Institut für Theoretische Physik

15.04.2021

Theoretische Physik

Seminar Statistical Physics

Corneel Casert

Large deviations of kinetically constrained models using recurrent neural networks

Kontakt: Peter Sollich

22.04.2021

Theoretische Physik

Seminar Statistical Physics

Vivien Walter

Application of Machine Learning to decipher lipid phase-related behaviour at the microscopic scale

Kontakt: Peter Sollich

26.04.2021

Theoretische Physik

CMT

Monika Aidelsburger

Zoom link upon request (heidrich-meisner@uni-goetingen.de)

Experimental evidence for Hilbert-space fragmentation in tilted Fermi-Hubbard chains

Well-controlled synthetic quantum systems, such as ultracold atoms in optical lattices, offer intriguing possibilities to study complex many-body problems relevant to a variety of research areas, ranging from condensed matter to high-energy physics. In particular, out-of-equilibrium phenomena constitutenatural applications of quantum simulators, which have already successfully demonstrated simulations in regimes that are beyond reach using state-of-the-art numerical techniques.This enables us to shed newlight on fundamental questions about the thermalization of isolated quantum many-body systems.While generic models are expected to thermalize according to the eigenstate thermalization hypothesis (ETH), violation of ETH is believed to occur mainly in two types of systems: integrable models and many-body localized systems. In between these two extreme limits there is, however, a whole range of models that exhibit more complex dynamics, for instance, due to an emergent fragmentation of the Hilbert space into many dynamically disconnected subspaces. Here, I report on therealization ofthe tilted 1D Fermi-Hubbardmodel which lies at the interface of what is commonly known as Stark-MBL and Hilbert-space fragmentation. We observe a robust memory of the initial state over a wide range of parameters, even down to small values of the tilt [1],and observe strong initial-state dependentthermalization in the large tilt limit -a smoking-gun signature of Hilbert-space fragmentation[2]. [1] S. Scherget al., arXiv:2010.12965 (2020) [2] T. Kohlert et al., in preparation(2021)

Kontakt: Prof. Dr. Fabian Heidrich-Meisner

29.04.2021

Theoretische Physik

Seminar Statistical Physics

Miroslav Hopjan

Characterization of strongly disordered many-body systems from one-particle measures

Kontakt: Peter Sollich

03.05.2021

Theoretische Physik

Quantenfeldtheorie (Forschungsseminar M.Phy.412)

Stefan Kiebacher

Veränderte Zeit!

The Phase Space Distribution of Freeze-In Dark Matter

(Veränderte Zeit!)

Kontakt: K.-H. Rehren

06.05.2021

Theoretische Physik

Seminar Statistical Physics

Maximilian Vossel

Identifying and Understanding Allosteric Hotspots

Kontakt: Peter Sollich

17.05.2021

Theoretische Physik

Aktuelle Probleme der theoretischen Festkörperphysik (Forschungsseminar M.Phy.411)

Leticia Tarruell

Zoom link upon request (heidrich-meisner@uni-goetingen.de)

Realizing a one-dimensional topological gauge theory in an optically dressed Bose-Einstein condensate

