title: Witnessing effective entanglement over a 2 km fiber channel.
abstract: We present a fiber-based continuous-variable quantum key distribution system. In the scheme, a quantum signal of two non-orthogonal weak optical coherent states is sent through a fiber-based quantum channel. The receiver simultaneously measures conjugate quadratures of the light using two homodyne detectors. From the measured Q-function of the transmitted signal, we estimate the attenuation and the excess noise caused by the channel. The estimated excess noise originating from the channel and the channel attenuation including the quantum efficiency of the detection setup is investigated with respect to the detection of effective entanglement. The local oscillator is considered in the verification. We witness effective entanglement with a channel length of up to 2 km.
authors.affiliation: Max Planck Institute for the Science of Light, Günther-Scharowsky-Str 1 / Bau 24, 91058 Erlangen, Germany. Christoffer.Wittmann@mpl.mpg.de
authors.forename: Christoffer
authors.initials: C
authors.lastname: Wittmann
authors.forename: Josef
authors.initials: J
authors.lastname: Fürst
authors.forename: Carlos
authors.initials: C
authors.lastname: Wiechers
authors.forename: Dominique
authors.initials: D
authors.lastname: Elser
authors.forename: Hauke
authors.initials: H
authors.lastname: Häseler
authors.forename: Norbert
authors.initials: N
authors.lastname: Lütkenhaus
authors.forename: Gerd
authors.initials: G
authors.lastname: Leuchs