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Calendar of Physics Talks Vienna
| Observation of Cooper Pairing in a Mesoscopic Fermi Gas |
| Speaker: | Marvin Holten ( Universität Heidelberg, DE) |
| Abstract: | Pairing is the fundamental requirement for fermionic superfluidity and superconductivity. To understand the mechanism behind pair formation is an ongoing challenge in the study of many strongly correlated fermionic systems.
In this talk, I present the direct observation of Cooper pairs in our experiment. We have implemented a fluorescence imaging technique that allows us to extract the full in-situ momentum distribution with single particle and spin resolution. We apply it to a mesoscopic Fermi gas, prepared deterministically in the ground state of a two-dimensional harmonic oscillator. Our ultracold gas allows us to tune freely between a completely non-interaction unpaired system and weak attractions where we find Cooper pair correlations at the Fermi surface. When increasing the interactions even further, the pair character is modified and the pairs gradually turn into tightly bound di |
| Date: | Tue, 16.11.2021 |
| Time: | 09:30 |
| Duration: | 45 min |
| Location: | Atominstitut, Hörsaal |
| Contact: | Julian Leonard |
| Topological defects and generalised orbifolds |
| Speaker: | Ingo Runkel (University of Hamburg) |
| Abstract: | Topological defects in quantum field theory can be understood
as a generalised notion of symmetry, where the operation is not required
to be invertible. Duality transformations are an important example of
this. By considering defects of various dimensions, one is naturally led
to more complicated algebraic structures than just groups. So-called
2-groups are a first instance, which arise from invertible defects of
codimension 1 and 2. Without invertibility one arrives at so-called
"fusion categories”. These structures are already visible in dimension
2, where the field theories are under much better control. I will focus
on two-dimensional conformal field theories and show how these higher
structures arise. I will explain how one can "gauge" such
non-invertible symmetries of 2d CFTs, that is, define a generalised
notion of an orbifold. Finally, time permitting, will briefly discuss
the |
| Date: | Tue, 16.11.2021 |
| Time: | 14:00 |
| Duration: | 60 min |
| Location: | Zoom: https://univienna.zoom.us/j/99228344965?pwd=czNhTjh2ZFNTbzRnN1Z3aG9CdnBmQT09 |
| Contact: | Romain Ruzziconi |
| Influence of Roughness on Sputtering Yields of Surfaces under Ion Bombardment |
| Speaker: | Christian Cupak (TU Wien, Institut für Angewandte Physik) |
| Abstract: | In nuclear fusion devices, the first wall of the reactor is under continuous bombardment by plasma ions. One effect of this bombardment is erosion on the atomic scale, called sputtering. Especially the roughness of the irradiated materials remained a challenging property, which can affect the sputtering yield severely. To better understand this roughness effect, both experiments with a Quartz Crystal Microbalance (QCM) and simulations with the new code SPRAY were performed for samples with very different roughness. A main result was the identification of a new roughness parameter, being the mean surface inclination angle, allowing much better characterisation than other parameters like e.g., the root mean square roughness.
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| Date: | Tue, 16.11.2021 |
| Time: | 16:00 |
| Location: | TU Wien, Institut für Angewandte Physik, E134 1040 Wien, Wiedner Hauptstraße 8-10 Yellow Tower „B“, 5th floor, SEM.R. DB gelb 05 B |
| Contact: | Univ.Prof.Dr. Friedrich Aumayr |
| Sputtering of Mercury and Moon Analogue Material by Solar Wind Ions |
| Speaker: | Herbert Biber (TU Wien, Institut für Angewandte Physik) |
| Abstract: | In the harsh space environment, bodies are continuously exposed to a variety of impactors. The solar wind, a constant stream of ions originating from the sun is one of those. It severely alters the surface properties of planets, moons and asteroids and leads to the emission of particles due to a process called sputtering. This ejection of particles due to impingement of the solar wind is investigated in detail, focusing not only on the total emission of particles, but also on the spatial distribution of ejecta. For this purpose, a catching quartz crystal microbalance technique is used. It furthermore allows for comparison between amorphous analogue films often used for sputtering investigations with realistic, polycrystalline mineral samples. These indicate that amorphous films are well suited for sputtering experiments with planetary analogue samples.
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| Date: | Tue, 16.11.2021 |
| Time: | 16:00 |
| Location: | TU Wien, Institut für Angewandte Physik, E134 1040 Wien, Wiedner Hauptstraße 8-10 Yellow Tower „B“, 5th floor, SEM.R. DB gelb 05 B |
| Contact: | Univ.Prof.Dr. Friedrich Aumayr |
| New approach to (semi)inclusive DIS with QED and QCD factorization |
| Speaker: | Wally Melnitchouk (Jefferson Lab) |
| Abstract: | We present a new factorized approach to inclusive and semi-inclusive deep-inelastic scattering which treats QED and QCD radiationon equal footing,
and provides a systematically improvable approximation to the extraction of collinear and transverse momentum dependent parton distributions.
