You are cordially invited to the SCL seminar of the Center for the Study of Complex Systems, which will be held on **Thursday, 24 January 2019 at 14:00** in the library reading room “Dr. Dragan Popović” of the Institute of Physics Belgrade. The talk entitled

Floquet-Engineering of Scattering of Ultracold Atoms and Topological Edge States

will be given by **Christoph Dauer** (Department of Physics, Technical University of Kaiserslautern, Germany).

**Abstract of the talk:**

Recent experimental and theoretical investigations have shown that the time-periodic modulation of a quantum system leads to exotic quantum states, which are inaccessible in thermal equilibrium. The dynamics of such a system is governed by an effective Hamiltonian whose parameters can be tuned by the drive [1].

This talk will be split into two parts. The first is about the scattering of ultracold atoms by a time-periodic interaction potential. After introducing a Floquet-scattering theory for such potentials we report on the major implication, the occurrence of scattering resonances which can be used in order to tune the s-wave scattering length to large positive and negative values. Furthermore, these resonances can be tuned by the parameters of the drive, for example one can tune the resonance width by adjusting the driving strength. The first part is closed with a short explanation on the physical origin of these resonances.

In the second part we will discuss the robustness of a topologically protected edge state under time-periodic driving [2]. We will give a short introduction in our model system, the Su-Schrieffer-Heeger model with periodically modulated hopping amplitudes at the edge and its experimental realisation. The results are explained by using Floquet theory. They show that there exists a Floquet edge mode for certain regimes of the driving frequency, but if edge and bulk are coupled via the drive, the edge state becomes depopulated despite the topological protection. This shows the limitations of the robustness of topologically protected edge modes under the influence of time-periodic driving.

[1] A. Eckardt, Rev. Mod. Phys. 89, 011004 (2017).

[2] Z. Cherpakova, C. Jörg, C. Dauer, et al., arXiv:1807.02312 (2018).