Abteilung für Teilchen- & Astroteilchen-Physik
 
 

Seminars, Colloquia and Events

Period from 20 May 2025 to 03 June 2025


Wednesday, 21 May 2025

  09:30 Seminar Dynamik und Struktur von Atomen und Molekülen
Patrick Friebel, Ultrafast Liquid Crystal Dynamics
THz vibrational dynamics of Liquid Crystals: from molecular origin to bulk response
Central Seminar Room, library building
  11:15 Bothe-Kolloquium
Birgit Stiller, Max Planck Institute for the Science of Light
Sounds waves harnessing optical quantum technologies and photonic machine learning
Central seminar room, library building
Photonics has the potential to advance modern quantum technologies and high-speed applications such as communications and the processing of large amounts of data. However, to replace or improve the well-established systems with photonic solutions, there is still a way to go. A promising approach to manipulate light all-optically is to use the link of optical waves with acoustic vibrations. Our research experimentally investigates how traveling sound waves can be used to process states of light in the classical and quantum regime. With the help of acoustic waves, we implement several building blocks and operators for photonic machine learning, such as an optoacoustic recurrent operator and a photonic activation function for all-optical neural networks. We demonstrate non-reciprocal processing of polarization and orbital angular momentum states and show how photon-phonon entanglement and phonon cooling via stimulated Brillouin scattering is implemented in continuum systems like waveguides and optical fibers.
  14:15 Kosmologie und Elementarteilchenphysik
Matteo Fontana
General Relativistic Models of Disc Galaxies
Institut für Theoretische Physik, Phil12;SR105 (Note unusual date, Tunch schedule)
Galaxy dynamics have long been understood within the framework of Newtonian mechanics, where the low velocities and weak gravitational fields suggest that Einstein’s general relativity (GR) plays only a minor role. However, the struggle to explain the nearly flat rotation curves in disc galaxies historically called for the invocation of dark matter (DM), a non-baryonic matter component that has not yet been detected directly. Even though DM also plays a central role in the Lambda CDM cosmological model, its elusive nature has motivated alternative explanations, including Modified Newtonian Dynamics and Modified Gravity theories. Nevertheless, GR itself offers a compelling alternative due to the non-linear nature of the Einstein Equations (EE) and the additional degrees of freedom it introduces. Among the most significant effects these features give rise to frame dragging, which becomes particularly relevant in extended, rotating systems. In this talk I will present the ( eta, H) models corresponding to exact solutions to the EE for a stationary, axisymmetric spacetime that describe a rotating disc of dust. These models offer an effective representation of disc galaxies in regions where both the assumed symmetries and the dust approximation hold, that is, far from the rotation axis and close to the galactic plane. I will then emphasize the crucial impact of the choice of reference frame on the predicted rotation curves, focusing on the rigidly rotating dust limit known as Balasin-Grumiller model. When analyzed by Zero Angular Momentum Observers (ZAMOs), this model reproduces flat rotation curves of the Milky Way without invoking dark matter. Finally, I will show how the nonlinearity of GR can produce observable deviations from Newtonian gravity on large scales, under non-relativistic conditions by introducing Asymptotically Conically Minkowskian (ACM) spacetimes, characterized by a locally flat but conical geometry at large distances. These topological features could be probed by (1) measuring holonomy via parallel transport of a test vector around the symmetry axis, (2) detecting angular-deficit signatures in gravitational lensing, and (3) analyzing scalar-field propagation to uncover vacuum-state ambiguities.
  16:30 Zentrum für Quantendynamik Kolloquium
Dr. Simon Jäger
Quantum technologies using cavity-mediated interactions and dissipation
Physikalisches Institut, INF 226, K 1-3
  17:00 SFB1225 ISOQUANT
Federica Capellino
Meet&Mingle@ISOQUANT: Networking and Mentoring platform for FLINTA* students in physics
Institut für Theoretische Physik, PI, seminar box 1. floor
tba

