## Quantum many-body scars, mixed phase spaces and non-universal thermalization

**Speaker:**Maxim Serbyn, Institute of Science and Technology

**When:**October 11, 2019 (Fri), 12:00PM to 01:00PM (add to my calendar)

**Location:**SCI 352

**Hosted by:**Anatoli Polkovnikov

*This event is part of the Biophysics/Condensed Matter Seminar Series. *

The statistical mechanics 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. For quantum many-body systems, statistical mechanics predicts the equilibration of highly excited non-equilibrium state towards a featureless thermal state. Hence, it is highly desirable to explore possible ways to avoid ergodicity in quantum systems. Many-body localization presents one generic mechanism for a strong violation of ergodicity relying on the presence of quenched disorder. In my talk I will discuss a different mechanism of the weak ergodicity breaking relevant for the experimentally realized Rydberg-atom quantum simulator [1]. This mechanism arises from the presence of special eigenstates in the many-body spectrum that are reminiscent of quantum scars in chaotic non-interacting systems [2], which were recently understood as emerging from the embedded SU(2) symmetric subspace [3]. In this talk I will concentrate on the variational description of unusual quantum many-body revivals that originate from the special eigenstates. I will relate this dynamics to presence of stable periodic trajectories within time-dependent variational principle (TDVP) description of dynamics. I will use TDVP to find new “scars” and explore their response to perturbations of the Hamiltonian. Finally, I will argue that the mixed phase space generally leads to non-universal dependence of thermalization on the initial state and discuss a new opportunities for the creation of novel states with long-lived coherence in systems that are now experimentally realizable [1].

[1] H. Bernien, et al., Nature 551, 579–584 (2017), arXiv:1707.04344 [2] C. J. Turner, A. A. Michailidis, D. A. Abanin, M. Serbyn, Z. Papić, Nature Physics (May 2018), arXiv:1711.03528 and Phys. Rev. B 98, 155134 (2018) arXiv:1806.10933 [3] S. Choi, et al., Phys. Rev. Lett. 122, 220603 (2019) arXiv:1812.05561 [4] A. A. Michailidis, C. J. Turner, Z. Papić, D. A. Abanin, M. Serbyn, arXiv:1905.08564