Creating synthetic spaces for higher-order topological sound transport

Modern technological advances allow for the study of systems with additional synthetic dimensions. Higher-order topological insulators in topological states of matters have been pursued in lower physical dimensions by exploiting synthetic dimensions with phase transitions. While synthetic dimensions can be rendered in the photonics and cold atomic gases, little to no work has been succeeded in acoustics because acoustic wave-guides cannot be weakly coupled in a continuous fashion. Here, we formulate the theoretical principles and manufacture acoustic crystals composed of arrays of acoustic cavities strongly coupled through modulated channels to evidence one-dimensional (1D) and two-dimensional (2D) dynamic topological pumpings. In particular, the higher-order topological edge-bulk-edge and corner-bulk-corner transport are physically illustrated in finite-sized acoustic structures. We delineate the generated 2D and four-dimensional (4D) quantum Hall effects by calculating first and second Chern numbers and physically demonstrate robustness against the geometrical imperfections. Synthetic dimensions could provide a powerful way for acoustic topological wave steering and open up a platform to explore any continuous orbit in higher-order topological matter in dimensions four and higher. The authors create synthetic dimensions in acoustic crystals composed of cavity arrays, strongly coupled through modulated channels. They provide evidence for 1D and 2D dynamic topological pumping, and show that the higher-order topological sound transport is robust against the geometrical imperfections.

Automated summary

The authors demonstrate 1D and 2D dynamic topological pumping in acoustic crystals with cavity arrays strongly coupled through modulated channels, showing the robustness of higher-order topological sound transport against geometrical imperfections.