In physics, vacuum has historically been defined as a region of space where light travels at the well-known calculated constant, c. In the early 20th century, the quantization of electromagnetism led to the development of the now well-tested theoretical framework of quantum electrodynamics (QED). An interesting, yet untested, prediction of QED is the non-constant, even anisotropic, propagation of light through vacuum. The origin of this anisotropy is that, in contrast to classical vacuum, QED vacuum can be polarized in the presence of an external electromagnetic field resulting in a birefringent vacuum, nvac.
The leading experiments in the field, PVLAS (Polarizzazione del Vuoto con LASer; Ferrara, Italy)and BMV (Birefringence Magnetique du Vide; Toulouse, France), seek to measure this effect experimentally by observing the ellipticity induced in a linearly polarized laser field propagating through a region of birefringent vacuum. The BMV experiment, housed at the Laboratoire National des Champs Magnetique Intenses (LNCMI) in Toulouse, France, utilises high-amplitude (B 20T) pulsed magnetic fields in its efforts to measure vacuum polarization.
The main challenge of the experiment lies in reaching the sensitivity required to measure the minute birefringence, nvac = kvacB2, resulting from the small magnetic-birefringence constant of vacuum (kvac 4 × 10−24 T−2) predicted by QED; a number which, as a result of the recent advancements in state-of-the-art precision interferometry owing largely to the successes of interferometric gravitational-wave detectors, is increasingly viable. The BMV collaboration seeks to accomplish this goal on two fronts: first, through collaboration with the LNCMI facility in the implementation of novel magnet technologies for signal production; and second, through the development and characterization of an ultra-precise polarimeter for signal detection. Here we present the status of the BMV experiment and the perspectives for the near future.
