Coupling erbium spins to a three-dimensional superconducting cavity at zero magnetic field

TL;DR

This paper demonstrates the coupling of erbium spins in a crystal to a superconducting cavity at zero magnetic field, revealing new spectral features and showcasing a tunable device for hybrid quantum systems.

Contribution

It presents the first experimental coupling of erbium spins to a superconducting cavity at zero magnetic field with a broad tunability and observes unexpected spectral features.

Findings

Coupling achieved at zero magnetic field with high Q factor.

Observation of asymmetric hyperfine transition lines.

Broad tunability of the superconducting cavity from 1.6 to 4.0 GHz.

Abstract

We experimentally demonstrate the coupling at zero magnetic field of an isotopically pure erbium doped yttrium orthosilicate crystal ($^{167}$Er:YSO) to a three-dimensional superconducting cavity with a $Q$ factor of $10^5$. A tunable loop-gap resonator is used, and its resonance frequency is tuned to observe the hyperfine transitions of the erbium sample. The observed spectrum differs from what is predicted by the published spin Hamiltonian parameters. The narrow cavity linewidth also enables the observation of asymmetric line shapes for these hyperfine transitions. Such a broadly tunable superconducting cavity (from 1.6 GHz to 4.0 GHz in the current design) is a promising device for building hybrid quantum systems.