Long-lived transmons with different electrode layouts

To test the contribution of non-equilibrium quasiparticles to qubit relaxation, we have repeatedly measured relaxation time T1 in Al/AlOx/Al transmons with electrodes that different superconducting gaps. In one device, first layer electrode was formed by thermal evaporation nominally pure Al, while counter-electrode deposition oxygen-doped which gave a larger gap value. The long, but showed large fluctuations, varying between about 100 and 300 μs at 20 mK. other transmons, Al. These devices similar range fluctuating values, maximum values over 200 μs. did not depend strongly on temperature below 150 mK, dropped rapidly above this due thermally generated quasiparticles.