title: Observing the ultrafast buildup of a Fano resonance in the time domain.
abstract: Although the time-dependent buildup of asymmetric Fano line shapes in absorption spectra has been of great theoretical interest in the past decade, experimental verification of the predictions has been elusive. Here, we report the experimental observation of the emergence of a Fano resonance in the prototype system of helium by interrupting the autoionization process of a correlated two-electron excited state with a strong laser field. The tunable temporal gate between excitation and termination of the resonance allows us to follow the formation of a Fano line shape in time. The agreement with ab initio calculations validates our experimental time-gating technique for addressing an even broader range of topics, such as the emergence of electron correlation, the onset of electron-internuclear coupling, and quasi-particle formation.
authors.affiliation: Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Kaldun
authors.affiliation: Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Blättermann
authors.affiliation: Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany.
authors.forename: V
authors.initials: V
authors.lastname: Stooß
authors.affiliation: Institute for Theoretical Physics, Vienna University of Technology, Wiedner Hauptstraße 8, 1040 Vienna, Austria.
authors.forename: S
authors.initials: S
authors.lastname: Donsa
authors.affiliation: Department of Physics, Kansas State University, 230 Cardwell Hall, Manhattan, KS 66506, USA.
authors.forename: H
authors.initials: H
authors.lastname: Wei
authors.affiliation: Institute for Theoretical Physics, Vienna University of Technology, Wiedner Hauptstraße 8, 1040 Vienna, Austria.
authors.forename: R
authors.initials: R
authors.lastname: Pazourek
authors.affiliation: Institute for Theoretical Physics, Vienna University of Technology, Wiedner Hauptstraße 8, 1040 Vienna, Austria.
authors.forename: S
authors.initials: S
authors.lastname: Nagele
authors.affiliation: Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Ott
authors.affiliation: Department of Physics, Kansas State University, 230 Cardwell Hall, Manhattan, KS 66506, USA.
authors.forename: C D
authors.initials: CD
authors.lastname: Lin
authors.affiliation: Institute for Theoretical Physics, Vienna University of Technology, Wiedner Hauptstraße 8, 1040 Vienna, Austria.
authors.forename: J
authors.initials: J
authors.lastname: Burgdörfer
authors.affiliation: Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany. thomas.pfeifer@mpi-hd.mpg.de.|Center for Quantum Dynamics, Universität Heidelberg, 69120 Heidelberg, Germany, EU.
authors.forename: T
authors.initials: T
authors.lastname: Pfeifer