Floquet engineering of individual band gaps in an optical lattice using a two-tone drive

TL;DR

This paper demonstrates how two-tone Floquet driving can selectively open and close individual band gaps in an optical lattice, enabling precise control over band topology in ultracold atomic systems.

Contribution

It introduces a comprehensive theoretical and experimental framework for Floquet engineering of band gaps using two-frequency modulation in optical lattices.

Findings

Successful experimental control of band gap closing and reopening.

Quantitative agreement between theory and experiment.

Analytic model including multi-photon and interference effects.

Abstract

The dynamic engineering of band structures for ultracold atoms in optical lattices represents an innovative approach to understand and explore the fundamental principles of topological matter. In particular, the folded Floquet spectrum determines the associated band topology via band inversion. We experimentally and theoretically study two-frequency phase modulation to asymmetrically hybridize the lowest two bands of a one-dimensional lattice. Using quasi-degenerate perturbation theory in the extended Floquet space we derive an effective two-band model that quantitatively describes our setting. The energy gaps are experimentally probed via Landau-Zener transitions between Floquet-Bloch bands using an accelerated Bose-Einstein condensate. Separate and simultaneous control over the closing and reopening of these band gaps is demonstrated. We find good agreement between experiment and theory, establishing an analytic description for resonant Floquet-Bloch engineering that includes single- and multi-photon couplings, as well as interference effects between several commensurate drives.