Absorptive filters for quantum circuits: Efficient fabrication and cryogenic power handling

We present an efficient fabrication method for absorptive microwave filters based on Eccosorb CR-124. Filters are fabricated from readily available parts, and their cutoff frequency can be set by their length. They exhibit desirable properties such as a very large and deep stop band with rejection beyond 120 dB at least up to 40 GHz, more than 10 dB return loss in both the pass and the stop band, and an error-function shaped step response without overshoot. Measurements at very low temperatures show that the filters thermalize on a time scale of approximately 100 s, and that they can absorb power as high as 100 nW with their noise temperature staying remarkably low, below 100 mK. These properties make the filters ideal for cryogenic filtering and filtering of intermediate frequency port signals of mixers. (c) 2022 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

An efficient fabrication method for absorptive microwave filters based on Eccosorb CR-124 is presented. The filters are made from readily available parts and their cutoff frequency can be adjusted by their length. These filters exhibit desirable properties such as a wide stop band with high rejection and low return loss, as well as an error-function shaped step response without overshoot. Measurements at low temperatures show that the filters thermally stabilize quickly and can absorb high power while maintaining low noise temperature. Therefore, they are ideal for cryogenic filtering and filtering of intermediate frequency port signals of mixers.