Quantum gases constitute a versatile testbed for exploring the behaviour of quantum matter subjected to electric and magnetic fields. While most experiments consider classical gauge fields that act as a simple static background for the atoms, gauge fields appearing in nature are instead quantum dynamical entities that are influenced by the spatial configuration and motion of matter, and that fulfil local symmetry constraints. In my poster, I will discuss our recent realization of a chiral BF theory: a topological gauge theory for linear anyons in the continuum that corresponds to a possible one-dimensional reduction of the Chern-Simons gauge theory effectively describing fractional quantum Hall systems [1,2,3]. By using the local symmetry constraint of the theory, we encode the gauge field in terms of the matter field. The result is a system with chiral interactions, which we engineer in a 39K Bose-Einstein condensate by synthesizing optically dressed atomic states with a momentum-dependent scattering length. When this dependence is linear, matter behaves as if minimally coupled to a density-dependent vector potential. Theoretically, we show that the system then realizes the chiral BF Hamiltonian at the quantum level [4]. Experimentally, we observe its two main features: the formation of chiral bright solitons - self-bound states of the matter field that only exist when propagating in one direction – and the back-action of matter into the gauge field [5]. Our results establish chiral interactions as a novel resource for quantum simulation experiments with ultracold atoms, and pave the way towards investigating linear anyon models [6] and implementing topological gauge theories in higher dimensions [7]. [1] S. J. B. Rabello, Phys. Rev. Lett. 76, 4007 (1996). [2] U. Aglietti, L. Griguolo, R. Jackiw, S.-Y. Pi, and D. Seminara, Phys. Rev. Lett. 77, 4406 (1996). [3] M. J. Edmonds, M. Valiente, G. Juzeliūnas, L. Santos, and P. Öhberg, Phys. Rev. Lett. 110, 085301 (2013). [4] C. S. Chisholm, A. Frölian, E. Neri, R. Ramos, L. Tarruell, and A. Celi, in preparation. [5] A. Frölian, C. S. Chisholm, C. R. Cabrera, E. Neri, R. Ramos, A. Celi, and L. Tarruell, in preparation. [6] M. Bonkhoff, K. Jägering, S. Eggert, A. Pelster, M. Thorwart, and T. Posske, Phys. Rev. Lett. 126, 163201 (2021). [7] G. Valentí-Rojas, N. Westerberg, and P. Öhberg, Phys. Rev. Research 2, 033453 (2020).

Kontakt: Prof. Dr. Fabian Heidrich-Meisner

20.05.2021

Theoretische Physik

Seminar Statistical Physics

Jelger Risselada

Membrane interfacial recognition of viruses and cancer cells

Kontakt: Peter Sollich

27.05.2021

Theoretische Physik

Seminar Statistical Physics

Alireza Soleimani

Ultra Coarse-grained Molecular Dynamics Simulation of Lipid Bilayer Membranes

Kontakt: Peter Sollich

03.06.2021

Theoretische Physik

Seminar Statistical Physics

Dmitrii Makarov

Non-Markovian barrier crossing dynamics from single-molecule measurements

Kontakt: Peter Sollich

07.06.2021

Theoretische Physik

CMT

Prof. Armando A. Aligia

Zoom link upon request (heidrich-meisner@uni-goetingen.de)

New results on the Kondo effect in systems with atoms and molecules on
metallic surfaces

After a brief introduction to the Kondo effect, I will briefly explain the explanations so far that explain the presence of a peak or a dip in the differential conductance dI/dV near V=0 observed by STM. Recently, interpreting experiments for Co on Cu(111), in which an antiresonance in dI/dV at V=0 AND a resonance near the bottom of the conduction band are observed, we conclude by NRG calculations that the STM tip “sees” mainly the Co s electrons and the dip is due to interference effects [1]. This is confirmed by recent ab initio calculations [2]. In addition, from other NRG calculations in a spin-1 two-channel Kondo model with anisotropy D(SZ)2 we find a topological quantum phase transition in which the Kondo peak is suddenly turned to a dip with increasing D [3]. For large D the system is in a “non-Landau” Fermi liquid phase not adiabatically connected to a non-interacting system. Extending the theory to non-equivalent orbitals and non-zero magnetic field we can explain several relevant experiments in Fe phthalocyanine [4].

[1] J. Fernández, P. Roura-Bas, and A. A. Aligia, Phys. Rev. Lett. 126, 046801 (2021) [2] M. S. Tacca et al., arXiv:2103.12560. [3] G. G. Blesio, L. O. Manuel, P. Roura-Bas, and A. A. Aligia, Phys. Rev. B 98, 195435 (2018), Phys. Rev. B 100, 075434 (2019) [4] R. Zitko, G. G. Blesio, L. O. Manuel, and A. A. Aligia, ArXiv:2105.13248

