Singular Floquet scattering with atomic interactions

The shaping of physical systems by periodic driving is a powerful tool gaining increasing attention. However the modelling of periodically modulated nonperturbative effects is challenging due to the necessity of employing... [ view full abstract ]

The shaping of physical systems by periodic driving is a powerful tool gaining increasing attention. However the modelling of periodically modulated nonperturbative effects is challenging due to the necessity of employing time-dependent tools beyond perturbation theory, and often reduces to a time-independent approximation with effective parameters. It is hence an important question to determine the extent of the validity of such effective descriptions, and possible directions going beyond it.

I will present a nonperturbative and time-dependent approach to Floquet two-body atomic interactions [1]. With it we find the existence of singular solutions that cannot be seen in a time-independent approximation, where poles of the scattering S-matrix cross the real energy axis at a critical drive strength. This makes the S-matrix nonanalytic at singular points, similar to "spectral singularities" (or "exceptional points"). For the corresponding quasi-bound states that can tunnel out of (or get captured within) a potential well, this results in a discontinuous jump in both the angular momentum and energy of emitted (absorbed) waves. We also analyze elastic and inelastic scattering of slow particles in the time-dependent potential. For a drive amplitude at the singular point, there is a total absorption of incoming low energy (s-wave) particles and their conversion to high energy outgoing (mostly p-) waves.

In particular, I will discuss the application and observability of these singularities with ultracold atoms and ion-atom hybrid systems [2,3].

[1] H. Landa, Phys. Rev. A 97, 042705 (2018).
[2] H. Landa, in preparation.
[3] A. Sykes, H. Landa, and D. Petrov, PRA 95, 062705 (2017).