Seminar of Physics of Wrocław University of Technology
PWr, bud. A1, sala 322
How closed quantum systems forget, and when they remember
dr inż. Patrycja Łydżba
Instytut Fizyki Teoretycznej, Politechnika Wrocławska
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.
