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View of the apparatus at the LNL INFN lab in Legnaro
(Padua, Italy)

apparatus in the Physics. Dept. at

View of the prototype apparatus in the Physics Dept. of the
University of Ferrara

Nonlinear effects in electromagnetic processes in vacuum have been sought after for many years after having been predicted by Euler and Heisenberg in their effective Lagrangian published in 1936. The only input to their calculation was the Heisenberg uncertainty principle leading to virtual pair creation, which allowed photons to interact with each other.

The direct measurement of this effect is yet to be seen and has been the aim of the PVLAS experiment since its beginnings. The PVLAS experiment, financed by the Italian Istituto Nazionale di Fisica Nucleare (INFN), is located at the Laboratori Nazionali di Legnaro of INFN (LNL), Padova, Italy (old site) and in the Physics Dept. of the Ferrara University (new site).

The LNL setup consists of a sensitive ellipsometer attempting to detect the small changes in the polarization state of light propagating through a 1 m long magnetic field region in vacuum. It is based on a high finesse Fabry-Perot cavity and a superconducting 5 T rotating dipole magnet. Indeed, vacuum will become birefringent in the presence of a strong magnetic field. A possible secondary effect, which could mask the vacuum magnetic birefringence, could be due to the existence of a light, neutral pseudoscalar/scalar particle coupling to two photons via the Primakoff effect.

The Ferrara prototype setup is similar, but the ellipsometer has a horizontal axis (instead of vertical as in LNL), and the experiment utilizes permanent magnets.

Panorama view of the experiment (2006) at the LNL INFN laboratory
Panorama view of the experiment (2008) at the LNL INFN laboratory

Check this link for a more detailed review of the experiment, and this link for a list of past and present members of PVLAS.

Additional information

Webmaster: Edoardo Milotti, e-mail: milotti at ts.infn.it - Last update: November 2012