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arXiv:2605.14394

Nonreciprocal magnon-magnon entanglement in a spinning cavity-magnon system

Zhisheng Xu, Mengxue Li, Chunfang Sun, Gangcheng Wang

quant-phSubmitted May 14, 2026• Announced May 15, 2026• 0 citations
arXivHTMLPDF

Abstract

Cavity-magnon systems, combining magnons and photons, offer a versatile platform for studying quantum entanglement and advancing quantum information science. In this work, we propose a scheme for generating nonreciprocal magnon-magnon entanglement in a hybrid system consisting of two yttrium iron garnet spheres coupled to a spinning whispering-gallery-mode cavity. By leveraging the magnon Kerr nonlinearity and the Sagnac effect arising from the cavity rotation, we show that the entanglement can be substantially enhanced, and the resulting entanglement exhibits pronounced nonreciprocal characteristics. Furthermore, our scheme demonstrates that the entanglement remains robust against thermal noise and persists at bath temperatures up to 100 mK. This work underscores the potential of spinning cavity-magnon systems as a versatile platform for realizing nonreciprocal quantum devices and facilitating the development of quantum technologies.

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Cavity-magnon systems, combining magnons and photons, offer a versatile platform for studying quantum entanglement and advancing quantum information science. In this work, we propose a scheme for generating nonreciprocal magnon-magnon entanglement in a hybrid system consisting of two yttrium iron garnet spheres coupled to a spinning whispering-gallery-mode cavity. By leveraging the magnon Kerr nonlinearity and the Sagnac effect arising from the cavity rotation, we show that the entanglement can be substantially enhanced, and the resulting entanglement exhibits pronounced nonreciprocal characteristics. Furthermore, our scheme demonstrates that the entanglement remains robust against thermal noise and persists at bath temperatures up to 100 mK. This work underscores the potential of spinning cavity-magnon systems as a versatile platform for realizing nonreciprocal quantum devices and facilitating the development of quantum technologies.
We propose a scheme to create nonreciprocal entanglement in a spinning cavity magnomechanical system. The setup comprises a whispering gallery mode resonator with two counterpropagating modes, simultaneously coupled to yttrium iron garnet. By spinning the resonator, the counterpropagating modes undergo an opposite Fizeau drag caused by the optical Sagnac effect. We show that in a spinning resonator, the cavity-magnon-phonon modes get entangled along a chosen direction while remaining fully uncorrelated in the other. The degree of nonreciprocity is determined by the drive detuning and the spinning velocity of the resonator. Our work provides a different route to achieve chiral control of quantum entanglement involving magnon-photon-phonon modes.
Abstract A scheme is proposed for generating and enhancing stable nonreciprocal entanglement in a spinning cavity magnomechanical system. The key components of this scheme include a ferromagnetic yttrium iron garnet sphere and a whispering gallery mode resonator supporting two counter‐propagating modes. To further optimize the performance of the system, a coherent feedback loop is introduced to reinject the dissipated energy back into the system. This not only provides an additional coupling path for the system but also effectively avoids introducing additional noise caused by measurement. The design significantly enhances both bipartite entanglement and genuine tripartite entanglement. Meanwhile, by spinning the resonator, the cavity modes experience Fizeau drag due to the optical Sagnac effect, thereby achieving nonreciprocal entanglement, which is crucial for applications such as unidirectional quantum communication channels. Additionally, the research demonstrates that even in the presence of backscattering, the entangled state can still recover significantly, highlighting the robustness of entanglement under photon backscattering. This work provides an effective method to enhance and protect quantum resources and holds important application potential for applications in quantum information processing based on magnonics.
Ultrahigh nonreciprocal transmission has been achieved in a cavity-magnon system, which consists of two whispering gallery modes (WGMs) and a single magnon mode within a magnetic insulator yttrium iron garnet sphere. The nonreciprocal frequency shift induced by the Sagnac effect enables unidirectional transmission of an input field, while suppressing propagation in the opposite direction, thereby facilitating nonreciprocal optical transmission. Within experimentally accessible parameter regimes, the optical isolation ratio can exceed 40 dB, representing the highest isolation ratio reported to date. Furthermore, applying squeezing to the magnon mode further enhances this isolation performance. Additionally, the directionality of light isolation can be reversed simply by modifying the rotation of the WGM cavity. These findings offer promising prospects for developing high-performance, tunable, and compact optical nonreciprocal devices.
Cavity magnomechanics has shown great potential in studying macroscopic quantum effects, especially for quantum entanglement, which is a key resource for quantum information science. Here we propose to realize magnon mediated nonreciprocal photon-phonon entanglement, which exhibits asymmetry when opposite magnetic or driving fields are respectively applied to the magnons with the Kerr effect or the photons with the Sagnac effect. We find that the mean magnon number can selectively exhibit nonreciprocal linear or nonlinear (bistable) behavior with the strength of the strong driving field on the cavity. Assisted by this driving field, the magnon-phonon coupling is greatly enhanced, leading to the nonreciprocal photon-phonon entanglement via the swapping interaction between the magnons and photons. This nonreciprocal entanglement can be significantly enhanced with the magnon Kerr and Sagnac effects. Given the available parameters, the nonreciprocal photon-phonon entanglement can be preserved at $\ensuremath{\approx}3$ K, showing remarkable resilience against the bath temperature. The result reveals that our paper holds promise in developing various nonreciprocal devices with both the magnon Kerr and Sagnac effects in cavity magnomechanics.
The generation of magnon entanglement and squeezing plays a crucial role in quantum information processing. In this study, we propose a scheme based on a chiral cavity-magnon system, which consists of a torus-shaped cavity and two yttrium iron garnet spheres. The magnon mode of each yttrium iron garnet sphere is selectively coupled to one of the two degenerate rotating microwave modes of the toroidal cavity. The system aims to achieve entangled and squeezed magnon states through the mediation of the cavity. We further show that bipartite entanglement can be achieved by tuning external driving parameters. Additionally, our scheme does not rely on the magnon Kerr nonlinearity, which is usually extremely weak in yttrium iron garnet spheres. This work provides insights and methods for the research of quantum states in cavity-magnon systems.
Cavity optomechanics, a promising platform to investigate macroscopic quantum effects, has been widely used to study nonreciprocal entanglement with the Sagnac effect. Here, we propose an alternative way to realize nonreciprocal entanglement among magnons, photons, and phonons in a hybrid cavity-magnon optomechanics, where the magnon Kerr effect is used. We show that the Kerr effect gives rise to a magnon frequency shift and an additional two-magnon effect. Both of them can be tuned from positive to negative via tuning the magnetic field direction, leading to nonreciprocity. By tuning system parameters such as magnon frequency detuning or the coefficient of the two-magnon effect, bipartite and tripartite entanglements can be nonreciprocally enhanced. By further studying the defined bidirectional contrast ratio, we find that nonreciprocity in our system can be switched on and off, and can be engineered by the bath temperature. Our proposal not only provides a potential path to demonstrate nonreciprocal entanglement with the magnon Kerr effect, but also opens a direction to engineer and design diverse nonreciprocal devices in hybrid cavity-magnon optomechanics with nonlinear effects.