Characterising superconducting filters using residual microwave background

TL;DR

This study uses a hybrid single-electron trap to analyze the microwave background and characterize superconducting filters, revealing millimeter wave propagation in superconducting systems relevant for quantum devices.

Contribution

It introduces a novel method employing a single-electron trap for spectrum analysis at extremely low signal levels in superconducting systems.

Findings

Probing millimeter wave propagation in superconducting systems.

Modeling of superconducting components with simple theoretical descriptions.

Insights into the behavior of superconducting filters at high frequencies.

Abstract

A normal metal - superconductor hybrid single-electron trap with tunable barrier is utilized as a tool for spectrum analysis at the extremely low signal levels, using only well filtered cryogenic microwave background as a photon source in the frequency range from about 50 to 210 GHz. We probe millimeter wave propagation in two superconducting systems: a Josephson junction array around its plasma frequency, and a superconducting titanium film in the limit when the photon energies are larger than the superconducting energy gap. This regime is relevant for improving the performance of cryogenic quantum devices but is hard to access with conventional techniques. We show that relatively simple models can be used to describe the essential properties of the studied components.