Talks

coffee, tea, cookies at 16:00 in the main hall
Monday 16:30-17:30
Seminar room 1+2
- monthly seminars -
Seminar room 4
- weekly seminars -
Monday 11:00-12:00
Seminar room 4
Wednesday 16:30 - 17:30
Seminar room 1D1
Thursday 14:00-15:00
Seminar room 4

 

 

Talks in chronological order

24 Jun 2024
04:30 PM

Colloquium

Seminarroom 1+2+3
26 Jun 2024
02:00 PM

Mechanics of Hydra regeneration and the role of topological defects

Yonit Maroudas-Sacks (MPI-CBG/TUD-PoL)

Hydra is a classic model system for morphogenesis thanks to its simple body plan and its ability to regenerate an entire animal from small tissue pieces. We use regenerating Hydra as a flexible platform to explore how mechanical forces and feedback contribute to the formation and stabilisation of the body plan during morphogenesis. We have previously shown that the nematic organisation of the supra-cellular muscle fibres in regenerating Hydra defines a coarse-grained field, whose dynamics provide an effective description of the morphogenesis process. Topological defects in the nematic order, which emerge early in the regeneration process, identify the sites where morphological features develop. Here we show that the future head region in regenerating tissue fragments, which contains an aster-shaped topological defect in the fibre organisation, undergoes multiple extensive stretching and rupture events from the onset of regeneration. These recurring localised tissue deformations arise due to transient contractions of the muscle fibres that focus mechanical strain at defect sites. We propose a closed-loop feedback mechanism promoting head organiser formation, and develop a biophysical model of regenerating Hydra tissues that incorporates a morphogen source activated by mechanical strain and an alignment interaction directing fibres along morphogen gradients. We further explore the effect of geometrical confinement on the morphological outcome during Hydra regeneration. We find that confinement can be used to create frustrating conditions that result in regeneration with multiple body-axes, and relate this to the fibre organisation and presence of ‘excess’ defects. Overall our results suggest that the nematic organisation of the muscle fibres can be considered a “mechanical morphogen” whose dynamics and active-force generation, in conjugation with additional biochemical and biophysical processes, underlies the remarkable self-organisation into functional animals during Hydra regeneration. Note that this work was also just published on biorxiv: 1) https://www.biorxiv.org/content/10.1101/2024.06.13.598802v1 2) https://www.biorxiv.org/content/10.1101/2024.06.13.598813v1

Seminarroom 4 iCal Event
27 Jun 2024
04:30 PM

QDS: Controlling and imaging ultrafast quantum dynamics using tailored laser fields

Dr. Matthias Kübel (Friedrich Schiller University, Jena)

The ability to precisely control the properties of femtosecond laser pulses allows one to tailor the electric field evolution to the needs of a specific measurement task. With such versatile tool, quantum dynamics in atoms and molecules, enfolding on the (sub-) femtosecond time scale, can be observed and even manipulated experimentally. In my talk, I will introduce a streak camera for photoionization in an intense laser field, called STIER (Sub-cycle Tracing of Ionization Enabled by infra-Red). I will discuss experiments in which STIER is used to track ionization dynamics in a few-cycle laser pulse [1,2], manipulate molecular dissociation [3] and image bound electron wave packets [4]. Finally, I will describe recent results on correlated electron-nuclear dynamics [5] and present progress towards complete molecular movies in which light-induced nuclear and electronic dynamics in small molecules will be imaged simultaneously. References [1] M. Kübel, Z. Dube, A. Y. Naumov, M. Spanner, G. G. Paulus, M. F. Kling, D. M. Villeneuve, P. B. Corkum, and A. Staudte, Phys. Rev. Lett. 119, 183201 (2017). [2] M. Kübel, G. P. Katsoulis, Z. Dube, A. Y. Naumov, D. M. Villeneuve, P. B. Corkum, A. Staudte, and A. Emmanouilidou, Phys. Rev. A 100, 43410 (2019) [3] M. Kübel, M. Spanner, Z. Dube, A. Y. Naumov, S. Chelkowski, A. D. Bandrauk, M. J. J. Vrakking, P. B. Corkum, D. M. Villeneuve, and A. Staudte, Nat. Commun. 11, 2596 (2020). [4] M. Kübel, Z. Dube, A. Y. Naumov, D. M. Villeneuve, P. B. Corkum, and A. Staudte, Nat. Commun. 10, 1 (2019). [5] S. Hell, et al., in preparation (2024)

Room 1D1 iCal Event
28 Jun 2024
05:00 PM

CondMat for Dummies: tba

Attila Szabo (MPI-PKS)

Seminarroom 4 iCal Event
01 Jul 2024
04:30 PM

t.b.a.

Prof. Erwin Frey (LMU Munich)

Seminarroom 1+2+3 iCal Event
03 Jul 2024
02:00 PM

Title t. b. a.

