Decreased Transmon T1 and Increased Pe from High Resonator Drive Power

We discuss detrimental effects on the lifetime T1 and initial excited state population (Pe) of a 6 GHz Al/AlOx/Al transmon when pumping the read-out resonator at large powers. In our device, the qubit is coupled to an 8 GHz Al resonator that is in turn coupled to an input-output transmission line for measuring the resonator. Using a low power dispersive readout, we find T1 ~ 30us and Pe ~ 0.36%. On the other hand, when pumping the resonator at high powers, slightly above the Jaynes-Cummings nonlinear readout point[1], T1 decreases to 2 us and the excited state population increases more than an order of magnitude to Pe ~ 10%. After a high power pulse, T1 recovers on a time scale that is consistent with quasiparticle tunneling through the junction being the dominant loss mechanism[2]. On the other hand, as we will discuss, Pe has a non-trivial dependence on the detuning of the drive from the qubit transition frequency. 

[1]Reed et al., Phys. Rev. Lett. 105, 173601 (2010).

[2]Wang et al., Nat. Commun. 5, 5836 (2014)