Observation of pi/2 modes in an acoustic Floquet system

TL;DR

This paper experimentally demonstrates the existence of pi/2 topological modes in an acoustic Floquet system, revealing new boundary states that could lead to advanced quantum phenomena and applications.

Contribution

The study provides the first experimental verification of pi/2 modes in an acoustic system simulating a driven topological model, bridging theory and practical observation.

Findings

Confirmed 4T-periodicity as signature of pi/2 modes

Designed acoustic waveguide array simulating a driven topological model

Theoretically validated the experimental observations

Abstract

Topological phases of matter have remained an active area of research in the last few decades. Periodic driving is known to be a powerful tool for enriching such exotic phases, which leads to various phenomena with no static analogs. One such phenomenon is the emergence of the elusive $pi/2$ modes, i.e., a type of topological boundary state pinned at a quarter of the driving frequency. The latter may lead to the formation of Floquet parafermions in the presence of interaction, which is known to support more computational power than Majorana particles. In this work, we experimentally verify the signature of $\pi/2$ modes in an acoustic waveguide array, which is designed to simulate a square-root periodically driven Su-Schrieffer-Heeger model. This is accomplished by confirming the $4T$-periodicity ($T$ being the driving period) profile of an initial-boundary excitation, which we also show theoretically to be the smoking gun evidence of $\pi/2$ modes. Our findings are expected to motivate further studies of $\pi/2$ modes in quantum systems for potential technological applications.