New non-equilibrium quantum states enabled by breakdown of thermalization
The experimental advances in synthetic quantum systems allow one to probe quantum thermalization and its breakdown. Thermalization occurs in ergodic systems and “erases” quantum information contained in the initial many-body states. Therefore, to create long-lived quantum states, it is of particular interest to find mechanisms of thermalization breakdown. One way of suppressing thermalization is by introducing quenched disorder, which may induce many-body localization (MBL) . Surprisingly, MBL systems may also avoid heating under periodic driving, which opens up the possibility of having stable, Floquet-MBL phases with unusual properties. I will discuss one recent example of such a phase – a two-dimensional Anomalous Floquet Insulator, characterized by fully localized bulk states and chiral, thermalizing edge states . I will discuss another example of a non-trivial Floquet phase – the critical time crystals, which have recently been observed in driven systems of interacting, coherent NV-spins in black diamond. Further, I will argue that MBL may not be the only way to break ergodicity. I will propose another mechanism, “quantum many-body scarring” , which bears a similarity to the well-known phenomenon of quantum scars in few-body chaos, and leads to a weaker form of ergodicity breaking in a many-body system of Rydberg atoms .
 For a review, see D. A. Abanin, E. Altman, I. Bloch, M. Serbyn, arXiv:1804.11065 (2018).
 F. Nathan, D. A. Abanin, E. Berg, N. Lindner, M. Rudner, arXiv:1712.02789 (2018).
 C. Turner, A. Michailidis, D. A. Abanin, M. Serbyn, Z. Papic, Nature Physics (2018) doi:10.1038/s41567-018-0137-5.
 H. Bernien, Nature 551, 579 (2017).
HOST: Mohammad Hafezi