Abstract
Dissipation-diluted and soft-clamped thin membranes exhibit extremely low mechanical loss, achieving coherent lifetimes exceeding 100 ms. This remarkable property makes them excellent platforms for exploring macroscopic quantum phenomena and new physics. In this talk, I will present my recent exploration of ultracoherent phononic devices with quantum and topological systems. First, I will discuss our progress in developing quantum transducers between microwaves and optical photons by coupling ultracoherent phononic resonators to superconducting microwave circuits and infrared optical modes. Such transducers are key components for interconnecting remote quantum systems and enabling a future quantum internet. Second, I will present our recent results on realizing ultracoherent topological phononic waveguides with propagation losses as low as 3 dB/km, a key block for phononic circuitry. This exceptionally low loss allows precise quantification of backscattering immunity, demonstrating suppression down to 1×10⁻⁴ across a 120° sharp bend. Our results are promising for the development of future ultracoherent phononic circuits, enabling new applications and providing a powerful platform for exploring fundamental physics.