New non-equilibrium quantum states enabled by breakdown of thermalization

Dmitry Abanin (University of Geneva)

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) [1]. Surprisingly, MBL systems may also avoid heating under periodic driving, which opens up the possibility of having stable, Floquet-MBL phases with unusual properties. One recent example of such a phase is a two-dimensional Anomalous Floquet Insulator, characterized by fully localized bulk states and chiral, thermalizing edge states [2]. I will discuss another, very different example of a non-trivial Floquet phase – a critical time crystal, which has recently been observed in driven systems of interacting, coherent NV-spins in black diamond [3]. Further, I will argue that MBL may not be the only way to break ergodicity. I will propose another mechanism, “quantum many-body scarring” [4], 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 [5].

[1] For a review, see D. A. Abanin, E. Altman, I. Bloch, M. Serbyn, arXiv:1804.11065 (2018)

[2] F. Nathan, D. A. Abanin, E. Berg, N. Lindner, M. Rudner, arXiv:1712.02789 (2018)      

[3] J. Choi et al., arXiv:1806.10169 (2018)

[4] C. Turner, A. Michailidis, D. A. Abanin, M. Serbyn, Z. Papic, Nature Physics (2018) doi:10.1038/s41567-018-0137-5.

[5] H. Bernien et al., Nature 551, 579 (2017).