title: Direct measurement of superluminal group velocity and signal velocity in an optical fiber.
abstract: We present an easy way of observing superluminal group velocities using a birefringent optical fiber and other standard devices. In the theoretical analysis, we show that the optical properties of the setup can be described using the notion of "weak value." The experiment shows that the group velocity can indeed exceed c in the fiber; and we report the first direct observation of the so-called "signal velocity," the speed at which information propagates and that cannot exceed c.
authors.affiliation: Group of Applied Physics, University of Geneva, 20 rue de l'Ecole-de-Médecine, CH-1211 Geneva 4, Switzerland.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Brunner
authors.forename: Valerio
authors.initials: V
authors.lastname: Scarani
authors.forename: Mark
authors.initials: M
authors.lastname: Wegmüller
authors.forename: Matthieu
authors.initials: M
authors.lastname: Legré
authors.forename: Nicolas
authors.initials: N
authors.lastname: Gisin