PHYS838C Seminar: Kungang Li, UMD

Mon, Nov 23, 2020 4:00 pm - 5:30 pm


Speaker: Kungang Li, UMD

Title: T1 of transmons with electrodes that have different gaps.
Using double-angle evaporation we fabricated a transmon which had one electrode formed by deposition of nominally pure aluminum and the counter-electrode formed by deposition of oxygen-doped aluminum. On the same sapphire chip, during the same pump-down of the evaporator we deposited a second transmon with both electrodes made from nominally pure aluminum. The energy gaps of the electrodes depend on the film thickness and the grain size, which is affected by the oxygen doping. Measurements of the relaxation time T1 of the first device at 10 mK revealed a typical lifetime of about 200 microseconds while the second device had a typical T1 of about 90 microseconds. When T1 was measured as a function of temperature up to 300 mK, the two devices showed significantly different onset temperatures for the appearance of thermal quasiparticles.  We compared our T1 vs T results to a model based on the behavior of nonequilibrium quasiparticles residing in the electrodes and extracted the energy gap and the density of the non-equilibrium quasiparticles. Advisors: Wellstood & Lobb

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