Quasiparticle Transport in Asymmetric Josephson Junctions

In superconducting qubits, non-equilibrium quasiparticles may be a significant source of dissipation. Investigating the behavior of quasiparticles and the loss they produce in tunnelling may lead to improved coherence times. Asymmetric transmons, with different superconducting gaps on the left and right sides of the junction, have been fabricated to improve T₁ by reducing tunneling from non-equilibrium quasiparticles. We discuss low-temperature (T < 50 mK) current - voltage and differential conductance measurements of these asymmetric devices to characterize the behavior of the junctions. We observe distinct sub-gap current features that we attribute to multiple-Andreev reflections and estimate the junction transparency and loss of transmons made from these junctions.