The thermodynamic description of many-particle systems rests on the assumption of ergodicity, the ability of a system to explore all allowed configurations in the phase space. Recent studies on many-body localization have revealed the existence of systems that strongly violate ergodicity in the presence of quenched disorder. Here, we demonstrate that ergodicity can be weakly broken by a different mechanism, arising from the presence of special eigenstates in the many-body spectrum that are reminiscent of quantum scars in chaotic non-interacting systems.
In this talk, I will first give a brief introduction to the Rydberg atom experiment setup and the effective Hamiltonian (PXP model), which is the first known model exhibiting quantum many-body scar. Next, I will introduce some basics of quantum thermalization and the eigenstate thermalization hypothesis. Then, I will return to the PXP model, explaining the underlying mechanism for its non-thermal evolution.
 Bernien, H., Schwartz, S., Keesling, A. et al. Probing many-body dynamics on a 51-atom quantum simulator. Nature 551, 579–584 (2017).
 Turner, C.J., Michailidis, A.A., Abanin, D.A. et al. Weak ergodicity breaking from quantum many-body scars. Nature Phys 14, 745–749 (2018).
 Joshua M Deutsch, Eigenstate thermalization hypothesis. Rep. Prog. Phys. 81 (2018).
 C. J. Turner, A. A. Michailidis, D. A. Abanin, M. Serbyn, and Z. Papić, Quantum scarred eigenstates in a Rydberg atom chain: Entanglement, breakdown of thermalization, and stability to perturbations. Phys. Rev. B 98, 155134 (2018).