Quasiparticle tunneling in tantalum-based transmon qubits

Quasiparticle-induced decoherence can be a significant loss mechanism in superconducting qubits. It has been shown that in aluminum transmons, such decoherence can be suppressed substantially to a negligible level, providing a clean slate for characterizing other loss mechanisms, such as dielectric loss. One promising approach to reduce dielectric loss in transmon qubits is making large features out of tantalum. However, tantalum has a superconducting gap several times higher than that of aluminum, which could lead to confinement of quasiparticles near the aluminum Josephson junction. In this work, we measure charge-parity switching rates in tantalum-based transmons to determine how quasiparticle tunneling contributes to energy relaxation in these devices.