title: Multipartite Entanglement Detection with Minimal Effort.
abstract: Certifying entanglement of a multipartite state is generally considered a demanding task. Since an N qubit state is parametrized by 4^{N}-1 real numbers, one might naively expect that the measurement effort of generic entanglement detection also scales exponentially with N. Here, we introduce a general scheme to construct efficient witnesses requiring a constant number of measurements independent of the number of qubits for states like, e.g., Greenberger-Horne-Zeilinger states, cluster states, and Dicke states. For four qubits, we apply this novel method to experimental realizations of the aforementioned states and prove genuine four-partite entanglement with two measurement settings only.
authors.affiliation: Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching, Germany.|Fakultät für Physik, Ludwig-Maximilians-Universität, D-80797 München, Germany.
authors.forename: Lukas
authors.initials: L
authors.lastname: Knips
authors.affiliation: Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching, Germany.|Fakultät für Physik, Ludwig-Maximilians-Universität, D-80797 München, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Schwemmer
authors.affiliation: Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching, Germany.|Fakultät für Physik, Ludwig-Maximilians-Universität, D-80797 München, Germany.
authors.forename: Nico
authors.initials: N
authors.lastname: Klein
authors.affiliation: Institute of Theoretical Physics and Astrophysics, University of Gdańsk, PL-80-952 Gdańsk, Poland.
authors.forename: Marcin
authors.initials: M
authors.lastname: Wieśniak
authors.affiliation: Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching, Germany.|Fakultät für Physik, Ludwig-Maximilians-Universität, D-80797 München, Germany.
authors.forename: Harald
authors.initials: H
authors.lastname: Weinfurter