Millikelvin thermal and electrical performance of lossy transmission line filters

TL;DR

This study investigates the low-temperature electrical and thermal performance of lossy transmission line filters, demonstrating stable transmission characteristics and minimal Johnson noise emission at millikelvin temperatures, relevant for quantum computing applications.

Contribution

It provides detailed measurements of scattering parameters and Johnson noise of low-pass stripline filters at millikelvin temperatures, highlighting their suitability as matched thermal loads in cryogenic environments.

Findings

Transmission remains stable down to 25 mK.

Johnson noise emission is consistent with a few millikelvin temperature difference.

Filters can serve as effective thermal loads at millikelvin temperatures.

Abstract

We report on the scattering parameters and Johnson noise emission of low-pass stripline filters employing a magnetically loaded silicone dielectric down to 25 mK. The transmission characteristic of a device with $f_{-3dB}$=1.3 GHz remains essentially unchanged upon cooling. Another device with $f_{-3dB}$=0.4 GHz, measured in its stopband, exhibits a steady state noise power emission consistent with a temperature difference of a few mK relative to a well-anchored cryogenic microwave attenuator at temperatures down to 25 mK, thus presenting a matched thermal load.