Institute for Theoretical Physics

21/10/24

Theoretische Physik

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

Kontakt: St. Kehrein, F. Heidrich-Meisner

24/10/24

Theoretische Physik

CMT

Thierry Gimarchi

Hall effect in quasi-1D interacting systems

Hall effect is one of the most central measures in condensed matter systems. In the most naïve semi-classical theories, it gives access to the number of carriers. We know however that this vision is way too simple and for non-interacting systems the Hall effect has been beautifully connected to the curvature of the Fermi surface and to topological invariants. However, and despite severe efforts, understanding the Hall effect for interacting systems remain an ongoing challenge. I will show in this talk how one can compute the Hall effect for coupled 1D structures such as ladders, and how using numerical approaches one can predict at large tunnelling between the legs of the latter or large interactions a universal behavior of the Hall coefficient for an interacting ladder [1]. This prediction will be successfully compared with recent experiments in systems with synthetic gauge fields and synthetic dimensions [2]. I will also discuss how in the opposite limit of small tunnelling, field theory methods such as bosonisation allow to compute the Hall coefficient and related it to the charge stiffness of the system in the absence of a magnetic field [3].

[1] S. Greschner, M. Filippone, T. Giamarchi, Phys. Rev. Lett. 122, 083402 (2019). [2] T.-W. Zhou, G. Cappellini, D. Tusi, L. Franchi, J. Parravicini, C. Repellin, S. Greschner, M. Inguscio, T. Giamarchi, M. Filippone, J. Catani, L. Fallani, Science 381, 427 (2023). [3] R. Citro, T. Giamarchi, E. Orignac, arXiv:2404.16973 (2024).

Kontakt: Prof. Dr. Fabian Heidrich-Meisner

24/10/24

Theoretische Physik

Seminar Statistical Physics

Daniele Gamba

Hyperballistic transport in dense ionized matter under external AC electric fields

Kontakt: Peter Sollich

04/11/24

Theoretische Physik

CMT

Roger Melko

Language Models for Quantum Simulation

As the frontiers of artificial intelligence advance more rapidly than ever before, generative language models like GPT are already causing significant economic and social transformation. In addition to their remarkable performance on typical language tasks - such as generating text from a prompt - language models are being rapidly adopted as powerful ansatze states for quantum many-body systems. In this talk, I will discuss the use of language models for learning states realized in today's experimental quantum simulators. By combining variational optimization with data-driven learning using qubit projective measurements, I will show how language models are poised to become one of the most powerful computational tools in our arsenal for the design and characterization of quantum simulators and fault-tolerant computers.

Kontakt: Prof. Dr. Heidrich-Meisner

07/11/24

Theoretische Physik

Seminar Statistical Physics

Rick Bebon

Path-based statistical mechanics from the perspective of measure concentration

Kontakt: Peter Sollich

07/11/24

Theoretische Physik

Seminar Statistical Physics

Kontakt: Peter Sollich

08/11/24

Theoretische Physik

CMT

Chiara Paletta

Integrability of open^2 quantum circuits

Integrable unitary circuits can be seen as a Trotter formulation of certain integrable continuous-time Hamiltonians. Their importance lies in the potential to use analytical methods to compute physical observables, such as correlation functions and mean particle current. In this talk, I will explain the different terms in the title and explore their connections. I will begin with an introduction to integrability, which is the property of a physical system having an infinite number of commuting conserved charges. Then, I will discuss the discrete dynamical evolution of a quantum system and explain how a quantum circuit can be integrable. Using this construction, I will build different quantum circuits with open boundary conditions and address the question of under which conditions the structure of the boundary gate factorizes. In continuous-time evolution, this question corresponds to understanding when we can interpret the boundary terms as a Lindbladian: the effective action of a Markovian environment on the system. I will show how, for specific parameter choices, these solutions correspond to Lindbladians that inject or remove particles at the boundaries of the spin chain. Based on arXiv:2406.12695 with T. Prosen.

