title: Magnetoelectric directional nonreciprocity in gas-phase molecular nitrogen.
abstract: We report the direct observation of the nonreciprocity of the velocity of light, induced by electric and magnetic fields. This bilinear magneto-electro-optical effect appears in crossed electric and magnetic fields perpendicular to the light wave vector, as a refractive index difference between two counterpropagating directions. Using a high finesse ring cavity, we have measured this magnetoelectric nonreciprocity 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 beyond the electric dipole approximation. We were able to measure a nonreciprocity as small as Δn =(5±2)×10(-18), which makes its observation in quantum vacuum a conceivable challenge.
authors.affiliation: Université de Toulouse, UPS, Laboratoire Collisions Agrégats Réactivité, IRSAMC, F-31062 Toulouse, France.
authors.forename: B
authors.initials: B
authors.lastname: Pelle
authors.forename: H
authors.initials: H
authors.lastname: Bitard
authors.forename: G
authors.initials: G
authors.lastname: Bailly
authors.forename: C
authors.initials: C
authors.lastname: Robilliard