Parametric instabilities in a 2D periodically-driven bosonic system: Beyond the weakly-interacting regime

TL;DR

This study experimentally explores how parametric instabilities cause heating and decay of Bose-Einstein condensates in 2D optical lattices under various periodic drives, revealing the dominant role of unstable Bogoliubov modes and the impact of drive geometry and amplitude.

Contribution

It provides the first experimental analysis of parametric instabilities beyond the weakly-interacting regime in 2D driven bosonic systems, highlighting the influence of drive shape and interaction strength.

Findings

Unstable Bogoliubov modes dominate BEC decay.

Heating rates increase with drive amplitude and complexity.

Circular drives induce faster heating than diagonal drives.

Abstract

We experimentally investigate the effects of parametric instabilities on the short-time heating process of periodically-driven bosons in 2D optical lattices with a continuous transverse (tube) degree of freedom. We analyze three types of periodic drives: (i) linear along the x-lattice direction only, (ii) linear along the lattice diagonal, and (iii) circular in the lattice plane. In all cases, we demonstrate that the BEC decay is dominated by the emergence of unstable Bogoliubov modes, rather than scattering in higher Floquet bands, in agreement with recent theoretical predictions. The observed BEC depletion rates are much higher when shaking both along x and y directions, as opposed to only x or only y. This is understood as originating from the interaction-induced non-separability along the two lattice directions. We also report an explosion of the heating rates at large drive amplitudes, and suggest a phenomenological description beyond Bogoliubov theory. In this strongly-coupled regime, circular drives heat faster than diagonal drives, which illustrates the non-trivial dependence of the heating on the choice of drive.