# Observation of robust flat-band localization in driven photonic rhombic lattices

## TL;DR

This paper demonstrates that flat-band states in driven photonic rhombic lattices remain localized despite external modulations, due to destructive interference and lattice symmetry, with observed phenomena including Bloch oscillations.

## Contribution

It shows the robustness of flat-band localization in photonic lattices under external driving, a novel insight into wave interference and lattice symmetry effects.

## Key findings

- Flat-band states do not diffract under static and high-frequency drivings.
- Destructive interference maintains localization despite external modulation.
- Observed Bloch oscillations and coherent destruction of tunneling.

## Abstract

We demonstrate that a flat-band state in a quasi-one-dimensional rhombic lattice is robust in the presence of external drivings along the lattice axis. The lattice was formed by periodic arrays of evanescently coupled optical waveguides, and the external drivings were realized by modulating the paths of the waveguides. We excited a superposition of flat-band eigenmodes at the input and observed that this state does not diffract in the presence of static as well as high-frequency sinusoidal drivings. This robust localization is due to destructive interference of the analogous wavefunction and is associated with the symmetry in the lattice geometry. We then excited the dispersive bands and observed Bloch oscillations and coherent destruction of tunneling. {\textcopyright} 2017 Optical Society of America.