Observation of magneto-electric non-reciprocity in molecular nitrogen gas

Abstract

We report the direct observation of the non-reciprocity of the velocity of light, induced in a gas by electric and magnetic fields. This bilinear magneto-electro-optical phenomenon appears in the presence of crossed electric and magnetic fields perpendicular to the light wavevector, as a refractive index difference between two counterpropagating directions. Using a high finesse ring cavity, we have measured this magneto-electric non-reciprocity in molecular Nitrogen at ambient temperature and atmospheric pressure; for light polarized parallel to the magnetic field it is 2η exp (N2) = (4.7 ± 1) × 10 −23 m.V −1 .T −1 for λ = 1064 nm, in agreement with the expected order of magnitude. Our measurement opens the way to a deeper insight into light-matter interaction, since bilinear magneto-electric effects correspond to a coupling beyond the electric dipole approximation. We were able to measure a magneto-electric non-reciprocity as small as ∆n = (5 ± 2) × 10 −18 , which makes its observation in quantum vacuum a conceivable challenge.