Thursday, 22 May 2025

  11:15 Teekolloquium
Prof. Dr. Thorsten Schumm
Optical Mössbauer spectroscopy of Th-229 in CaF crystals
Grosser Hoersaal/Big Lecture Hall (library)
The recent precision VUV laser spectroscopy of Thorium-229 doped into calcium fluoride single crystals allows to probe nuclear properties and host material parameters with unprecedented accuracy. In this talk I will resume our current understanding of the microscopic doping structure, combining theoretical modelling, solid-state techniques like XAFS and RBS, and precision laser spectroscopy. We also report quenching of the thorium-229 isomer population under X-ray and laser illumination in the VUV, UV and optical range, hinting towards strong and controllable coupling of nuclear and solid-state degrees of freedom.
    ARI Institute Colloquium
Annalisa Pillepich
Simulating galaxies from dwarfs to clusters -- the diverse and far-reaching effects of super massive black holes
ARI, Moenchhofstrasse 12-14, Seminarraum 1.OG
Simulating galaxies from dwarfs to clusters — the diverse and far-reaching effects of super massive black holes over the past two decades, it has become clear that energetic feedback from supermassive black holes (SMBHs) is a fundamental ingredient in our models of galaxy formation and evolution. From quenching star formation in massive galaxies to regulating the properties of the circumgalactic and intracluster media, SMBH-driven processes manifest across a wide range of scales and environments. In this talk, I will present recent advances in our understanding of the diverse and far-reaching effects of SMBH feedback, as revealed by state-of-the-art cosmological simulations. I will begin by introducing the simulations themselves — in particular, the IllustrisTNG project, which I have co-led and developed, and which has become a benchmark in extragalactic modeling for both observers and theorists alike. Using results from the IllustrisTNG simulation suite and its successors, I will demonstrate how a unified set of physical models can simultaneously reproduce realistic galaxy populations while predicting the thermodynamical, ionization, and chemical properties of cosmic gas on halo and intergalactic scales. I will highlight how feedback leaves its most direct and distinctive imprints not on the stars, but on the surrounding gas — influencing its temperature, kinematics, metal enrichment, and X-ray emission. In particular, I will contrast the effects of SMBH feedback in star-forming versus quiescent galaxies, highlighting how their gaseous atmospheres bear the signatures of these energetic processes. I will conclude by providing a diversity of insights and predictions for the gaseous haloes of galaxies spanning five orders of magnitude in mass, illustrating how SMBH feedback shapes the circumgalactic, intragroup, and intracluster media.
  13:30 Special Seminar
Prof. Dr. Thorsten Schumm
Coffee break and Q&A session with Thorsten Schumm for young scientists
Zentraler Seminarraum / Central seminar room (library)
  16:15 Teilchen-Tee
Ben Freivogel
Quantum Gravity Effects at Long Distance Scales
Institut für Theoretische Physik, Phil12, SR106
I will present situations where quantum gravity effects are significant at distances much longer than the Planck scale. I will discuss to what extent we can hope to measure these effects.

Friday, 23 May 2025

  10:30 Special Seminar
Dr. Alex Kim (Lawrence Berkeley National Laboratory, USA, CA)
Measuring type Ia supernova angular-diameter distances with intensity interferometry
Zentraler Seminarraum / Central seminar room (library building)
Abstract: Intensity interferometry, based on the Hanbury Brown-Twiss effect, has the potential to measure supernova sizes and distances. With optimized telescope positioning, observing strategy, and advancements in single-photon detection technology, this method can provide precise angular size measurements of supernovae with apparent magnitudes as bright as 12~mag. For type~Ia supernovae, this limiting brightness corresponds to a local volume extending to redshift z ~0.004 and an anticipated discovery rate of approximately 1 event per year. The combination of angular size data with known physical dimensions enables accurate distance determination. As type Ia supernovae serve as standardizable candles for measuring the Universe's expansion history, combining intensity interferometry distances with the supernova Hubble diagram facilitates measurements of the Hubble constant I will also briefly discuss recent BAO measurements by the DESI collaboration, the connection with Type Ia supernovae, and peculiar velocities.
  17:00 Physikalisches Kolloquium
Prof. Dr. Thorsten Schumm
Nuclear Physics with a laser – the story of Thorium-229
KIP, INF 227, Hörsaal 1

Among all known isotopes, Thorium-229 has the lowest nuclear excited state, only 8.4 eV above the ground state. This so-called “isomer” is accessible to VUV laser excitation and a multitude of applications at the interface of atomic and nuclear physics have been proposed, including a nuclear clock, a gamma laser and a sensitive detector for variations of fundamental constants. After decades of attempts to determine the exact isomer energy and other nuclear properties, we report on two experiments which resonantly excite the isomer by lasers and spectroscopically resolve the nuclear quadrupole splitting in a single crystal environment. This allows us to determine the sensitivity of the nuclear clock transition to variations of the fine structure constant, which exceeds all schemes involving electron shell transitions by 3 orders of magnitude.


Monday, 26 May 2025

  16:15 Theoretisch-Physikalisches Kolloqium
Christof Wetterich
The Probabilistic World
Institut für Theoretische Physik, Phil19
We propose that the Universe is described by a classical statistical probability distribution for events at all positions and times. Quantum mechanics and quantum field theory follow by the focus on time hyper-surfaces. In this contribution to the “philosophical seminar series” we show the emergence of wave functions and a time evolution according to the Schrödinger equation for suitable generalised Ising models which correspond to probabilistic cellular automata. Quantum mechanics can be embedded in classical statistics, with all quantum laws arising from the simple standard laws for classical probabilities. The power of the quantum formalism for the dynamics of probabilistic cellular automata is demonstrated by a numerical simulation.

