Dynamics of Non-equilibrium Quasiparticles in Transmon Qubits

We have studied the diffusion, trapping, and recombination dynamics of non-equilibrium quasiparticles for different transmon qubits. To generate an excess density of low energy quasiparticles in the transmon device, the read-out resonator was pumped with a large amplitude rf signal, which induced quasiparticle-quasiparticle tunneling through the transmon's Al/AlOx/Al junction and thus generating an excess density near the junction. By modeling the recovery in time of T1 and T2 after initially injecting the quasiparticles and simulating the data using a simple numerical model, we can determine the rates for quasiparticle diffusion, trapping, and recombination. We will discuss observed differences in recovery characteristics and induced rates between transmons with and without a direct galvanic connection to ground, and between shunting capacitors made of Al and Ta.