Broadband electron paramagnetic resonance spectroscopy of $^{167}$Er:$^{7}$LiYF$_4$ at mK temperatures

TL;DR

This study employs broadband EPR spectroscopy at millikelvin temperatures to precisely characterize hyperfine interactions in $^{167}$Er:$^{7}$LiYF$_4$, advancing understanding of spin properties relevant for quantum memory applications.

Contribution

The paper introduces broadband EPR spectroscopy at sub-Kelvin temperatures for detailed analysis of hyperfine and quadrupole interactions in rare-earth doped crystals, providing refined spin Hamiltonian parameters.

Findings

Refined hyperfine and quadrupole interaction parameters.

Analysis of hyperfine splitting influenced by quadrupole interactions.

Demonstration of broadband EPR as a tool for characterizing hyperfine transitions.

Abstract

Rare-earth spin ensembles are a promising platform for microwave quantum memory applications due to their hyperfine transitions, which can exhibit exceptionally long coherence times when using an operation point with zero first-order Zeeman (ZEFOZ) shift. In this work, we use broadband electron paramagnetic resonance (EPR) spectroscopy on $^{167}$Er:$^{7}$LiYF$_4$ single crystals at sub-Kelvin temperatures. By fitting the spin Hamiltonian to the zero-field spectrum, we obtain refined parameters of the magnetic field-independent interactions, such as the hyperfine and quadrupole interaction. We also study the influence of the quadrupole interaction on the hyperfine splitting in the zero and low magnetic field range by analyzing EPR-spectra between 0 mT and 50 mT. Our findings highlight the broadband EPR spectroscopy approach as a powerful tool for the precise determination of the spin Hamiltonian parameters and for the characterization of hyperfine transitions in terms of their selection rules and linewidth.