Wrocław University of Science and Technology Physics Seminar – Monday 2nd of June 2025

We cordially invite you to Wrocław University of Science and Technology Physics Seminar on Monday 2nd of June 2025 at 11:15 in room 322, building A-1, where there will be delivered a lecture:

How closed quantum systems forget, and when they remember
 
dr inż. Patrycja Łydżba
Institute of Theoretical Physics, Wrocław University of Science and Technology
 
Please find an abstract below.
 
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I discuss the thermalization of closed quantum systems. This refers to their ability to relax toward steady states described by only a few quantities, such as mean energy or particle number. I introduce the eigenstate thermalization hypothesis, which underpins our current understanding of this process. I then present notable exceptions to thermalization, focusing on Hilbert space fragmentation, where the Hamiltonian breaks into exponentially many (in system size) dynamically disconnected blocks. In the final part, I show that a suitably chosen perturbation can induce a gradual merging of these fragmented subspaces. This slow restoration of ergodicity gives rise to an extended critical regime, marked by multiple peaks in the fidelity susceptibility. Each peak signals a change in the number of blocks and corresponds to ultra-slow relaxation of local observables.