title: Reversing the pump dependence of a laser at an exceptional point.
abstract: When two resonant modes in a system with gain or loss coalesce in both their resonance position and their width, a so-called exceptional point occurs, which acts as a source of non-trivial physics in a diverse range of systems. Lasers provide a natural setting to study such non-Hermitian degeneracies, as they feature resonant modes and a gain material as their basic constituents. Here we show that exceptional points can be conveniently induced in a photonic molecule laser by a suitable variation of the applied pump. Using a pair of coupled microdisk quantum cascade lasers, we demonstrate that in the vicinity of these exceptional points the coupled laser shows a characteristic reversal of its pump dependence, including a strongly decreasing intensity of the emitted laser light for increasing pump power.
authors.affiliation: 1] Photonics Institute, Vienna University of Technology, A-1040 Vienna, Austria [2] Center for Micro- and Nanostructures, Vienna University of Technology, A-1040 Vienna, Austria [3].
authors.forename: M
authors.initials: M
authors.lastname: Brandstetter
authors.affiliation: 1] Institute for Theoretical Physics, Vienna University of Technology, A-1040 Vienna, Austria [2].
authors.forename: M
authors.initials: M
authors.lastname: Liertzer
authors.affiliation: 1] Photonics Institute, Vienna University of Technology, A-1040 Vienna, Austria [2] Center for Micro- and Nanostructures, Vienna University of Technology, A-1040 Vienna, Austria.
authors.forename: C
authors.initials: C
authors.lastname: Deutsch
authors.affiliation: 1] Center for Micro- and Nanostructures, Vienna University of Technology, A-1040 Vienna, Austria [2] Institute for Solid-State Electronics, Vienna University of Technology, A-1040 Vienna, Austria.
authors.forename: P
authors.initials: P
authors.lastname: Klang
authors.affiliation: Institute for Analysis and Scientific Computing, Vienna University of Technology, A-1040 Vienna, Austria.
authors.forename: J
authors.initials: J
authors.lastname: Schöberl
authors.affiliation: Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: H E
authors.initials: HE
authors.lastname: Türeci
authors.affiliation: 1] Center for Micro- and Nanostructures, Vienna University of Technology, A-1040 Vienna, Austria [2] Institute for Solid-State Electronics, Vienna University of Technology, A-1040 Vienna, Austria.
authors.forename: G
authors.initials: G
authors.lastname: Strasser
authors.affiliation: 1] Photonics Institute, Vienna University of Technology, A-1040 Vienna, Austria [2] Center for Micro- and Nanostructures, Vienna University of Technology, A-1040 Vienna, Austria.
authors.forename: K
authors.initials: K
authors.lastname: Unterrainer
authors.affiliation: Institute for Theoretical Physics, Vienna University of Technology, A-1040 Vienna, Austria.
authors.forename: S
authors.initials: S
authors.lastname: Rotter