Reducing soft 0-pi qubit cross-capacitance with silicon fin capacitors

A 0-pi qubit is sought after because it is a charge and phase protected qubit, but has only been experimentally realized in a soft parameter regime, where requirements have been relaxed [1,2,3]. Here, we report on progress implementing high-Q silicon fin capacitors on the soft 0-pi superconducting qubit to improve the millisecond T1 lifetimes, possibly limited by capacitor Q, and dephasing times by reducing cross-capacitances. Through higher capacitance density, the capacitors allow us to reduce capacitance of the light phi (flux) mode, while retaining the heaviness of the theta (charge) mode. This allows us to design a harder 0-pi qubit with decreased sensitivity to charge and phase noise.

[1] A. Kitaev. arXiv:cond-mat/0609441 (2006).

[2] P. Brooks, A. Kitaev, J. Preskill. Phys. Rev. A 87, 052306 (2013).

[3] A. Gyenis, P. Mundada, A. Di Paolo et. al. arXiv:1910.07542 (2019).