On frustrated 2d Heisenberg magnets and On the geometric theory of the dynamics of quasi-periodically driven quantum systems

by Chengzhi Le (EPFL)

Wednesday 6 May 2026, 11:00 → 12:00 Europe/Zurich

WHGA/121

Quantum spin models on 2D frustrated lattices can exhibit various phases emerging from zero-point fluctuations. Important examples include Néel order, spin liquids, and valence-bond states. In the first part of the talk, I will briefly present our ongoing study at EPFL of phase transitions in the J_1-J_2 spin-1/2 Heisenberg model on the honeycomb lattice, based on the CTMRG method.

In the second part, the focus shifts from ground states of many-body systems to the dynamics of few-body systems. For periodically driven quantum systems, Floquet theory shows that the evolution can be decomposed into a periodic micromotion and a secular macromotion. A recent study at MPIPKS further showed that Floquet theory can be interpreted geometrically in terms of parallel transport and quantum geometry. I will briefly introduce this geometric Floquet theory in the second part of the talk. Then, I will present in detail our current results on its generalization, the geometric theory on the dynamics of quasi-periodically driven quantum systems, together with the underlying physics.”