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

TL;DR

This paper introduces an efficient fabrication method for microwave absorptive filters using Eccosorb CR-124, demonstrating their effectiveness for cryogenic quantum circuit applications with high rejection, low noise, and power handling capabilities.

Contribution

The paper presents a simple, scalable fabrication process for high-performance cryogenic microwave filters with customizable cutoff frequencies and excellent thermal and power handling properties.

Findings

Achieves over 120 dB rejection up to 40 GHz.

Filters thermalize within 100 seconds at cryogenic temperatures.

Can absorb power up to 100 nW while maintaining low noise temperature.

Abstract

We present an efficient fabrication method for absorptive microwave filters based on Eccosorb CR-124. Filters are fabricated from readily available parts and their cut-off 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 as well as an error-function shaped step response without overshoot. Measurements at very low temperature show that the filters thermalize on a time scale of the order of 100 s and that they can absorb power as high as 100 nW with their noise temperature staying remarkably cool, below 100 mK. These properties make the filters ideal for cryogenic filtering and filtering of IF port signals of mixers.