Observation of Interface-Piezoelectric Loss in Transmon Qubits on Silicon

We report the observation of interface piezoelectricity-induced dissipation in transmon qubits fabricated on high-resistivity silicon substrates. Piezoelectric coupling at the aluminum–silicon interface has been identified as a possible source of electromechanical loss in superconducting devices. In our experiment, we fabricated transmon qubits whose shunt capacitor also serves as a surface acoustic wave (SAW) transducer. The device is placed  inside a SAW cavity to enhance the electromechanical interaction. When the qubit frequency is tuned into resonance with a cavity mode, the qubit lifetime T₁ is reduced by approximately a factor of two, indicating significant electromechanical energy exchange. This observation provides direct evidence of interface piezoelectric losses as a new superconducting qubit dissipation mechanism. Our experiments show that in certain qubit geometries, interface piezoelectric losses can dominate over dielectric loss from two-level systems. It also reveals a potentially engineerable pathway for coupling superconducting circuits with phononic systems.