Linear and nonlinear properties of a compact high-kinetic-inductance WSi multimode resonator

TL;DR

This paper investigates the linear and nonlinear characteristics of a compact WSi superconducting multimode resonator, demonstrating reduced footprint and nonlinear effects suitable for circuit QED applications.

Contribution

It provides a detailed analysis of WSi resonator properties, highlighting its potential for scalable quantum circuits with minimal degradation of quality factors.

Findings

Footprint reduced by a factor of 2.9 without quality loss

Self positive frequency shifts due to two-level systems saturation

Kerr nonlinearity characterized with a coefficient of ~1.5×10^{-7} Hz/photon

Abstract

The kinetic inductance (KI) of superconducting devices can be exploited for reducing the footprint of linear elements as well as for introducing nonlinearity to the circuit. We characterize the linear and nonlinear properties of a multimode resonator fabricated from amorphous tungsten silicide (WSi) with a fundamental frequency of \(f_1 = 172\) MHz. We show how the multimode structure of the device can be used to extract the different quality factors and to aid the nonlinear characterization. In the linear regime the footprint is reduced by a factor of \(\sim 2.9\) with standard lateral dimensions with no significant degradation of the internal quality factor compared to a similar Al device . In the nonlinear regime we observe self positive frequency shifts at low powers which can be attributed to saturation of tunneling two-level systems. The cross mode nonlinearities are described well by a Kerr model with a self-Kerr coefficient in the order of \(|K_{11}|/2\pi \approx 1.5\times10^{-7}\) Hz/photon. These properties together with a reproducible fabrication process make WSi a promising candidate for creating linear and nonlinear circuit QED elements.