CPT

Calendar of Physics Talks Vienna

An asymptotic framework for gravitational scattering
Speaker:Geoffrey Compere (ULB)
Abstract:I will first review the main difficulties in defining scattering in the presence of gravity. I will then outline some concepts useful at defining scattering in asymptotic Minkowski spacetime: a puzzle-piece diagram with 5 asymptotic expansions and 4 overlapping regions that faithfully describe massless and massive fields. I will show in which sense particles, stars and black holes can be described with the same tools in a unified way. I will discuss the BMS covariance that inevitably occurs when gravitational radiation is present and contrast when is BMS symmetry important (to define memory effects) and when it can be bypassed (to define invariant Lorentz charges and intrinsic spin of bodies). I will finally discuss infrared divergences and propose how to regulate them.
Date: Tue, 02.05.2023
Time: 14:00
Duration: 60 min
Location:Erwin-Schroedinger Lecture Hall, Faculty of Physics, Boltzmanngasse 5, 5th floor
Contact:D. Grumiller, S. Fredenhagen, E. Battista, R. Ruzziconi

Triggered Superradiance of an Inverted Spin Ensemble
Speaker:Wenzel Kersten (TU Wien, Atominstitut)
Abstract:In this talk, I will discuss our experimental system that strongly couples a spin ensemble of NV centers in diamond to a novel type of superconducting microwave resonator, exhibiting superradiant behavior. Using this resonator, I am able to invert and stabilize the ensemble, storing the inversion for up to 20 ms – four orders of magnitude longer than the characteristic superradiant timescale. While keeping the ensemble inverted for a prolonged time, the remaining transversal components of the collective spin vector subside via dephasing. What is left are fluctuations that are inherent to the system. When tuning the ensemble back, we thus create an upright metastable inverted state that is very sensitive to incoming radiation. Remarkably, a weak microwave pulse on the order of 10^{-11} photons per spin is sufficient to have an observable effect on the subsequent superradiant decay. I will
Date: Wed, 03.05.2023
Time: 16:15
Duration: 45 min
Location:Hörsaal ATI
Contact:Maximilian Prüfer

Hidden Symmetries and Separability in Rotating Black Hole Spacetimes
Speaker:Finnian Gray (University of Vienna)
Abstract:Stationary Rotating black holes have two kinds of symmetries. The explicit kind which are generated by their timelike and rotation Killing vectors, and the hidden ones which come from Killing tensors.These symmetries are very useful for simplifying physical equations because they allow one to apply a separation of variables ansatz decoupling the PDEs into a set of ODEs. In this talk I will review the general theory of separability in this context and how it applies to the Kerr--NUT--AdS class of spacetimes in any dimension, and moreover to SuGra and string theory inspired black holes. In these cases,the hidden symmetries all descend from one object called the principal tensor. As applications I'll discuss: 1) The separability of Massive vector fields in these spacetimes and the use for e.g. quasi-normal modes 2) the new hidden symmetries of a generic class of slowly rotating black holes
Date: Thu, 04.05.2023
Time: 15:00
Duration: 60 min
Location:TU Wien, Freihaus, Seminar room 10th floor
Contact:Iva Lovrekovic

Testing the gravity-quantum interface with optomechanics and quantum memories
Speaker:Dennis Raetzel (Berlin)
Abstract:It has become one of the major endeavors in physics to understand the interplay between two of our most successful theories, quantum mechanics and general relativity. These efforts have to be guided by experiments and observations at the interface of the two theories. In this talk I will present two specific examples of experimental proposals: a)A potential route to obtain evidence for quantized gravity by employing gravitationally coupled quantum optomechanical sensors [1]. b)An investigation of the effect of gravitational time dilation on photonic states stored in quantum memories [2]. I will also discuss the prospects to perform the corresponding experiments with near-future technology.[1] Plato, A. D. K., Rätzel, D., & Wan, C.(2022). Enhanced Gravitational Entanglement in Modulated Optomechanics. arXiv:2209.12656. [2]Barzel, R., Gündoğan, M., Krutzik, M., Rätzel, D.,& Lämmerzahl C.
Date: Thu, 04.05.2023
Time: 15:30
Duration: 60 min
Location:via zoom https://univienna.zoom.us/j/6540036841?pwd=SytyVkZJZzNyRG9lMm13ejlHeHRRUT09
Contact:P. Chrusciel, D. Fajman

Engineering exotic superfluids with optically-dressed Bose-Einstein condensates
Speaker:Leticia Tarruell (ICFO Barcelona)
Abstract:Spin-orbit coupled Bose-Einstein condensates, where the internal state of the atoms is linked to their momentum through optical coupling, are a flexible experimental platform to engineer synthetic quantum many-body systems. In my talk, I will present recent work where we have exploited the interplay of spin-orbit coupling and tunable interactions in potassium BECs to realize two unconventional superfluid phases. In a first series of experiments, we optically couple two internal states of 39K with very unequal scattering lengths using two-photon Raman transitions. This results in a BEC where the interactions are effectively chiral, i.e. depend on the propagation direction of the atoms. We show that under appropriate conditions the Hamiltonian of the system corresponds to the chiral BF theory: a one-dimensional reduction of the celebrated Chern-Simons gauge that effectively describes frac
Date: Fri, 05.05.2023
Time: 10:00
Duration: 45 min
Location:ATI Hörsaal/https://tuwien.zoom.us/j/93672218922?pwd=dEZNQ2liVzRNNURvNmVWVE5KUWRiQT09
Contact:Julian Leonard