Developing high-impedance superconducting resonators and on-chip filters for semiconductor quantum dot circuit quantum electrodynamics

TL;DR

This paper investigates niobium nitride films for high-impedance superconducting resonators and filters, demonstrating enhanced kinetic inductance and effective microwave attenuation for quantum dot circuit QED applications.

Contribution

It introduces the fabrication and characterization of high kinetic inductance NbN films and their application in compact on-chip filters for improved cQED device performance.

Findings

Kinetic inductance increases as NbN film thickness decreases below 50 nm.

15 nm NbN films exhibit sheet kinetic inductance of 41.2 pH/□.

Fabricated filters achieve up to 60 dB attenuation at 8 GHz.

Abstract

Spin-photon coupling presents an enticing opportunity for the long-range coupling of spin qubits. The spin-photon coupling rate $g_{s}$ is proportional to the charge-photon coupling rate $g_{c}$. To move deeper into the strong coupling regime, $g_{c}$ can be enhanced by fabricating high-impedance cavities using high kinetic inductance films. Here we report dc transport and microwave response investigations of niobium nitride (NbN) films of different thicknesses. The kinetic inductance increases rapidly as the film thickness is reduced below 50 nm and for 15 nm NbN films we measure a sheet kinetic inductance $L_{k,S}$ = 41.2 pH/$\Box$. As an application of the high kinetic inductance films, we fabricate compact LC filters that are commonly used to reduce microwave leakage in circuit quantum electrodynamics (cQED) devices. These filters feature up to 60 dB of attenuation near typical cavity resonance frequencies $f_c$ = 8 GHz.