title: Determination of scale-invariant equations of state without fitting parameters: application to the two-dimensional Bose gas across the Berezinskii-Kosterlitz-Thouless transition.
abstract: We present a general "fit-free" method for measuring the equation of state (EoS) of a scale-invariant gas. This method, which is inspired from the procedure introduced by Ku et al. [Science 335, 563 (2012)] for the unitary three-dimensional Fermi gas, provides a general formalism which can be readily applied to any quantum gas in a known trapping potential, in the frame of the local density approximation. We implement this method on a weakly interacting two-dimensional Bose gas across the Berezinskii-Kosterlitz-Thouless transition and determine its EoS with unprecedented accuracy in the critical region. Our measurements provide an important experimental benchmark for classical-field approaches which are believed to accurately describe quantum systems in the weakly interacting but nonperturbative regime.
authors: Institute for Quantum Electronics, ETH Zurich, 8093 Zurich, Switzerland.
authors: Rémi
authors: R
authors: Desbuquois
authors: MIT-Harvard Center for Ultracold Atoms, Research Laboratory of Electronics, Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors: Tarik
authors: T
authors: Yefsah
authors: Laboratoire Kastler Brossel, CNRS, UPMC, ENS, 24 rue Lhomond, F-75005 Paris, France and Collège de France, 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, France.
authors: Lauriane
authors: L
authors: Chomaz
authors: Institut für Laserphysik, Universität Hamburg, Luruper Chaussee 149, D-22761 Hamburg, Germany.
authors: Christof
authors: C
authors: Weitenberg
authors: Laboratoire Kastler Brossel, CNRS, UPMC, ENS, 24 rue Lhomond, F-75005 Paris, France.
authors: Laura
authors: L
authors: Corman
authors: Laboratoire Kastler Brossel, CNRS, UPMC, ENS, 24 rue Lhomond, F-75005 Paris, France.
authors: Sylvain
authors: S
authors: Nascimbène
authors: Laboratoire Kastler Brossel, CNRS, UPMC, ENS, 24 rue Lhomond, F-75005 Paris, France and Collège de France, 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, France.
authors: Jean
authors: J
authors: Dalibard