Millikelvin Nb nanoSQUID-embedded tuneable resonator fabricated with a neon focused-ion-beam

TL;DR

This paper presents a millikelvin Nb nanoSQUID-embedded resonator fabricated with neon focused-ion-beam, demonstrating frequency tunability and potential for coupling superconducting circuits with quantum memories.

Contribution

The work introduces a monolithic Nb nanoSQUID-embedded resonator with neon FIB fabrication, achieving operation at 16 mK and tunability, advancing hybrid superconductor-spin quantum applications.

Findings

Device operates at 16 mK with frequency tunability.

Flux sensitivity limited by dielectric noise.

Design improvements can enhance flux sensitivity.

Abstract

SQUID-embedded superconducting resonators are of great interest due to their potential for coupling highly scalable superconducting circuits with quantum memories based on solid-state spin ensembles. Such an application requires a high-$Q$, frequency-tuneable resonator which is both resilient to magnetic field, and able to operate at millikelvin temperatures. These requirements motivate the use of a higher $H_{c}$ metal such as niobium, however the challenge then becomes to sufficiently reduce the operating temperature. We address this by presenting a monolithic Nb nanoSQUID-embedded resonator, where neon focused-ion-beam fabrication of the nanoSQUID results in a device displaying frequency tuneability at $T = 16$ mK. In order to assess the applicability of the device for coupling to small spin clusters, we characterise the flux sensitivity as a function of microwave drive power and externally applied magnetic field, and find that the noise is dominated by dielectric noise in the resonator. Finally, we discuss improvements to the device design which can dramatically improve the flux sensitivity, which highlights the promise of Nb SQUID-embedded resonators for hybrid superconductor-spin applications.