We demonstrate how the QED contributions can be well approximated by collinear factorization, and illustrate the application of the factorized approach
to QED radiation in inclusive scattering.For semi-inclusive processes, we show how radiation effects prevent a well-defined "photon-hadron" frame
and illustrate the utility of the new method by explicit application to the spin-dependent Sivers and Collins asymmetries.
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| Date: | Tue, 16.11.2021 |
| Time: | 16:15 |
| Duration: | 60 min |
| Location: | ZOOM: https://univienna.zoom.us/j/93427906843?pwd=YjhSejdUVW16QjVQYUh5TVNSNFNhQT09 |
| Contact: | A. Hoang, M. Procura |
| Berry Phases and Wormholes |
| Speaker: | Moritz Dorband (University of Würzburg) |
| Abstract: | We consider Berry phases and entanglement for simple quantum mechanical models as well as for wormholes in gravity and their AdS/CFT interpretation. In both cases the Berry phases arise due to unitary transformations acting on subsystems of the considered models. In the quantum mechanical case where we use a simple model of two coupled spins, we act with a rotation on half of the system, while in the wormhole case, only one throat undergoes time evolution. Since both these transformations are unitary, the entanglement properties of the systems are not distinguishable by a local measurement. On the gravity side, we substantiate the results for the wormhole by an explicit calculation in two-dimensional gravity. We furthermore discuss how Berry phases are related to non-exact symplectic forms in parameter space. Again we consider simple quantum mechanical models and gravity wormholes. |
| Date: | Wed, 17.11.2021 |
| Time: | 13:00 |
| Duration: | 60 min |
| Location: | SEM 9th floor yellow tower, Freihaus, Wiedner Hauptstrasse 8-10, 1040 Vienna |
| Contact: | Daniel Grumiller |
| A Green's function proof of the positive mass theorem |
| Speaker: | Lorenzo Mazzieri (Trento) |
| Abstract: | In this talk we describe a new monotonicity formula holding along the level sets of the Green's function of an asymptotically flat 3-manifold
with nonnegative scalar curvature. Using such a formula, we obtain a simple proof of the celebrated positive mass theorem. In the same context,
and for 1 < p < 3, a Geroch-type calculation is performed along the level sets of p-harmonic functions, leading to a new proof of the Riemannian Penrose Inequality in some case studies.
The results are obtained in collaboration with V. Agostiniani and F. Oronzio. |
| Date: | Thu, 18.11.2021 |
| Time: | 14:00 |
| Duration: | 60 min |
| Location: | ZOOM https://univienna.zoom.us/j/6540036841?pwd=SytyVkZJZzNyRG9lMm13ejlHeHRRUT09 |
| Contact: | Piotr Chrusciel, David Fajman |
| Symmetry Resolved Entanglement in AdS3/CFT2 |
| Speaker: | Suting Zhao (Würzburg) |
| Abstract: | For a QFT with U(1) global symmetry, a resolution of the reduced density matrix via the U(1) subregion-charge defined on the entangled region is allowed. This indicates the existence of a refinement of the usual entanglement entropy, which is the so-called "Symmetry-resolved entanglement entropy(SREE)". In this talk, I will discuss the symmetry-resolved entanglement in the context of AdS3/CFT2. I will start from a toy holographic model: Three-dimensional U(1) Chern-Simons Einstein gravity. The calculations of the SREE rely on the CFT charged moments. I will show that the holographic dual of the CFT charged moments can be simpily realized by inserting a U(1) Wilson line inside the bulk, with its holonomy being identified with the monodromy generated by the boundary vertex operators. The resulting U(1) SREE exhibits a universal equipartition behavior of the entanglement. [...] |
| Date: | Thu, 18.11.2021 |
| Time: | 16:30 |
| Duration: | 60 min |
| Location: | Seminar room 10th floor (yellow tower) |
| Contact: | Daniel Grumiller, Laura Donnay |
| Towards Hamiltonian Learning for Quantum Field Theories |
| Speaker: | Torsten Zache |
| Abstract: | Quantum simulation offers the possibility to study quantum many-body models in regimes that are inaccessible to classical computer simulations. An outstanding problem in this context is the verification of (analog) quantum simulations. In this talk, I will briefly review how to tackle this problem using so-called ``Hamiltonian learning’’. I will then discuss our recent progress towards extending Hamiltonian learning -- which is usually formulated for lattice models -- to continuum field theories. |
| Date: | Fri, 19.11.2021 |
| Time: | 10:30 |
| Location: | Hörsaal ATI https://tuwien.zoom.us/j/99712909944?pwd=dmlybGJYa2tTUWdFQlNNRmJ6YWx3dz09 |
| Contact: | Maximilian Prüfer |
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