Interface Piezoelectricity-Induced Superconducting Qubit Decoherence

Reducing the error rates of physical superconducting qubits requires further advances in the control of decoherence mechanisms. Piezoelectric interactions contribute to decoherence by mediating energy exchange between microwave photons and acoustic phonons. Centrosymmetric materials like silicon and sapphire do not display piezoelectricity and are the preferred substrates for superconducting qubits. However, the broken centrosymmetry at material interfaces may lead to piezoelectric losses in qubits. While predicted two decades ago, interface piezoelectricity has not been experimentally observed in superconducting devices. Here, I present our experimental observation of interface piezoelectricity at an aluminum-silicon junction. We performed surface acoustic wave transduction measurements and identified an effective electromechanical coupling factor of 2×10^-5%. This is comparable to weak bulk piezoelectric materials like 4H-silicon carbide. I will further demonstrate how this interface piezoelectricity contributes a significant loss channel in superconducting qubits, highlighting the need for advanced heterostructure design and phononic engineering to reduce errors in next-generation superconducting qubits.