High-impedance superconducting resonators and on-chip filters for circuit quantum electrodynamics with semiconductor quantum dots

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 ($\mathrm{Nb}\mathrm{N}$) films of different thicknesses. The kinetic inductance increases rapidly as the film thickness is reduced below 50 nm and for 15-nm $\mathrm{Nb}\mathrm{N}$ films we measure a sheet kinetic inductance $L_{k,S}=41.2\text{pH}/◻$. 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 of $f_c=8$ GHz.