A quantum electromechanical interface for long-lived phonons

Controlling long-lived mechanical oscillators in the quantum regime holds promises for quantum information processing. Here, we present an electromechanical system capable of operating in the GHz-frequency band in a silicon-on-insulator platform. Relying on a novel driving scheme based on an electrostatic field and high-impedance microwave cavities based on TiN superinductors, we are able to demonstrate a parametrically-enhanced electromechanical coupling of g/2π = 1.1 MHz, sufficient to enter the strong-coupling regime with a cooperativity of C = 1200. The absence of piezoelectric materials in our platform leads to long mechanical lifetimes, finding intrinsic values up to τ_d = 265 μs (Q = 8.4 × 10⁶ at ωₘ/2π= 5 GHz) measured at low-phonon numbers and millikelvin temperatures. Despite the strong parametric drives, we find the cavity-mechanics system in the quantum ground state by performing sideband thermometry measurements. Simultaneously achieving ground-state operation, long mechanical lifetimes, and strong coupling sets the stage for employing silicon electromechanical resonators as memory elements and transducers in hybrid quantum systems, and as a tool for probing the origins of acoustic loss in the quantum regime.