Agathe Cadène, LNCMI Toulouse, France

Agatha Cadene

I have done physical and chemical sciences studies at the University Paul Sabatier, Toulouse. I first obtained a teaching degree which allows me to be a professor in high school (agrégation de physique). Before starting my work as a teacher, I decided to do a PhD at the LNCMI Toulouse in order to widen my field of knowledge and develop scientific skills, which will be useful for my future job.

I work on the BMV (Biréfringence Magnétique du Vide) experiment. The aim of this project is to measure the birefringence induced by a transverse magnetic field in vacuum. This effect exists in any medium and is known as the Cotton-Mouton effect. In the framework of quantum electrodynamics (QED) it was predicted to exist also in vacuum. The value of the magnetic birefringence of vacuum is expected to be 4×10-24 for an applied magnetic field of 1 T.

The measurement of this birefringence is made via an ellipticity measurement. The principle is to linearly polarize a laser beam. The light then propagates in the vacuum where a transverse magnetic field is applied. Under the field’s effect, the linear polarization becomes elliptical. The ellipticity we measure is proportional to the square of the magnetic field and to the length on which it is applied. These two parameters have thus to be as high as possible. This is why the LNCMI designed a special coil named X-coil, which can provide a maximum transverse field of 14 T over a length of 0.14 m. This setup also allows to perform measurements in gases, which constitute quantum chemistry tests.  

This PhD work is very interesting for me. It allows me to learn on various subjects such as pulsed fields, optics (in particular high-finesse Fabry-Pérot cavity), electronics (frequency locking of the laser), high-precision measurements, etc. Moreover, I have the opportunity to teach at the university, which is a part of my work I enjoy very much.