title: Experimental comparison of efficient tomography schemes for a six-qubit state.
abstract: Quantum state tomography suffers from the measurement effort increasing exponentially with the number of qubits. Here, we demonstrate permutationally invariant tomography for which, contrary to conventional tomography, all resources scale polynomially with the number of qubits both in terms of the measurement effort as well as the computational power needed to process and store the recorded data. We demonstrate the benefits of combining permutationally invariant tomography with compressed sensing by studying the influence of the pump power on the noise present in a six-qubit symmetric Dicke state, a case where full tomography is possible only for very high pump powers.
authors.affiliation: Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, D-85748 Garching, Germany and Department für Physik, Ludwig-Maximilians-Universität, D-80797 München, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Schwemmer
authors.affiliation: Department of Theoretical Physics, University of the Basque Country UPV/EHU, P.O. Box 644, E-48080 Bilbao, Spain and IKERBASQUE, Basque Foundation for Science, E-48011 Bilbao, Spain and Wigner Research Centre for Physics, Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest, Hungary.
authors.forename: Géza
authors.initials: G
authors.lastname: Tóth
authors.affiliation: School of Physics and Astronomy, University of Birmingham, B15 2TT Birmingham, United Kingdom.
authors.forename: Alexander
authors.initials: A
authors.lastname: Niggebaum
authors.affiliation: Naturwissenschaftlich-Technische Fakultät, Universität Siegen, Walter-Flex-Straße 3, D-57068 Siegen, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Moroder
authors.affiliation: Physikalisches Institut & FDM, Universität Freiburg, Rheinstraße 10, D-79104 Freiburg, Germany.
authors.forename: David
authors.initials: D
authors.lastname: Gross
authors.affiliation: Naturwissenschaftlich-Technische Fakultät, Universität Siegen, Walter-Flex-Straße 3, D-57068 Siegen, Germany.
authors.forename: Otfried
authors.initials: O
authors.lastname: Gühne
authors.affiliation: Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, D-85748 Garching, Germany and Department für Physik, Ludwig-Maximilians-Universität, D-80797 München, Germany.
authors.forename: Harald
authors.initials: H
authors.lastname: Weinfurter