1/f frequency fluctuations due to kinetic inductance in CoSi$_2$ microwave cavities

TL;DR

This study investigates 1/f frequency fluctuations in CoSi$_2$ superconducting microwave cavities, attributing the noise to kinetic inductance fluctuations and analyzing their dependence on temperature and power.

Contribution

It provides the first characterization of frequency noise in CoSi$_2$ microwave cavities and links the fluctuations to kinetic inductance variations.

Findings

Frequency fluctuations follow a 1/f spectral density.

Noise decreases with measurement power as 1/√P.

Fluctuations are attributed to kinetic inductance variations.

Abstract

Cobalt disilicide provides a promising nearly-epitaxial superconducting material on silicon, which is compatible with high-density integrated circuit technology. We have characterized CoSi$_{2}$ superconducting microwave cavities around 5.5 GHz for resonance frequency fluctuations at temperatures 10 - 200 mK. We found relatively weak fluctuations $(\delta f/f)^2$ following the spectral density $A/f^{\gamma} $, with $A \simeq 6 \times 10^{-16}$ and $\gamma$ slightly below 1 at an average number of photons of $10^4$; the noise decreased with measurement power as $1/P^{1/2}$. We identify the noise as arising from kinetic inductance fluctuations and discuss possible origins of such fluctuations.