Hot electron measurements below 100 mK for quantum devices*

Recently, the electron-phonon coupling constant of the resistive alloy material nichrome (NiCr) was estimated as ΣNiCr = (5 x 10⁸) Wm^-3K^-5 from measurements of the dephasing rate of a superconducting transmon qubit coupled to a NiCr attenuator [1]. In this talk, we will discuss ongoing measurements to more directly measure the electron temperature and find the electron-phonon coupling constant of NiCr. In particular, we have fabricated NIS junctions consisting of NiCr/AlOx/Al structures and measured the current voltage characteristics at temperatures down to 20 mK. These measurements will be used to extract the electron temperature of the NiCr material which can be compared to the previously reported value, allowing for more accurate thermal modeling of future NiCr devices.

[1] Jen-Hao Yeh, Jay LeFebvre, Shavindra Premaratne, F. C. Wellstood, and B. S. Palmer, Journal of Applied Physics 121, 224501 (2017); https://doi.org/10.1063/1.4984894