Abstract
We present a theory for quantum impurity relaxometry of magnons in thin films, exhibiting quantitative agreement with recent experiments without needing arbitrary scale factors used in theoretical models thus far. Our theory reveals that chiral coupling between prototypical spin>1/2 quantum impurities and magnons plays a central role in determining impurity relaxation, which is further corroborated by our experiments on nickel films interfaced with nitrogen-vacancy centers. Along with advancing magnonics and understanding decoherence in hybrid quantum platforms with magnets, the ability of a quantum impurity spin to sense chiral magnetic noise presents an opportunity to probe chiral phenomena in condensed matter.
Highlights
Magnons—quanta of spin wave excitations—are fundamental to the understanding of the dynamical properties of magnetically ordered materials
Quantum impurity (QI) coupled to magnetic thin films form model systems for developing an understanding of decoherence introduced in qubits that are in close proximity to magnetic materials
Our results highlight the importance of chirality in constructing predictive models for advancing magnonics via QI relaxometry. They suggest that (i) chirality of magnon-generated fields is essential in governing decoherence of quantum systems proximal to magnetic materials and (ii) QI relaxometry can be extended to noninvasively and locally probe the physics of chiral electronic [30,31,32] and magnetic modes [33,34] living in condensed-matter systems of interest via the magnetic noise emanating from them
Summary
Magnons—quanta of spin wave excitations—are fundamental to the understanding of the dynamical properties of magnetically ordered materials. Theoretical models used to analyze experiments [13,14,17] by excluding out-of-plane magnetization fluctuations (and σm) neglect the role of chirality and require arbitrary scale factors of unknown origin to quantitatively fit the experimentally measured relaxation rates for the ms = 0 → −1 and ms = 0 → +1 transitions In this Rapid Communication, by combining the general theoretical framework of quantum relaxometry [12,15] with Landau-Lifshitz-Gilbert (LLG) phenomenology [29] for magnon dynamics in thin magnetic films, we construct a theory for QI relaxometry of magnons which inherently captures the chiral coupling. They suggest that (i) chirality of magnon-generated fields is essential in governing decoherence of quantum systems proximal to magnetic materials and (ii) QI relaxometry can be extended to noninvasively and locally probe the physics of chiral electronic [30,31,32] and magnetic modes [33,34] living in condensed-matter systems of interest via the magnetic noise emanating from them
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