Interband heating processes in a periodically driven optical lattice

TL;DR

This paper studies how periodic driving in optical lattices causes interband heating, identifying thresholds and suppression effects, which are crucial for Floquet engineering of topological and magnetic properties.

Contribution

It provides numerical and analytical analysis of interband excitation processes in driven optical lattices, highlighting threshold behaviors and their implications for Floquet engineering.

Findings

Interband excitations are exponentially suppressed below a threshold driving strength.

A sudden onset of interband heating occurs at low frequencies once the threshold is reached.

The results are applicable to various periodically driven lattice systems for Floquet engineering.

Abstract

We investigate multi-"photon" interband excitation processes in an optical lattice that is driven periodically in time by a modulation of the lattice depth. Assuming the system to be prepared in the lowest band, we compute the excitation spectrum numerically. Moreover, we estimate the effective coupling parameters for resonant interband excitation processes analytically, employing degenerate perturbation theory in Floquet space. We find that below a threshold driving strength, interband excitations are suppressed exponentially with respect to the inverse driving frequency. For sufficiently low frequencies, this leads to a rather sudden onset of interband heating, once the driving strength reaches the threshold. We argue that this behavior is rather generic and should also be found in lattice systems that are driven by other forms of periodic forcing. Our results are relevant for Floquet engineering, where a lattice system is driven periodically in time in order to endow it with novel properties like the emergence of a strong artificial magnetic field or a topological band structure. In this context, interband excitation processes correspond to detrimental heating.