Projects

Project E1: Quantum-gas microscopy of large-scale bosonic quantum gases J. Zeiher (MPQ Garching) I. Bloch (MPQ Garching)

In this project, we will explore the out-of-equilibrium dynamics of large-scale bosonic quantum gases using a combination of microscopic control and detection. We will address three broad areas, namely many-body localized systems in one and two spatial dimensions, spin transport in large-scale Heisenberg models and constrained dynamics in lattice gases coupled to long-range interacting Rydberg states. We will explore these systems in an experimental quantum simulator featuring a quantum-gas microscope, which allows for single particle sensitive preparation, manipulation, and detection of many-body systems. Touching on the three central objectives of the research unit, we plan to closely collaborate with all theoretical projects.

Figure taken from Choi et al., Science 352, 1547 (2016).

Project E2: Non-ergodic dynamics in tunable Bose-Hubbard models M. Aidelsburger (LMU Munich & MPQ Garching) I. Bloch (LMU Munich)

Within this project, we are going to complete the development and construction of a tunable experimental platform based on the unique properties of ultracold Cs atoms, which combines bichromatic superlattices, state-dependent lattices, Feshbach resonances and quantum-gas microscopy in order to study non-ergodic dynamics beyond conventional many-body localization and standard Bose-Hubbard models. Additionally, we are going to investigate the rich relaxation dynamics of tilted Bose-Hubbard models in one- and two-dimensions. Tilted Hubbard models are expected to perturbatively exhibit fragmentation in the limit of large tilts. One of the most striking signatures of fragmentation is the strong initial-state dependence of the relaxation dynamics, which can be directly observed using quantum gas microscopes.

Figure taken from Impertro et al., arXiv:2212.11974.

Project E3: Quantum-gas mixtures with extreme mass imbalance C. Gross (Eberhard Karls Universität Tübingen)

In this project we aim to study thermalization dynamics and transport in an atomic Bose-Fermi quantum gas mixture with extreme mass imbalance. The imbalance naturally leads to a very pronounced heterogeneity of timescales in the many-body system. Such a scenario has been predicted to show very slow dynamics, peculiar hydrodynamic behavior and quasi-localization. We will study the relaxation dynamics of light fermions initially brought out out equilibrium, which are immersed in a bath of heavy bosons. We will work in close collaboration with the theory partners of the research unit to model and interpret the observed timescales in both settings and to understand the role of kinetic constraints in the system.

Figure from C. Gross.

Project E4: Exploring non-ergodicity in lattice gauge theories with fermionic Yb M. Aidelsburger (LMU Munich & MPQ Garching)

Gauge theories are essential for our understanding of nature and their properties provide exciting new opportunities for interdisciplinary research. Unfortunately, many fundamental properties, especially in the context of out-of-equilibrium dynamics, remain largely inaccessible with conventional numerical methods. Within this project we are going to perform quantum simulation of simplified lattice gauge theories (LGTs) using a new hybrid tweezer-lattice using Yb atoms in state-dependent optical lattices, which will offer high-resolution imaging and manipulation techniques provided by quantum gas microscopy. The main goal is to study non-ergodicity and out-of-equilibrium phenomena in U(1) LGTs coupled to matter. The implementation makes use of the formulation of LGTs in terms of quantum link models (QLMs), where the Hilbert space of the gauge field is truncated and finite.

Figure from M. Aidelsburger.

Project T1: Ergodicity from SYK baths and ergodic inclusions S. Kehrein (Universität Göttingen) M. Heyl (Universität Ausgburg) F. Pollmann (TU Munich)

System plus bath settings have long played an important role in quantum many-body physics. This project addresses two specific such settings that are central to the goals of this research unit:
- Thermalization of isolated ultracold atomic gases can be understood by the system acting as its own quantum bath.
- In many-body localized systems the modeling of ergodic inclusions via a quantum bath can help to analyze the stability of the non-ergodic phase, that is currently hotly debated.
We analyze new models for quantum baths to address these questions. One candidate is the Sachdev-Ye-Kitaev (SYK) model, which has recently generated a lot of excitement in condensed matter physics and in high-energy physics. It has the remarkable properties of being non-integrable and consistent with the eigenstate thermalization hypothesis, while still being analytically solvable. For the modeling of ergodic inclusions we will also investigate Floquet driving and random untary circuits.

Figure from S. Kehrein.

Project T2: Eigenstate thermalization in interacting quantum gases in optical lattices F. Heidrich-Meisner (Universität Göttingen)

Eigenstate thermalization (ETH) provides a very useful concept to predict many aspects of the thermalization dynamics of quantum many-body systems. We will utilize ETH to characterize experimentally relevant systems and aim at connecting ETH with transport properties and measures for quantum chaos based on spectral properties. The project will study interacting Bose gases and mass-imbalanced Fermi gases and uncover the emergence of ETH from the limit of single particles in a sea of a second component to the finite filling case.

Figure taken from Jansen et al., Phys. Rev. B 99, 155130 (2019).

Project T3: Nonergodic dynamics in lattice gauge theories M. Heyl (Universität Ausgburg) M. Carmen Bañuls (MPQ Garching) R. Moessner (MPI PKS Dresden)

This project is at the focal point of several exciting developments in many-body physics, statistical mechanics and non-equilibrium dynamics, both from a conceptual and a technical perspective. It basically addresses the question how local constraints can impede the tendency of many-body systems to thermalise. Using state-of-the-art computational methods, in particular tensor and neural networks, we study lattice gauge theories and kinetically constrained models in order to understand how non-equilibration manifests itself in, e.g., transport properties and dynamical heterogeneities.

Figure taken from Chakraborty et al., arXiv:2203.06198v2.

Project T4: Kinetically constrained dynamics in quantum gases I. Lesanovsky (Eberhard Karls Universität Tübingen) M. Carmen Bañuls (MPQ Garching)

In project T4, we consider so-called kinetically constrained quantum systems that are often formulated in terms of simple dynamical rules, yet can show intriguing collective behavior. In these many-body models, the change of state of a given constituent is conditioned on the current state of its neighborhood. This construction allows to capture many emergent out-of-equilibrium features of classical glassy systems. However, the study of kinetic constraints in quantum systems is still in its infancy. The project's aim is to make progress in this direction by combining advanced numerical methods, such as tensor networks, and large deviation analyses for time-integrated order parameters. We expect that the developed numerical and analytical tools will advance our understanding of dynamical phase transitions in systems that are experimentally realized within our Research Unit.

Figure from Cech et al. (unpublished work).

Project T5: From localization in quenched disorder to new forms of many-body localization F. Pollmann (TU Munich) F. Heidrich-Meisner (Universität Göttingen) R. Moessner (MPI PKS Dresden)

Recent years have seen a great deal of effort to understand whether and how a closed quantum many body system thermalizes. While generic quantum systems are expected to reach a thermal equilibrium as predicted by the Eigenstate Thermalization Hypothesis, several mechanisms challenging this concept have been proposed recently. Notably, many-body localization (MBL) is a candidate for breaking ergodicity and defy thermalization for all eigenstates in the presence of sufficiently. More recently, new mechanisms have been discovered that lead to non-ergodic behavior, including kinetically constrained models (KCMs). In this project we will derive new tools to characterize MBL in disordered systems and investigate the interplay between different ergodicity breaking mechanisms.

Figure taken from Will et al., arXiv:2311.05695.