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arXiv:2504.08562 · Physical review. B./Physical review. B

Magnon and photon blockade in a hybrid antiferromagnet-cavity quantum system

Vemund Falch, Arne Brataas, Alireza Qaiumzadeh

Published Aug 25, 2025• 9 citations
arXivHTMLPDF

Abstract

We investigate both magnon and photon blockade for an antiferromagnetic insulator coupled to a linearly polarized cavity mode. We focus on the cross-Kerr nonlinearity between the two magnon modes, which can be large in antiferromagnets with a weak easy-axis magnetic anisotropy. By numerically solving the Lindblad master equations, we demonstrate that the resulting bright and dark modes, i.e., system eigenmodes that couple strongly and weakly to photons, respectively, exhibit distinct behaviors. The bright mode exhibits both magnon and photon blockade due to a weak effective nonlinearity, while the dark mode only exhibits magnon blockade for a detuned cavity photon. The blockade efficiency can further be optimized by appropriately tuning the competing interactions in the system. In addition, we show that applying a DC magnetic field, which lifts the degeneracy of antiferromagnetic chiral magnon eigenmodes, destroys the dark mode and leads to an unconventional photon blockade. These findings provide a pathway for generating single magnon and photon states useful for quantum information technology based on the underlying large squeezing of antiferromagnetic magnons.

DOI
10.1103/m2rq-l6fl

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We investigate both magnon and photon blockade for an antiferromagnetic insulator coupled to a linearly polarized cavity mode. We focus on the cross-Kerr nonlinearity between the two magnon modes, which can be large in antiferromagnets with a weak easy-axis magnetic anisotropy. By numerically solving the Lindblad master equations, we demonstrate that the resulting bright and dark modes, i.e., system eigenmodes that couple strongly and weakly to photons, respectively, exhibit distinct behaviors. The bright mode exhibits both magnon and photon blockade due to a weak effective nonlinearity, while the dark mode only exhibits magnon blockade for a detuned cavity photon. The blockade efficiency can further be optimized by appropriately tuning the competing interactions in the system. In addition, we show that applying a DC magnetic field, which lifts the degeneracy of antiferromagnetic chiral magnon eigenmodes, destroys the dark mode and leads to an unconventional photon blockade. These findings provide a pathway for generating single magnon and photon states useful for quantum information technology based on the underlying large squeezing of antiferromagnetic magnons.
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.
Currently there is a growing interest in studying the coherent interaction between magnetic systems and electromagnetic radiation in a cavity, prompted partly by possible applications in hybrid quantum systems. We propose a multimode cavity optomagnonic system based on antiferromagnetic insulators, where optical photons couple coherently to the two homogeneous magnon modes of the antiferromagnet. These have frequencies typically in the THz range, a regime so far mostly unexplored in the realm of coherent interactions, and which makes antiferromagnets attractive for quantum transduction from THz to optical frequencies. We derive the theoretical model for the coupled system, and show that it presents unique characteristics. In particular, if the antiferromagnet presents hard-axis magnetic anisotropy, the optomagnonic coupling can be tuned by a magnetic field applied along the easy axis. This allows us to bring a selected magnon mode into and out of a dark mode, providing an alternative for a quantum memory protocol. The dynamical features of the driven system present unusual behavior due to optically induced magnon-magnon interactions, including regions of magnon heating for a red-detuned driving laser. The multimode character of the system is evident in a substructure of the optomagnonically induced transparency window.
Hybrid quantum states consisting of single photons and single magnons are valuable quantum resources for realizing multiple quantum information tasks. The blockade effects of magnons and photons in a cavity–magnon–qubit system are investigated, where an auxiliary microwave cavity is simultaneously coupled with an yttrium iron garnet sphere, a qubit, and another microwave cavity. The modes of the auxiliary cavity are adiabatically eliminated, and the virtual photons in the auxiliary cavity mediate the coupling between the magnon mode and photon mode. When the system parameters satisfy both conventional and unconventional blockade conditions, both the magnon/photon auto‐correlation and magnon–photon cross‐correlation are weak, indicating that magnons and photons tend to exist alone in the system. When the system parameters only satisfy unconventional blockade conditions, strong magnon–photon cross‐correlation can be exhibited, indicating that magnons and photons tend to exist simultaneously in the system. The proposal presents a method for preparing magnon–photon pairs, which may have potential applications in quantum information sciences and technologies.
ABSTRACT Photon blockade is a key quantum effect for generating single‐photon sources essential to quantum information processing. Compared with unconventional photon blockade, the conventional counterpart provides higher single‐photon generation efficiency but typically demands strong nonlinearity, which severely restricts experimental feasibility. Here, a nonlinear enhancement scheme based on a hybrid optomagnonic system is proposed. The central idea is to exploit an additional tripartite interaction among the TE mode, TM mode, and magnon that, under strong driving, induces two‐mode squeezing. Via a squeezing transformation, the effective magnon–photon coupling is exponentially enhanced, giving rise to a strong effective Kerr nonlinearity and thus an increased energy‐level detuning. Using both analytical calculations and numerical simulations of the second‐order correlation function, it is shown that the conventional photon blockade is substantially enhanced. Compared with the pure optomagnonic scheme induced by the Faraday effect, the proposed approach reduces the second‐order correlation function by more than an order of magnitude and dramatically broadens the blockade parameter window. Moreover, photon blockade is achieved even when the intrinsic coupling strength is much smaller than the cavity decay rate. These results suggest a feasible route toward high‐efficiency conventional photon blockade without strong intrinsic nonlinearities, potentially facilitating on‐chip single‐photon sources for scalable quantum information processing.
Magnon blockade is an effective physical mechanism to generate a single magnon, which is of great importance in quantum information processing. We present a scheme to realize the unconventional magnon blockade effect by using Kerr nonlinearity in a cavity electromagnonic system. Under weak driving conditions, we give the optimal parameter conditions for magnon antibunching through analytical calculations, which are in good agreement with numerical results. Furthermore, we find that Kerr nonlinearity is necessary to create magnon blockade. In particular, unconventional magnon blockade can be achieved in both weak nonlinearity and weak coupling regimes. The present scheme indicates a method for generating unconventional magnon blockade effect and provides a feasible and flexible platform for the realization of a single-magnon source with high purity.
We propose an scheme for directional single-photon source based on a chiral cavity-magnon system. In this system, the magnon mode in a single-crystal yttrium iron garnet (YIG) sphere is coupled to only one of two rotating microwave modes in the torus-shaped microwave cavity. When two-photon drives are applied to both ports of the waveguide, the chiral cavity-magnon coupling leads to an unconventional photon blockade in one propagation direction, resulting in directional single-photon emission. The emission direction of the single-photon source can be controlled by reversing the biased magnetic field. Furthermore, we further examine the effects of imperfect chiral cavity-magnon coupling and the coupling between the two cavity modes on the photon blockade behavior. The results show that the system retains robustness in the presence of these nonideal factors, and the unidirectional photon blockade effect remains clearly preserved.