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Parametric instabilities beyond Bogoliubov theory in two-dimensional periodically driven bosonic systems



James V. Porto


We experimentally investigate the effect 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, which allows to break time-reversal symmetry, a prerequisite for realizing topological states of matter. 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 rates are much higher when shaking both along $x$ and $y$, as opposed to only $x$ or only $y$. This is understood as originating from the interaction-induced non-separability of the two directions. We also report an explosion of the heating rates at large drive amplitudes, and suggest a simple beyond Bogoliubov explanation. 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.
Physical Review X
Created March 13, 2019, Updated October 29, 2019