  To test the contribution of non-equilibrium quasiparticles to qubit
relaxation, we have repeatedly measured the relaxation time T_1 in Al/AlOx/Al
transmons with electrodes that have different superconducting gaps. In one
device, the first layer electrode was formed by thermal evaporation of
nominally pure Al, while the counter-electrode was formed by deposition of
oxygen-doped Al, which gave a larger gap value. The relaxation time was long,
but showed large fluctuations, with T_1 varying between about 100 and 300
{\mu}s at 20 mK. In other transmons, we formed the first layer electrode by
deposition of oxygen-doped Al, while the counter-electrode was formed by
deposition of nominally pure Al. These devices showed a similar range of large
and fluctuating T_1 values, with maximum T_1 values over 200 {\mu}s. The
relaxation time of the devices did not depend strongly on temperature below
about 150 mK, but dropped rapidly above this due to thermally-generated
quasiparticles.
