06.10.2026 Sebastian Paeckel (LMU Munich)
Location: HIT E 41.1, Time: 12:00
Unlocking Low-Energy Many-Body Spectra with Dynamic Krylov Frames
The recent years have seen enormous experimental progress in designing and controlling strongly correlated quantum materials. At the same time, this progress poses new challenges for theoretical and numerical methods. A particularly pressing problem is the efficient computation of low-energy spectra in strongly correlated systems beyond one spatial dimension.
In this talk, I will introduce dynamic non-unitary Krylov frames as a new framework for addressing this challenge. Building on the recent success of complex-time methods, dynamic non-unitary Krylov frames provide a unifying theoretical framework and a foundation for developing highly efficient numerical approaches to many-body spectral problems.
As an example, I will consider two-hole bound states in the two-dimensional t-J model. I will show how exploiting the structure of dynamic non-unitary Krylov frames enables resolutions at low energies that are inaccessible with conventional approaches. These results demonstrate how the framework can bridge the gap between effective microscopic theories and experimentally relevant energy scales, opening new perspectives for understanding pairing mechanisms in unconventional superconductors.
13.10.2026 Thea Budde (ETH Zurich)
Location: HIT E 41.1, Time: 12:00
Ergodicity breaking from unconventional lattice symmetry
Statistical physics rests on the assumption that many-body systems uniformly explore all available states. The model is only constrained by its symmetries, which are sufficient to predict its long-time behavior. This raises the question of what counts as a symmetry. Traditional notions of symmetry rely on quantities with a straightforward analog in relativistic continuum theories. However, there are broader classes of conserved quantities on the lattice for which this is not the case, such as subsystem symmetries and partial isometries. These can explain why several models seem to break ergodicity and fail to thermalize as was expected when only traditional symmetries are considered. In this talk, I will present examples of models with quantum many-body scars and Hilbert space fragmentation, whose behavior was previously classified as ergodicity breaking, but can instead be explained by unconventional symmetries. These results raise two questions: does all ergodicity breaking originate in unconventional conserved quantities, and what would be a useful classification of lattice conserved quantities in this context?