A soft-clamped topological waveguide for phonons

TL;DR

This paper demonstrates a topological phononic waveguide with ultra-low losses at room temperature, combining dissipation engineering and valley-Hall physics to enable robust, low-loss phonon transport suitable for advanced on-chip applications.

Contribution

It introduces a novel soft-clamped topological waveguide for phonons with unprecedented low propagation losses and quantifies backscattering protection in topological phononic systems.

Findings

Achieved 3 dB/km phonon propagation loss at room temperature.

Demonstrated 99.99% probability of phonons following sharp bends without backscattering.

Quantified backscattering protection using high-resolution ultrasound spectroscopy.

Abstract

Topological insulators were originally discovered for electron waves in condensed matter systems. Recently this concept has been transferred to bosonic systems such as photons and phonons, which propagate in materials patterned with artificial lattices that emulate spin-Hall physics. This work has been motivated, in part, by the prospect of topologically protected transport along edge channels in on-chip circuits. Importantly, even in principle, topology protects propagation against backscattering, but not against loss, which has remained limited to the dB/cm-level for phonon waveguides, be they topological or not. Here, we combine advanced dissipation engineering, in particular the recently introduced method of soft-clamping, with the concept of a valley-Hall topological insulator for phonons. This enables on-chip phononic waveguides with propagation losses of 3 dB/km at room temperature, orders of magnitude below any previous chip-scale devices. For the first time, the low losses also allow us to accurately quantify backscattering protection in a topological phonon waveguide, using high-resolution ultrasound spectroscopy. We infer that phonons follow a sharp, 120 degree-bend with a 99.99%-probability instead of being scattered back, and less than one phonon in a million is lost. The extraordinary combination of features of this novel platform suggest applications in classical and quantum signal routing, processing, and storage.