Quantum-impurity relaxometry of magnetization dynamics

TL;DR

This paper develops a framework for using quantum-impurity relaxometry, such as with NV centers, to noninvasively probe collective spin excitations and dynamics in magnetic insulators, including magnons and spin-wave transport.

Contribution

It introduces a general theoretical framework linking quantum-impurity relaxation rates to magnetic system properties, enabling detection of coherent spin phenomena.

Findings

Quantum-impurity relaxometry can detect magnon condensation.

Framework relates relaxation rates to magnetic noise properties.

Potential to probe spin-wave transport regimes noninvasively.

Abstract

Prototypes of quantum impurities (QI), such as NV and SiV centers in diamond, have been recently growing in popularity due to their minimally invasive and high-resolution magnetic field sensing. Here, we focus on quantum-impurity relaxometry as a method to probe collective excitations in magnetic insulators. We develop a general framework that relates the experimentally-measurable quantum-impurity relaxation rates to the properties of a magnetic system via the noise emitted by the latter. We suggest that, when the quantum-impurity frequency lies within the spin-wave gap, quantum-impurity relaxometry can be effectively deployed to detect signatures of the coherent spin dynamics, such as magnon condensation, both in ferromagnetic and antiferromagnetic systems, as well as open prospects to nonintrusively probe spin-wave transport regimes in magnetic insulators.