
Calendar of Physics Talks Vienna
Using Matrix Product States to Classify Quantum Phases in (1+1)D (Vienna Theory Lunch Seminar) 
Speaker:  David Blanik (UniversitÃ¤t Wien) 
Abstract: 
Understanding the phase diagram of correlated quantum manybody systems is among the most important and most challenging tasks towards a comprehensive understanding of such systems. In this talk I will give a brief introduction to tensor networks and explain how to use tensor network methods, in particular Matrix Product States (MPS), to classify gapped quantum phases. Specifically, we will derive the well known classification of symmetryprotected topological (SPT) phases in (1+1)D.
[[This talk is part of the "Vienna Theory Lunch Seminar", a weekly seminar aimed at both graduate and advanced undergraduate students, jointly organized by the University of Vienna and TU Wien. The focus of the seminar is on recent theoretical research done by Master students, PhDs and PostDocs. Free lunch (pizza) will be provided at the seminar. More information: https://lunchseminar.univie.ac.at ]] 
Date:  Tue, 21.11.2023 
Time:  12:30 
Duration:  75 min 
Location:  Boltzmanngasse 5, 5th floor, SchrÃ¶dinger Lecture Hall 
Contact:  Florian Lindenbauer 
Ioninduced Nanopatterning: New Insights from insitu XRay Scattering Studies and Numerical Simulations 
Speaker:  Stefan Facsko (Ion Beam Center, Institute of Ion Beam Physics and Materials Research, HelmholtzZentrum DresdenRossendorf, Dresden/Germany) 
Abstract:  A plethora of selforganized nanoscale patterns emerge on surfaces which are irradiated by lowenergy ion beams. Depending on the irradiation conditions, hexagonally ordered dot or pit patterns, checkerboard patterns, as well as periodic ripple patterns are formed spontaneously due to the nonequilibrium conditions induced by continuous ion irradiation. Insitu studies of the surface morphology can reveal the kinetics of the patterning process, yielding further insight into the dominant mechanisms and thus enabling to gain precise process control. For instance, by realtime insitu Grazing Incidence Small Angle XRay Scattering (GISAXS) investigation the significant morphological parameters of the surface are deduced, thus tracking the development of the crystalline Ge(100) surface morphology during ion irradiation. Observing the kinetics of pattern formation in the nonlinear regime, we 
Date:  Tue, 21.11.2023 
Time:  16:00 
Location:  TU Wien, Institut fÃ¼r Angewandte Physik, E134 1040 Wien, Wiedner HauptstraÃe 810 Yellow Tower âBâ, 5th floor, SEM.R. DB gelb 05 B 
Contact:  Prof. Dr. Richard Wilhelm 
Rigidity of extremal horizons and black hole uniqueness 
Speaker:  James Lucietti (Edinburgh) 
Abstract:  I will present a recent proof which shows that the intrinsic geometry of compact crosssections of any vacuum extremal horizon, possibly with a cosmological constant, must admit a Killing vector field.
In particular, this implies that the extremal Kerr horizon is the most general such horizon in fourdimensional General Relativity and completes the classification of the associated nearhorizon geometries.
I will also discuss a recent uniqueness proof which shows that any analytic Einstein spacetime, that contains a static extremal horizon with a maximally symmetric compact crosssection,
is the extremal Schwarzschild de Sitter spacetime or its nearhorizon geometry. 
Date:  Wed, 22.11.2023 
Time:  14:15 
Duration:  60 min 
Location:  Seminarraum A, Waehringer StraÃe 17, 2. Stock 
Contact:  P. Chrusciel, D. Fajman 
Fiber FabryPÃ©rot Fabrication for Enhanced AtomCavity Coupling 
Speaker:  Isabelle Safa (TU Wien, Atominstitut) 
Abstract:  Cold atoms are a leading platform for quantum computation thanks to their coherence properties, microscopic controllability, and scalability. While current quantum processors with neutral atoms are limited to local interactions, our experiment aims to reach programmable and large scale connectivity between Rubidium atoms by means of optical cavitygenerated interactions. For this purpose, a small yet open cavity with compact mode geometry is required. Suitable devices are thereupon fiber FabryPÃ©rot cavities (FFPC), the mirrors of which are directly machined on the end facets of two facetoface optical fibers. These micrometerscale, concave mirrors thus form a miniaturized FabryPÃ©rot interferometer. In this talk, I will present the work done during my master thesis at the ATI in the group of Julian LÃ©onard, in which I started to build a setup for this micromirror machining. The proce 
Date:  Wed, 22.11.2023 
Time:  16:15 
Duration:  45 min 
Location:  Helmut Rauch HÃ¶rsaal ATI 
Contact:  Julian Leonard 
SPATIAL CURVATURE, DARK ENErGY DYNAMICS, NEITHER, or BOTH 
Speaker:  Bharat Ratra (Kansas State University) 
Abstract:  Experiments and observations over the last two decades have provided strong support for a "standard" model of cosmology that describes the evolution of the universe from an early epoch of inflation to the complex hierarchy of structure seen today. I review the basic physics, astronomy, and history of ideas, on which this model is based. I describe the data which persuade cosmologists that (as yet not directly detected) dark energy and dark matter are by far the main components of the energy budget of the universe. I conclude with a list of open cosmological questions. 
Date:  Thu, 23.11.2023 
Time:  17:00 
Location:  Technische Universitaet Wien, Freihaus, Hoersaal 5, Wiedner Hauptstrasse 8, 1040 Wien 
Contact:  Prof. Hartmut Abele 
Quantum Field Simulator: From Cosmology via RamsauerTownsend Effect to Supersolids 
Speaker:  Markus Oberthaler (UniversitÃÂ¤t Heidelberg) 
Abstract:  Recently it has been shown that two dimensional ultracold gases allow for the study of time dependent curved spacetime of the form discussed in cosmology. With the assumption of homogeneity and isotropy of the universe the metric for large scale is given by the FriedmannLemaitreRobertsonWalker metric, which is characterized via the sign of the curvature and a general scale factor. I will discuss how both, the curvature as well as the scale factor, are experimentally accessible with ultracold gases leading to curved trajectories as well as to particle production in an expanding universe [1]. How the particle production can be connected to the RamsauerTownsend effect will be presented and motivates the study of oscillating â expanding and compressing â universes. This regime leads to emergent nonlinear structures of spacetime indicating that backaction is already present in the expe 
Date:  Fri, 24.11.2023 
Time:  10:00 
Duration:  45 min 
Location:  Helmut Rauch HÃÂ¶rsaal ATI 
Contact:  Julian Leonard 