Robert Großmann (University of Potsdam)

Seminarroom 4 iCal Event
04 Jul 2024
04:30 PM

QDS: Building a hierarchy of methods for nonadiabatic molecular dynamics based on the multiple-spawning framework

Dr. Basile Curchod (University of Bristol, UK)

Different theoretical strategies have been developed to simulate the photochemistry of molecules in their full dimensionality, incorporating nonadiabatic (non-Born-Oppenheimer) effects. Two examples of such methods include ab initio multiple spawning (AIMS) and trajectory surface hopping (TSH). AIMS describes the dynamics of nuclear wavepackets using adaptive linear combinations of traveling frozen Gaussians. TSH portrays the nuclear dynamics with a swarm of independent classical trajectories that can hop between potential energy surfaces. In this talk, I intend to survey some of our recent work on developing a hierarchy of methods for excited-state dynamics based on the AIMS framework. I will also spotlight challenges in the field of nonadiabatic molecular dynamics that were identified when simulating time-resolved experimental observables.

Room 1D1 iCal Event
15 Jul 2024
04:30 PM

Boundaries, Inclusions, and Disorder in Active Matter

Prof. Mehran Kardar (Massachusetts Institute of Technology)

Active systems are driven out of equilibrium by exchanging energy and momentum with their environment. This endows them with anomalous mechanical properties which leads to rich phenomena when active fluids are in contact with boundaries, inclusions, or disordered potentials. Indeed, studies of the mechanical pressure of active fluids and of the dynamics of passive tracers have shown that active systems impact their environment in non-trivial ways, for example, by propelling and rotating anisotropic inclusions. Conversely, the long-ranged density and current modulations induced by localized obstacles show how the environment can have a far-reaching impact on active fluids. This is best exemplified by the propensity of bulk and boundary disorder to destroy bulk phase separation in active matter, showing active systems to be much more sensitive to their surroundings than passive ones.

Seminarroom 1+2+3 iCal Event
25 Jul 2024
04:30 PM

QDS: Can quantum computing enhance machine learning and, if yes, how?

Prof. Dr. Romas Krems (The University of British Columbia (Vancouver))

I will begin by demonstrating that the answer to the first question in the title is yes [1], in principle. I will then discuss if the quantum advantage of quantum machine learning can be exploited in practice. To discuss how to build optimal quantum machine learning models, I will describe our recent work [2-3] on applications of classical Bayesian machine learning for quantum predictions by extrapolation. In particular, I will show that machine learning models can be designed to learn from observables in one quantum phase and make predictions of phase transitions as well as system properties in other phases. I will also show that machine learning models can be designed to learn from data in a lower-dimensional Hilbert space to make predictions for quantum systems living in higher-dimensional Hilbert spaces. I will then demonstrate that the same Bayesian algorithm can be extended to design gate sequences of a quantum computer that produce performant quantum kernels for data-starved classification tasks [4]. [1] J. Jäger and R. V. Krems, Universal expressiveness of variational quantum classifiers and quantum kernels for support vector machines, Nature Communications 14, 576 (2023) [2] R. A. Vargas-Hernandez, J. Sous, M. Berciu, and R. V. Krems, Extrapolating quantum observables with machine learning: Inferring multiple phase transitions from properties of a single phase, Physical Review Letters 121, 255702 (2018) [3] P. Kairon, J. Sous, M. Berciu and R. V. Krems, Extrapolation of polaron properties to low phonon frequencies by Bayesian machine learning, Phys. Rev. B 109, 144523 (2024). [4] E. Torabian and R. V. Krems, Compositional optimization of quantum circuits for quantum kernels of support vector machines, Physical Review Research 5, 013211 (2023)

Room 1D1 iCal Event
14 Aug 2024
03:30 PM

IMPRS Seminar

tba (tba)

Seminarroom 4 iCal Event
14 Aug 2024
04:45 PM

IMPRS Seminar

Jan Postulka (UCT Prague)

Seminarroom 4 iCal Event
19 Aug 2024
04:30 PM

Colloquium

Seminarroom 1+2+3 iCal Event
09 Sep 2024
04:30 PM

Colloquium

Seminarroom 1+2+3 iCal Event
16 Sep 2024
04:30 PM

Colloquium

Seminarroom 1+2+3 iCal Event
23 Sep 2024
04:30 PM

Copernicus Revisited: Is the Earth Special?

Prof. Laura Kreidberg (Max Planck Institute for Astronomy)

Nearly 500 years ago, Nicolas Copernicus published his disruptive theory that Earth is not the center of the universe. This "Copernican demotion" has held fast over the centuries, as astronomers have learned that there is nothing particularly remarkable about Earth or even the Milky Way. In the last two decades, however, a new test of the Copernican Principle has emerged -- the discovery of an abundance of planets orbiting other stars. These discoveries allow us to put Earth in context and evaluate whether the formation, architecture, and present-day characteristics of our Solar System are in fact typical. One of the biggest open questions is whether Earth-like exoplanets have water, a key ingredient for life. Thanks to the revolutionary new observing capabilities of the James Webb Space Telescope (JWST), it is possible to characterize the atmospheres of Earth-sized worlds for the first time. In this talk, I will share the latest observations of rocky exoplanet atmospheres from JWST, discuss the implications for their water abundances in comparison to the Earth, and answer the question: was Copernicus wrong?

Seminarroom 1+2+3 iCal Event