title: Quantum Nondemolition Measurement Enables Macroscopic Leggett-Garg Tests.
abstract: We show how a test of macroscopic realism based on Leggett-Garg inequalities (LGIs) can be performed in a macroscopic system. Using a continuous-variable approach, we consider quantum nondemolition (QND) measurements applied to atomic ensembles undergoing magnetically driven coherent oscillation. We identify measurement schemes requiring only Gaussian states as inputs and giving a significant LGI violation with realistic experimental parameters and imperfections. The predicted violation is shown to be due to true quantum effects rather than to a classical invasivity of the measurement. Using QND measurements to tighten the "clumsiness loophole" forces the stubborn macrorealist to recreate quantum backaction in his or her account of measurement.
authors.affiliation: Naturwissenschaftlich-Technische Fakultät, Universität Siegen, Walter-Flex-Str. 3, D-57068 Siegen, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Budroni
authors.affiliation: Department of Theoretical Physics, University of the Basque Country UPV/EHU, P.O. Box 644, E-48080 Bilbao, Spain.
authors.forename: G
authors.initials: G
authors.lastname: Vitagliano
authors.affiliation: ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels, Barcelona, Spain.
authors.forename: G
authors.initials: G
authors.lastname: Colangelo
authors.affiliation: ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels, Barcelona, Spain.
authors.forename: R J
authors.initials: RJ
authors.lastname: Sewell
authors.affiliation: Naturwissenschaftlich-Technische Fakultät, Universität Siegen, Walter-Flex-Str. 3, D-57068 Siegen, Germany.
authors.forename: O
authors.initials: O
authors.lastname: Gühne
authors.affiliation: Department of Theoretical Physics, University of the Basque Country UPV/EHU, P.O. Box 644, E-48080 Bilbao, Spain.|IKERBASQUE, Basque Foundation for Science, E-48013 Bilbao, Spain.|Wigner Research Centre for Physics, Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest, Hungary.
authors.forename: G
authors.initials: G
authors.lastname: Tóth
authors.affiliation: ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels, Barcelona, Spain.|ICREA-Institució Catalana de Recerca i Estudis Avançats, 08015 Barcelona, Spain.
authors.forename: M W
authors.initials: MW
authors.lastname: Mitchell