Institut für Theoretische Physik

DFG Research Unit FOR 5522




Research highlight:
Probing quantum many-body dynamics using subsystem Loschmidt echos

The Loschmidt echo generally contains key information about a quantum system, relevant across various scientific fields including quantum chaos, quantum many-body physics, or high-energy physics. However, it is typically exponentially small in system size, posing an outstanding challenge for experiments. Here, we experimentally investigate the subsystem Loschmidt echo, a quasi-local observable that captures key features of the Loschmidt echo while being readily accessible experimentally. Utilizing quantum gas microscopy, we study its short- and long-time dynamics. Performing these measurements in the ergodic regime and in the presence of emergent kinetic constraints, we provide direct experimental evidence for ergodicity breaking due to fragmentation of the Hilbert space. Our results establish the subsystem Loschmidt echo as a novel and powerful tool that allows paradigmatic studies of both non-equilibrium dynamics and equilibrium thermodynamics of quantum many-body systems, applicable to a broad range of quantum simulation and computing platforms.


Joint Experiment-Theory collaboration (Aidelsburger, Bloch, Heyl groups)

Research highlight:
Emergence of constrained dynamics from a Fock-space perspective: Novel insights

Recently, three teams from our research unit arrived at novel insights on the emergence of constrained dynamics from a Fock-space perspective. In two efforts, a mechanism for the formation of dynamically isolated groups of Fock-space nodes was discovered by utilizing known concepts from the theory of localized single-particle excitations in frustrated lattices. This has led to the notion of Fock-space cages [1,2]. For the formation of Fock-space cages, the relevant aspect is the connectivity of nodes in Fock-space. In a third direction [3], the competition of off-diagonal terms and digonal terms in the chosen Fock space basis was also accounted for. To that end, centrality measures from graph theory were generalized to Hamiltonians. For the paradigmatic quantum East model, a clear connection between non-ergodic dynamics and these generalized graph measures could be established.


[1] Jonay, Pollmann, arXiv: 2504.20987
[2] Ben Ami, Heyl, Moessner, arXiv:2504.13086
[3] Menzler, Bañuls, Heidrich-Meisner, arXiv:2504.03458