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arXiv · 2301.04555

Long-lived transmons with different electrode layouts

Kungang Li·S. K. Dutta·Zachary Steffen·Dylan Poppert·Shahriar Keshvari·Jeffery Bowser·B. S. Palmer·C. J. Lobb·F. C. Wellstood
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Abstract

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.

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Kungang Li, S. K. Dutta, Zachary Steffen, Dylan Poppert, Shahriar Keshvari, Jeffery Bowser, B. S. Palmer, C. J. Lobb, F. C. Wellstood. 2023-01-11. Long-lived transmons with different electrode layouts. https://arxiv.org/abs/2301.04555

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