Vacuum Magnetic Birefringence – BMV

We propose to combine state of the art optical instrumentation with very high pulsed magnetic fields to study magneto-optical phenomena in the quantum vacuum i.e. the experimental proof of the magneto optical properties of quantum vacuum. Our goal is to observe for the first time the linear magnetic birefringence of vacuum which corresponds to a variation of the velocity of light depending on its polarisation in the presence of transverse magnetic field. This is one of the very rare macroscopic manifestations of QED vacuum energy that is supposed to fill up our universe and that is one of the natural explanations of the dark energy that accounts for 73% of the total mass-energy of the universe and that permeates all space increasing the rate of expansion of the universe.
The linear magnetic birefringence of vacuum is predicted by QED theory but has not yet been observed. Its observation will be the first evidence of a macroscopic non linear optical effect in vacuum and it will correspond to one of the last remaining tests of QED concerning the photon itself. So far, QED has been tested in bound systems like in the case of the Lamb shift of the hydrogen atom, or in isolated charged particles like in the case of the (g-2) of the electron.
Thanks to the facilities existing at the Laboratoire National des Champs Magnétiques Intenses (LNCMI) in Toulouse and to the technical improvements developed in the recent years, in collaboration with the Laboratoire des Matériaux Avancés (LMA) of Lyon, we are able to advance the frontier of vacuum magneto-optics, and to contribute significantly to quantum electrodynamics, and physics beyond the standard model. To observe this vacuum magnetic birefringence for the first time, an experimental set-up (BMV experiment) based on intense pulsed magnetic field and on a very high finesse Fabry-Perot cavity is operational at the LNCMI. Our magnetic fields are unique in the world and our Fabry-Perot cavity the most challenging ever realized. Precise calibration of the whole apparatus has been performed using helium gas proving our capability to couple a very high finesse cavity to an intense magnetic field. The sensitivity has been improved to reach an unprecedented noise floor for the vacuum magnetic birefringence of Delta-n = 8x10^-21 T^-2 at 3 sigma with about 100 pulses. This first-generation setup has been fully exploited and it finally allowed us to understand its main limits and the improvements that are needed to reach the final goal: a better overall stability of the experiment, a higher magnetic field and a better control of the systematic effects.
The present grant request deals with the design and the development of the second-generation setup. It will allow us to test for the first time if the QED prediction of a Cotton-Mouton effect associated to the vacuum is really present. Our goal is to reach a Delta-n sensitivity per pulse of 27x 10^-23 T^-2 at 1 sigma (8 x 10^-23 T^-2 at 3sigma?. To observe the vacuum magnetic birefringence with a signal to noise ratio equal to 1, 45 pulses will be needed which corresponds to a couple of hours of working time.