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DFG Research Unit FOR 5522
Welcome to FOR 5522!
Our team from seven Germany-based research institutions and international research partners investigates nonequilibrium dynamics of closed quantum systems with ultra-cold atoms and state-of-the-art theory.
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PhD School on Nonergodic Quantum Dynamics
In September 2024, our RU will run an international PhD school covering timely topics from the nonequilibrium physics of closed quantum systems. Please visit the webpage for list of lecturers, topics & registration.
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Kick-Off-Meeting Lecture
Frank Pollmann
(TU Munich)
Many-body localization & Constrained Dynamics
Quantum Gas Laboratory Tübingen
Research highlight:
Emergence of fluctuating hydrodynamics in chaotic quantum systems
A fundamental principle of chaotic quantum dynamics is that local subsystems eventually approach a thermal equilibrium state. Large subsystems thermalize slower: their approach to equilibrium is limited by the hydrodynamic build-up of large-scale fluctuations. For classical out-ofequilibrium systems, the framework of macroscopic fluctuation theory (MFT) was recently developed to model the hydrodynamics of fluctuations. We perform large-scale quantum simulations that monitor the full counting statistics of particle-number fluctuations in hard-core boson ladders, contrasting systems with ballistic and chaotic dynamics. We find excellent agreement between our results and MFT predictions, which allows us to accurately extract diffusion constants from fluctuation growth. Our results suggest that large-scale fluctuations of isolated quantum systems display emergent hydrodynamic behavior, expanding the applicability of MFT to the quantum regime.
Group: I. Bloch, M. Aidelsburger (LMU Munich)
Research highlight:
Observation of Hilbert-space fragmentation and fractonic excitations in
two-dimensional Hubbard systems
The relaxation behaviour of isolated quantum systems taken out of equilibrium is among the most intriguing questions in many-body physics. Quantum systems out of equilibrium typically relax to thermal equilibrium states by scrambling local information and building up entanglement entropy. However, kinetic constraints in the Hamiltonian can lead to a breakdown of this fundamental paradigm due to a fragmentation of the underlying Hilbert space into dynamically decoupled subsectors in which thermalisation can be strongly suppressed. Here, we experimentally observe Hilbert space fragmentation (HSF) in a two-dimensional tilted Bose-Hubbard model. Our results mark the first observation of HSF beyond one dimension, as well as the concomitant direct observation of fractons, and pave the way for in-depth studies of microscopic transport phenomena in constrained systems.
Joint Experiment-Theory collaboration (Bloch, Moessner, Pollmann, Zeiher groups)