title: Signal velocity, causality, and quantum noise in superluminal light pulse propagation.
abstract: We consider pulse propagation in a linear anomalously dispersive medium where the group velocity exceeds the speed of light in vacuum ( c) or even becomes negative. A signal velocity is defined operationally based on the optical signal-to-noise ratio, and is computed for cases appropriate to the recent experiment where such a negative group velocity was observed. It is found that quantum fluctuations limit the signal velocity to values less than c.
authors.affiliation: NEC Research Institute, 4 Independence Way, Princeton, New Jersey 08540, USA.
authors.forename: A
authors.initials: A
authors.lastname: Kuzmich
authors.forename: A
authors.initials: A
authors.lastname: Dogariu
authors.forename: L J
authors.initials: LJ
authors.lastname: Wang
authors.forename: P W
authors.initials: PW
authors.lastname: Milonni
authors.forename: R Y
authors.initials: RY
authors.lastname: Chiao