Monolithic Strong Coupling of Topological Surface Acoustic Wave Resonators on Lithium Niobate

Coherent phonon transfer via high-quality factor (Q) mechanical resonator strong coupling has garnered significant interest. Yet, the practical applications of these strongly coupled resonator devices are largely constrained by their vulnerability to fabrication defects. In this study, topological strong coupling of gigahertz frequency surface acoustic wave (SAW) resonators with lithium niobate is achieved. The nanoscale grooves are etched onto the lithium niobate surface to establish robust SAW topological interface states (TISs). By constructing phononic crystal (PnC) heterostructures, a strong coupling of two SAW TISs, achieving a maximum Rabi splitting of 22 MHz and frequency quality factor product fQm of approximate to 1.2 x 1013 Hz, is realized. This coupling can be tuned by adjusting geometric parameters and a distinct spectral anticrossing is experimentally observed. Furthermore, a dense wavelength division multiplexing device based on the coupling of multiple TISs is demonstrated. These findings open new avenues for the development of practical topological acoustic devices for on-chip sensing, filtering, phonon entanglement, and beyond. The strong coupling of topological surface acoustic wave resonators with a large Rabi splitting and a high-quality factor operating at gigahertz frequencies based on a single-crystal lithium niobate acoustic-electric integrated system is realized. The coupling resonators are prepared by etching nanoscale grooves on the surface of lithium niobate. Then dense wavelength division multiplexers based on multiresonator coupling are also demonstrated. image