Kontakt: Prof. Dr. Fabian Heidrich-Meisner

10.06.2021

Theoretische Physik

Seminar Statistical Physics

David Hickey

Physics of particle capture by cilia

Kontakt: Peter Sollich

11.06.2021

Theoretische Physik

CMT

Igor Lesanovsky

Zoom link upon request (heidrich-meisner@uni-goetingen.de)

Neural network dynamics in open quantum many-body systems

Open quantum systems composed of atoms interacting with light exhibit behaviour that is akin to that of associative memories [1]. This means that they possess stationary states that can be interpreted as stored memory patterns, which are retrieved when the initial state is inside the basin of attraction of a given pattern [2]. The corresponding pattern retrieval dynamics can be observed in actual experimental settings. In these experiments atoms are confined within an optical cavity whose photons mediate long-range interactions [3]. Stored patterns are encoded in the atom-light coupling constants. This setting offers an interesting opportunity for studying quantum generalisations of associative memories and stored (quantum) patterns in this context [4]. Moreover, it allows to systematically construct scenarios in which quantum effects might be beneficial, e.g., for speeding up the pattern retrieval process [5]. I will talk about recent research of my group on this subject, which builds a bridge between classic machine learning concepts, such as the Hopfield Neural Network, and most recent experimental manifestations of synthetic quantum matter.

[1] E. Fiorelli et al., Physical Review Letters 125, 070604 (2020) [2] F. Carollo and I. Lesanovsky, arXiv:2009.13932 (2020) [3] V.D. Vaidya et al., Physical Review X 8, 011002 (2018) [4] P. Rotondo et al., Journal of Physics A 51, 115301 (2018) [5] E. Fiorelli et al., Physical Review A 99, 032126 (2019)

Kontakt: Prof. Dr. Fabian Heidrich-Meisner

17.06.2021

Theoretische Physik

Seminar Statistical Physics

Etienne Fodor

Active matter under control

Kontakt: Peter Sollich

24.06.2021

Theoretische Physik

Seminar Statistical Physics

Kai Stroh

Quantifying membrane curvature sensing of proteins

Kontakt: Peter Sollich

28.06.2021

Theoretische Physik

Quantenfeldtheorie (Forschungsseminar M.Phy.412)

Bernard Kay

A product picture for quantum electrodynamics

Kontakt: K.-H. Rehren

28.06.2021

Theoretische Physik

CMT

Martin Wenderoth

Zoom link upon request (heidrich-meisner@uni-goetingen.de)

Transport in epitaxial graphene on the nanoscale

The transport properties of epitaxial graphene have been subject of intense theoretical and experimental investigations over the past years. Besides electron-electron and electron-phonon scattering, the charge transport is determined by structural defects such as impurities, substrate steps or monolayer/bilayer junctions. The latter induce spatially varying potential landscape as well as an inhomogeneous current density. Scanning Tunneling Microscopy combined with a potentiometric extension called Scanning Tunneling Potentiometry (STP) has opened a way to study these transport properties down to the nanometer scale. Using an STP setup based on a home-built low-temperature STM operating down to 6 K and applicable magnetic field of up to 6T, we have investigated the sheet resistance of graphene on the local scale and have analyzed charge transport across different localized defects on a sub-nanometer scale.

Kontakt: Prof. Dr. Fabian Heidrich-Meisner

01.07.2021

Theoretische Physik

Seminar Statistical Physics

Cai Dieball

Understanding empirical densities and currents in continuous space

Kontakt: Peter Sollich

05.07.2021

Theoretische Physik

Quantenfeldtheorie (Forschungsseminar M.Phy.412)

Karl-Henning Rehren

The dressed model: a step towards off-shell QED

The "dressed model" is a nonperturbative exactly solvable model to grasp the pertinent infrared properties of QED without including the full interaction. In contrast to the well-known successful (BRST or Gupta-Bleuler) techniques for computing the S-matrix, it constructs the charged fields on a Hilbert space from the outset. Its particle states are infraparticles, and uncountably many superselection sectors appear manifestly.

