title: Nonunity gain quantum nondemolition measurements based on measurement and repreparation.
abstract: We demonstrate experimentally a nonunity gain quantum nondemolition measurement based on a simple homodyne measurement and recreation strategy. Although the output state is an amplified version of the input state, the device meets standard criteria for QND measurements: the transfer coefficient was measured to 1.78, and the conditional variance was measured to 0.66.
authors.affiliation: Institut für Optik, Information und Photonik, Max-Plank Forschungsgruppe, Universität Erlangen-Nürnberg, Günther-Scharowsky-Strasse, Erlangen, Germany. schneider@kerr.physik.uni-erlangen.de
authors.forename: Jessica
authors.initials: J
authors.lastname: Schneider
authors.forename: Oliver
authors.initials: O
authors.lastname: Glöckl
authors.forename: Gerd
authors.initials: G
authors.lastname: Leuchs
authors.forename: Ulrik L
authors.initials: UL
authors.lastname: Andersen