Gigahertz topological phononic circuits based on micrometre-scale unsuspended waveguide arrays

The manipulation of gigahertz-frequency acoustic waves is of use in both classical and quantum applications. Topological phononics can provide robust acoustic control, but practical implementations are typically limited to low frequencies or lack scalability. Here we report reconfigurable topological phononic circuits that operate at 1.5 GHz. The approach is based on micrometre-scale unsuspended waveguides that tightly confine the acoustic waves. We use a custom-built high-resolution scanning optical vibrometer. Our visualization of the spatial evolution of topological edge states and robust Thouless pumping is in agreement with our theoretical analysis. We also develop a topological phononic Mach–Zehnder interferometer that can rapidly switch topological phonon transmission paths to provide acoustic intensity modulation with a 3 dB bandwidth of 0.65 kHz. Our work provides a reconfigurable, compact and scalable topological phononic chip that works at microwave frequencies.