Coherent driving and freezing of bosonic matter wave in an optical Lieb lattice

TL;DR

This paper demonstrates the creation and control of a flat energy band in an optical Lieb lattice using Bose-Einstein condensates, enabling exploration of flat band physics with high precision.

Contribution

It reports the first realization of a flat band in an optical Lieb lattice and investigates the dynamics and localization properties of bosons in this flat band.

Findings

Observation of localized eigenstates in the flat band

Measurement of flat band lifetime under different parameters

Detection of flat-band breaking perturbations causing delocalization

Abstract

While kinetic energy of a massive particle generally has quadratic dependence on its momentum, a flat, dispersionless energy band is realized in crystals with specific lattice structures. Such macroscopic degeneracy causes the emergence of localized eigenstates and has been a key concept in the context of itinerant ferromagnetism. Here we report the realization of a "Lieb lattice" configuration with an optical lattice, which has a flat energy band as the first excited state. Our optical lattice potential possesses various degrees of freedom about its manipulation, which enables coherent transfer of a Bose-Einstein condensate into the flat band. In addition to measuring lifetime of the flat band population for different tight-binding parameters, we investigate the inter-sublattice dynamics of the system by projecting the sublattice population onto the band population. This measurement clearly shows the formation of the localized state with the specific sublattice decoupled in the flat band, and even detects the presence of flat-band breaking perturbations, resulting in the delocalization. Our results will open up the possibilities of exploring physics of flat band with a highly controllable quantum system.