Second-order correlation and squeezing of photons in cavities with ultrastrong magnon-photon interactions

TL;DR

This paper explores how ultrastrong magnon-photon interactions in cavity systems induce quadrature squeezing and quantum correlations, revealing distinct behaviors in ferromagnetic and antiferromagnetic setups, with implications for quantum information processing.

Contribution

It provides exact solutions for second-order correlation functions in ultrastrong coupling regimes, demonstrating how anisotropic couplings enhance squeezing without increasing photon numbers.

Findings

Counter-rotating interactions induce quadrature squeezing.

Tuning anisotropic couplings enhances squeezing.

Ferromagnetic and antiferromagnetic cavities show different quantum correlation behaviors.

Abstract

We investigate the second-order photon correlation function in cavity-magnon systems, focusing on ferromagnetic and antiferromagnetic cavities within the ultrastrong coupling regime, and extending beyond the rotating-wave approximation. By deriving exact integral solutions for the second-order correlation function, we demonstrate that counter-rotating magnon-photon interactions induce quadrature squeezing in the cavity mode. Furthermore, we show that tuning the anisotropic magnon-cavity couplings enhances the squeezing effect by changing the level repulsion of the magnon-cavity photon hybrid mode without increasing the cavity photon occupation number. Our study reveals distinct quantum correlation behaviors in ferromagnetic and antiferromagnetic cavities: For ferromagnetic cavities, we show that squeezing increases with coupling strength asymmetry, whereas in the antiferromagnetic case, magnon modes with opposite chirality suppress quantum effects and impose a lower bound on correlation functions. These findings provide a pathway to optimize photon blockade for quantum information technology in magnon-cavity systems in the ultrastrong coupling limit.