Antiferromagnetic Resonance Revisited: Dissipative Coupling without Dissipation

TL;DR

This paper reveals that antiferromagnetic excitations can be understood as a non-Hermitian system with dissipative coupling, leading to level attraction in resonance spectra even without dissipation, and enabling quantum entanglement applications.

Contribution

It introduces a novel perspective on antiferromagnetic resonance as a non-Hermitian phenomenon arising from $ ext{PT}$-symmetry, explaining observed behaviors without dissipation.

Findings

Antiferromagnetic excitations exhibit level attraction instead of repulsion.

Antiferromagnetic ground state is $ ext{PT}$-symmetric, leading to non-Hermitian behavior.

Magnons can generate quantum entanglement without external pumping.

Abstract

The antiferromagnet is a closed Hermitian system, we find that its excitations, even in the absence of dissipation, can be viewed as a non-Hermitian system with dissipative coupling. Consequently, the antiferromagnetic resonance spectrum does not show the typical level repulsion, but shows the level attraction -- a characteristic behavior often observed in non-Hermitian systems. Such behavior is because the antiferromagnetic ground state is $\mathcal{PT}$-symmetric. This new understanding on antiferromagnetic resonance also explains the mysterious enhancement of antiferromagnetic damping rate. Being effectively non-Hermitian, antiferromagnetic magnons can be used for quantum entanglement generation without introducing a third party like external pumping.