Tuesday, 27 May 2025

  11:15 Seminar Theoretische Quantendynamik
Zewen Sun, MPIK
Reevaluating Pb-208 Nuclear Charge Radius
Seminar room 242, Bothe Lab
  14:15 Kosmologie und Elementarteilchenphysik
Benedikt Schosser
Markov Walk Exploration of Model Spaces: Bayesian Selection of Dark Energy Models with Supernovae
Institut für Theoretische Physik, Phil19
Making an informed choice between competing physical models becomes increasingly important in the era of precision cosmology. Central to model selection is a trade-off between performing a good fit and low model complexity: A model of higher complexity should only be favoured over a simpler model if it provides significantly better fits. In Bayesian terms, this can be achieved by considering the evidence ratio, enabling choices between two competing models. We generalise this concept by constructing Markovian random walks in model space governed by the logarithmic evidence ratio. This is in analogy to the logarithmic likelihood ratio in parameter estimation problems. We apply our methodology to selecting a polynomial for the dark energy equation of state function based on data for the supernova distance-redshift relation.
  16:30 Heidelberg Joint Astronomical Colloquium
Michael Meyer
Origins of Stars, Planets, and Life: Early Science with JWST
To arrange a visit with the speaker during the visit, please contact their host: Laura Kreidberg
  17:00 Particle Colloquium
Prof. Dr. Kostas Nikolopoulos
Where does mass come from? Spherical Proportional Counters and other approaches for light Dark Matter searches
Physikalisches Institut INF 226, Konferenzraum 1-3 (Room 00.101 bis 00.103)

Wednesday, 28 May 2025

  09:30 Seminar Dynamik und Struktur von Atomen und Molekülen
Pankaj Seliya; Excited atoms & molecules in strong fields
Two-Dimensional Terahertz-Infrared-Visible Spectroscopy of Molecular C-H groups
Zentraler Seminarraum / Central seminar room (library)
  15:00 Seminar Stored and Cooled Ions
Daniel Lange, CERN/MPIK
ISOLTRAP Advances in Ion Purification: First Application of a Novel Mass-Selective Re-Trapping Technique and Recent Results
Central seminar room, library building
Hybrid seminar: central seminar room, library building + Zoom: Meeting-ID: 915 1204 2752 Passcode: 758933

Friday, 30 May 2025

  17:00 Physikalisches Kolloquium
Prof. Dr. Rudi Grimm
Mixed Quantum Gases: From Cold Collisions to Many-Body Physics in the Ultracold
KIP, INF 227, Hörsaal 1

Ultracold mixtures combine atomic species with fundamentally different properties. Bosons can meet fermions, heavy particles can meet light ones, interparticle interactions can be controlled precisely by external fields, and novel quantum systems emerge with intriguing properties. Over the past 25 years, great progress to prepare various types of mixtures in the laboratory has opened up numerous excited research avenues, related to the few- and many-body physics of atomic and molecular quantum systems.

I will start with a brief review of early experiments carried out in the late 1990’s at the MPI for Nuclear Physics in Heidelberg on mixtures of lithium and cesium. These activities triggered many exciting further developments, including experiments in Heidelberg and Innsbruck on cooling and trapping techniques, thermodynamics, heteronuclear molecules, Efimov quantum states, and on the physics of quasi-particles.

In the main part of my talk, I will focus on the specific topic of quasi-particles called “Fermi polarons”, which we have extensively studied in Innsbruck with potassium atoms (bosonic or fermionic) immersed as impurities in a Fermi sea of lithium atoms. In a series of experiments over the past decade, we have explored the energy spectrum, the formation dynamics, decay and coherence properties, and mediated interactions between polarons. Ongoing experiments are dedicated to the motion of impurities after controlled kicks by photon momentum transfer. Most strikingly, we observe a motion-induced breakdown of the polaron above a critical momentum, where the particle gets “undressed” and becomes a bare particle.


Monday, 2 June 2025

  13:00 DFG Funding Opportunities for PhD researchers and Postdocs
Otto-Hahn-Hörsaal (library building)
Dr. Ina von der Beck and Dr. Margret Heinze Deutsche Forschungsgemeinschaft
The DFG (Deutsche Forschungsgemeinschaft) offers funding opportunities for all career stages between doctorate and professorship. This talk provides a general overview of the DFG funding portfolio for postdocs, with a specific focus on the Walter Benjamin Programme and the Emmy Noether Programme. We will also give advice on proposal submission, explain the review process and are open to your questions. PhD researchers and postdocs of all disciplines are welcome to join!
 
 


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