Evanescently coupled topological ring-waveguide systems for chip-scale ultrahigh frequency phononic circuits

TL;DR

This paper demonstrates the use of topological phononic structures at microwave frequencies on a chip-scale, enabling robust, backscattering-immune elastic wave transport for advanced signal processing.

Contribution

It introduces a microscopic topological ring-waveguide system that maintains valley pseudospin polarization and demonstrates controlled phonon circulation and interference at ultrahigh frequencies.

Findings

Robust phonon transmission in topological waveguides at microwave frequencies.

Evanescent coupling enables valley-dependent interference and blocking.

Resonant phonon circulation in a tiny hexagonal ring.

Abstract

Topological phononics enabling backscattering-immune transport is expected to improve the performance of electromechanical systems for classical and quantum information technologies. Nonetheless, most of the previous demonstrations utilized macroscale and low-frequency structures and thus offered little experimental insight into ultrahigh frequency phonon transport, especially in chip-scale circuits. Here, we report microwave phonon transmissions in a microscopic topological ring-waveguide coupled system, which is an important building block for wave-based signal processing. The elastic waves in the topological waveguide evanescently couple to the ring resonator, while maintaining the valley pseudospin polarization. The resultant waves are robust to backscattering even in the tiny hexagonal ring, generating a resonant phonon circulation. Furthermore, the evanescently coupled structure allows for a critical coupling, where valley-dependent ring-waveguide interference enables blocking of the topological edge transmission. Our demonstrations reveal the capability of using topological phenomena to manipulate ultrahigh frequency elastic waves in intricate phononic circuits for classical and quantum signal-processing applications.