Kontakt: K.-H. Rehren

08.07.2021

Theoretische Physik

Seminar Statistical Physics

Vitali Telezki

Dynamical structure formation of dipolar swimmers in (time dependent) external magne

Kontakt: Peter Sollich

09.07.2021

Theoretische Physik

CMT

Manuel Weber

Zoom link upon request (heidrich-meisner@uni-goetingen.de)

Nonequilibrium dynamics of field-driven electron-phonon systems in the adiabatic limit

Electron-phonon interactions play an important role in strongly-correlated materials driven out of equilibrium. However, numerical simulation of microscopic models is often restricted to small system sizes due to the unbound bosonic Hilbert space or requires approximate schemes (such as perturbation theory). Here we show that the nonequilibrium dynamics of electron-phonon models in a time-dependent electromagnetic field can be calculated efficiently in the adiabatic limit of zero phonon frequency using a Monte Carlo method. We apply our method to the one-dimensional Holstein model driven by a strong dc electric field. Instead of heating up towards a featureless infinite-temperature state, the system develops minibands with nontrivial distribution functions that can be tuned between positive, negative, or close-to-infinite effective temperatures. We show that the current is prematurely driven to zero as the system reaches an even distribution of electrons in momentum space. Our results suggest that nontrivial metastable distribution functions could be realized in the prethermal regime of quantum systems coupled to slow bosonic modes.

Kontakt: Prof. Dr. Fabian Heidrich-Meisner

14.07.2021

Theoretische Physik

Quantenfeldtheorie (Forschungsseminar M.Phy.412)

Rishabh Jha

Continuation through the Big Bang Singularity

General relativity admits singular solutions, where the predictability of evolution of physical degrees of freedom is expected to break down. This notion is challenged by presenting classical solutions that satisfy existence and uniqueness theorems of differential equations at the big bang singularity, thereby surviving through it. This is presented for the class of homogeneous anisotropic cosmological models, namely the Bianchi IX universe, coupled to stiff matter sources such as scalar fields, using the ADM formalism of general relativity. The talk focuses on developing the prerequisites for this work, in particular the 3+1 decomposition of spacetime (& consequently the ADM formalism) as well as an introduction to the homogeneous universes. The talk will conclude by showing the results for the case of a scalar field minimally coupled to gravity whose classical solutions survive through the big bang singularity. Possible future directions will be mentioned.

Kontakt: K.-H. Rehren

15.07.2021

Theoretische Physik

Seminar Statistical Physics

David Hartich

Thermodynamic Uncertainty Relation Bounds the Extent of Anomalous Diffusion

Kontakt: Peter Sollich

03.09.2021

Theoretische Physik

CMT

Yiting Zhang

Spectra of Laplacian matrix for one- and two-dimensional lattice with random nearest-neighbour-couplings

Kontakt: Prof. Dr. Fabian Heidrich-Meisner

03.09.2021

Theoretische Physik

CMT

Rafal Swietek

Zoom link upon request (heidrich-meisner@uni-goetingen.de)

Thermodynamics in the generalized Kondo-Heisenberg model

Kontakt: Prof. Dr. Fabian Heidrich-Meisner

03.09.2021

Theoretische Physik

CMT

Soeren Wilkening

Zoom link upon request (heidrich-meisner@uni-goetingen.de)

DMRG-LBO method for inhomogeneous one-dimensional electron-phonon systems

Kontakt: Prof. Dr. Fabian Heidrich-Meisner

10.09.2021

Theoretische Physik

CMT

Arturo Pérez Romero

Zoom link upon request (heidrich-meisner@uni-goetingen.de)

"Extended three-color Fermi Hubbard"

Kontakt: Prof. Dr. Fabian Heidrich-Meisner

23.09.2021

Theoretische Physik

Seminar Statistical Physics

Johannes Fiedler

Macroscopic impacts of the quantum vacuum —
from matter-wave interference to quantum sensing

Join Zoom Meeting https://uni-goettingen.zoom.us/j/5324796455?pwd=WEZGZWRTMWJKcXU0bmFUVTVXMllSdz09

Kontakt: Matthias Krüger