Probing defect-mediated electromechanical coupling in silicon

Material defects known as two-level systems (TLS) are a dominant source of energy loss in superconducting qubits. The microscopic picture assumes that TLSs couple electrically to the qubit and relax by emitting phonons through their elastic dipole transition, thereby mediating qubit decay. However, this TLS-mediated decay pathway has not been directly verified. Prior single TLS experiments have probed TLS-qubit electric coupling with static strain tuning of TLS energies, but TLS dynamic coupling to both microwave and mechanical fields remains largely unexplored.

In this work, we investigate defect-mediated electromechanical coupling at the single-TLS level by embedding a silicon nanomechanical resonator inside the capacitor of a high-impedance microwave resonator. This device architecture allows probing coherent interactions between TLS, microwave, and mechanical degrees of freedom. I will discuss the experimental platform, signatures of strongly coupled TLSs, and implications for testing the microscopic model of TLS-induced energy decay.