# Antiferromagnetic magnons as highly squeezed Fock states underlying quantum correlations

## TL;DR

This paper reveals that antiferromagnetic magnons are highly entangled, squeezed Fock states with large quantum correlations, offering new insights into their quantum nature and potential applications in magnon spintronics.

## Contribution

It introduces a quantum optical framework to describe antiferromagnetic magnons as highly entangled squeezed states, highlighting their strong quantum correlations and potential for quantum technologies.

## Key findings

- Antiferromagnetic magnons are superpositions of large numbers of sublattice-magnons.
- High entanglement exists between the two sublattices in antiferromagnetic eigenmodes.
- Antiferromagnets can serve as reservoirs for strong quantum correlations.

## Abstract

Employing the concept of two-mode squeezed states from quantum optics, we demonstrate a revealing physical picture for the antiferromagnetic ground state and excitations. Superimposed on a N{\'e}el ordered configuration, a spin-flip restricted to one of the sublattices is called a sublattice-magnon. We show that an antiferromagnetic spin-up magnon is comprised by a quantum superposition of states with $n+1$ spin-up and $n$ spin-down sublattice-magnons, and is thus an enormous excitation despite its unit net spin. Consequently, its large sublattice-spin can amplify its coupling to other excitations. Employing von Neumann entropy as a measure, we show that the antiferromagnetic eigenmodes manifest a high degree of entanglement between the two sublattices, thereby establishing antiferromagnets as reservoirs for strong quantum correlations. Based on these novel insights, we outline strategies for exploiting the strong quantum character of antiferromagetic (squeezed-)magnons and give an intuitive explanation for recent experimental and theoretical findings in antiferromagnetic magnon spintronics.