title: Upper Bounds on Spontaneous Wave-Function Collapse Models Using Millikelvin-Cooled Nanocantilevers.
abstract: Collapse models predict a tiny violation of energy conservation, as a consequence of the spontaneous collapse of the wave function. This property allows us to set experimental bounds on their parameters. We consider an ultrasoft magnetically tipped nanocantilever cooled to millikelvin temperature. The thermal noise of the cantilever fundamental mode has been accurately estimated in the range 0.03-1 K, and any other excess noise is found to be negligible within the experimental uncertainty. From the measured data and the cantilever geometry, we estimate the upper bound on the continuous spontaneous localization collapse rate in a wide range of the correlation length r_{C}. Our upper bound improves significantly previous constraints for r_{C}>10^{-6}  m, and partially excludes the enhanced collapse rate suggested by Adler. We discuss future improvements.
authors.affiliation: Istituto Nazionale di Fisica Nucleare (INFN), TIFPA, I-38123 Povo, Trento, Italy.|Istituto di Fotonica e Nanotecnologie, CNR-Fondazione Bruno Kessler, I-38123 Povo, Trento, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Vinante
authors.affiliation: Department of Physics, University of Trieste, Strada Costiera 11, 34014 Trieste, Italy.|Istituto Nazionale di Fisica Nucleare (INFN), Trieste Section, Via Valerio 2, 34127 Trieste, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Bahrami
authors.affiliation: Department of Physics, University of Trieste, Strada Costiera 11, 34014 Trieste, Italy.|Istituto Nazionale di Fisica Nucleare (INFN), Trieste Section, Via Valerio 2, 34127 Trieste, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Bassi
authors.affiliation: Leiden Institute of Physics, Leiden University, Post Office Box 9504, 2300 RA Leiden, The Netherlands.
authors.forename: O
authors.initials: O
authors.lastname: Usenko
authors.affiliation: Leiden Institute of Physics, Leiden University, Post Office Box 9504, 2300 RA Leiden, The Netherlands.
authors.forename: G
authors.initials: G
authors.lastname: Wijts
authors.affiliation: Leiden Institute of Physics, Leiden University, Post Office Box 9504, 2300 RA Leiden, The Netherlands.
authors.forename: T H
authors.initials: TH
authors.lastname: Oosterkamp