title: Entangling the Whole by Beam Splitting a Part.
abstract: A beam splitter is a basic linear optical element appearing in many optics experiments and is frequently used as a continuous-variable entangler transforming a pair of input modes from a separable Gaussian state into an entangled state. However, a beam splitter is a passive operation that can create entanglement from Gaussian states only under certain conditions. One such condition is that the input light is suitably squeezed. We demonstrate, experimentally, that a beam splitter can create entanglement even from modes which do not possess such a squeezing provided that they are correlated to, but not entangled with, a third mode. Specifically, we show that a beam splitter can create three-mode entanglement by acting on two modes of a three-mode fully separable Gaussian state without entangling the two modes themselves. This beam splitter property is a key mechanism behind the performance of the protocol for entanglement distribution by separable states. Moreover, the property also finds application in collaborative quantum dense coding in which decoding of transmitted information is assisted by interference with a mode of the collaborating party.
authors.affiliation: School of Physics and Astronomy, University of Saint Andrews, North Haugh, Saint Andrews, Fife KY16 9SS, Scotland.
authors.forename: Callum
authors.initials: C
authors.lastname: Croal
authors.affiliation: Max Planck Institute for the Science of Light, Günther-Scharowsky-Straße 1/Building 24, D-91058 Erlangen, Germany.|Institute of Optics, Information and Photonics, University of Erlangen-Nuremberg, Staudtstraße 7/B2, D-91058 Erlangen, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Peuntinger
authors.affiliation: Max Planck Institute for the Science of Light, Günther-Scharowsky-Straße 1/Building 24, D-91058 Erlangen, Germany.|Institute of Optics, Information and Photonics, University of Erlangen-Nuremberg, Staudtstraße 7/B2, D-91058 Erlangen, Germany.
authors.forename: Vanessa
authors.initials: V
authors.lastname: Chille
authors.affiliation: Max Planck Institute for the Science of Light, Günther-Scharowsky-Straße 1/Building 24, D-91058 Erlangen, Germany.|Institute of Optics, Information and Photonics, University of Erlangen-Nuremberg, Staudtstraße 7/B2, D-91058 Erlangen, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Marquardt
authors.affiliation: Max Planck Institute for the Science of Light, Günther-Scharowsky-Straße 1/Building 24, D-91058 Erlangen, Germany.|Institute of Optics, Information and Photonics, University of Erlangen-Nuremberg, Staudtstraße 7/B2, D-91058 Erlangen, Germany.
authors.forename: Gerd
authors.initials: G
authors.lastname: Leuchs
authors.affiliation: School of Physics and Astronomy, University of Saint Andrews, North Haugh, Saint Andrews, Fife KY16 9SS, Scotland.
authors.forename: Natalia
authors.initials: N
authors.lastname: Korolkova
authors.affiliation: Department of Optics, Palacký University, 17. listopadu 1192/12, 77146 Olomouc, Czech Republic.
authors.forename: Ladislav
authors.initials: L
authors.lastname: Mišta