Coupling of a locally implanted rare-earth ion ensemble to a superconducting micro-resonator

TL;DR

This paper demonstrates the successful coupling of locally implanted Gd$^{3+}$ ions in Al$_{2}$O$_{3}$ to a superconducting NbN micro-resonator, maintaining high quality factors and enabling detailed spectroscopy of the spin-resonator interaction.

Contribution

It introduces a controlled ion implantation method to couple rare-earth ions to superconducting resonators without degrading their quality, advancing hybrid quantum device fabrication.

Findings

Achieved coupling rates of about 1 MHz.

Maintained resonator quality factors above 10^5.

Observed electron-spin resonances consistent with models.

Abstract

We demonstrate the coupling of rare-earth ions locally implanted in a substrate (Gd$^{3+}$ in Al$_{2}$O$_{3}$) to a superconducting NbN lumped-element micro-resonator. The hybrid device is fabricated by a controlled ion implantation of rare-earth ions in well-defined micron-sized areas, aligned to lithographically defined micro-resonators. The technique does not degrade the internal quality factor of the resonators which remain above $10^{5}$. Using microwave absorption spectroscopy we observe electron-spin resonances in good agreement with numerical modelling and extract corresponding coupling rates of the order of $1$ MHz and spin linewidths of $50 - 65$ MHz.