Kontakt: Prof. Dr. Fabian Heidrich-Meisner

14/11/24

Theoretische Physik

Seminar Statistical Physics

Jakob Metson

Escaping Kinetic Traps Using Non-Reciprocal Interactions

Kontakt: Peter Sollich

21/11/24

Theoretische Physik

Seminar Statistical Physics

Daniele Gamba

Hyperballistic transport in dense ionized matter under external

Kontakt: Peter Sollich

22/11/24

Theoretische Physik

CMT

Ulrich Schneider

Ultracold atoms in unconventional lattices: geometric frustration, flat bands, and localization

Ultracold atoms in optical lattices are one of the major platforms for quantum simulations and many-body physics. Their versatile nature and high controllability enable the realization of novel quantum phases, the study of phase transitions, and the observation of non-equilibrium dynamics. In the past, most experiments studied these phenomena in the simplest lattice geometries, namely the primitive 1D lattice, the square lattice, and the cubic lattice. In this talk, we look at many-body physics in 2D in different lattice geometries. These range from the triangular lattice, where geometric frustration can give rise to chiral superfluids, over the Kagome lattice, where it gives rise to a flat band, to optical quasicrystals, where the notion of band-structure is not even directly applicable. In all cases I will present experimental results and highlight open questions.

Kontakt: Prof. Dr. Fabian Heidrich-Meisner

28/11/24

Theoretische Physik

Seminar Statistical Physics

Mike Chatzitoffi

Thermodynamic inference of correlations in non equilibrium collective dynamics

Kontakt: Peter Sollich

03/12/24

Theoretische Physik

Theoretisch-physikalisches Seminar - Dienstag

Volker Meden

PT-symmetric, non-Hermitian quantum many-body theory

Parity-time-(PT-)symmetric, non-Hermitian quantum many-body systems are realized as open quantum systems with PT symmetry and compatible couplings to the environment. I review the methodology to theoretically investigate such systems. Taking a mathematical physics perspective, the corresponding Hamiltonians are studied on one hand using the formalisms of PT-symmetric and biorthogonal quantum mechanics, both of which are strongly related. In these frameworks, the notion of observables is altered compared to the standard formalism of Hermitian quantum mechanics. Furthermore, the inner product is modified by including a metric operator. On the other hand, the formalism of Hermitian quantum mechanics is employed. Considering several models ranging from a toy model to one exhibiting quantum critical behavior, I show that the standard formalism always leads to reasonable results while PT-symmetric and biorthogonal quantum mechanics produces results that cannot be reconciled with our physical intuition. The ancilla approach provides a justification for using the standard formalism independent of any specific models. I discuss that within the standard formalism useful methods of quantum many-body theory such as linear response theory and functional integrals cannot easily be extended to non-Hermitian systems. Ironically, this is straightforward within PT-symmetric and biorthogonal quantum mechanics.

Kontakt: Theoretische Physik, Prof. Dr. Fabian Heidrich-Meisner

05/12/24

Theoretische Physik

Seminar Statistical Physics

Laya Parkavousi

Enhanced stability in multi-species non-reciprocal mixtures

Kontakt: Peter Sollich

12/12/24

Theoretische Physik

Seminar Statistical Physics

Jeferson Dias

Spectral density and localization transition of heterogeneous random graphs

Kontakt: Peter Sollich

12/12/24

Theoretische Physik

Seminar Statistical Physics

Marcus Müller

A tutorial on polymer rheology

Kontakt: Peter Sollich

16/12/24

Theoretische Physik

Quantenfeldtheorie (Forschungsseminar M.Phy.412)

Daniel Reichelt

The Alaric parton shower

Kontakt: Steffen Schumann

09/01/25

Theoretische Physik

Seminar Statistical Physics

Heiko Menzler

tba

Kontakt: Peter Sollich

23/01/25

Theoretische Physik

Seminar Statistical Physics

Martin Johnsrud

Generalized Fluctuation Dissipation Relations for Active Field Theories

Kontakt: Peter Sollich

06/02/25

Theoretische Physik

Seminar Statistical Physics

Luca Cocconi

tba

Kontakt: Peter Sollich