in vacuum: $A_e < 2.9\cdot10^{-21}$ T$^{-2}$ @ 95% c.l.