Characterizing the attenuation of coaxial and rectangular microwave-frequency waveguides at cryogenic temperatures

TL;DR

This study measures and analyzes the attenuation of microwave waveguides at cryogenic temperatures, providing insights crucial for quantum communication and cryogenic system design.

Contribution

It offers the first detailed characterization of microwave waveguide losses at millikelvin temperatures, including frequency dependence and dielectric material properties.

Findings

Attenuation constants as low as 0.005 dB/m at millikelvin temperatures.

Frequency-dependent loss characterized using resonant-cavity technique.

Dielectric loss tangent and permittivity measured and compared with models.

Abstract

Low-loss waveguides are required for quantum communication at distances beyond the chip-scale for any low-temperature solid-state implementation of quantum information processors. We measure and analyze the attenuation constant of commercially available microwave-frequency waveguides down to millikelvin temperatures and single photon levels. More specifically, we characterize the frequency-dependent loss of a range of coaxial and rectangular microwave waveguides down to $0.005\,\rm{dB}/\rm{m}$ using a resonant-cavity technique. We study the loss tangent and relative permittivity of commonly used dielectric waveguide materials by measurements of the internal quality factors and their comparison with established loss models. The results of our characterization are relevant for accurately predicting the signal levels at the input of cryogenic devices, for reducing the loss in any detection chain, and for estimating the heat load induced by signal dissipation in cryogenic systems.