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Advanced Quantum Technologies

Enhancement of Microwave Entanglement via Coherent Quantum Feedback with Cavity Magnonics

Yue‐Han Lin, Rong‐Can Yang, Zhi‐Bo Yang, Hong‐Yu Liu

Published Jul 18, 2025• 2 citations
Publisher

Abstract

Abstract Entangled microwave fields are a crucial resource for quantum information processing and quantum computation. Here a scheme is presented to enhance quantum entanglement between two microwave cavity modes using coherent quantum feedback in cavity magnonics. The system consists of a planar cross‐line cavity that includes two microwave cavity modes, with a ferrimagnetic yttrium‐iron‐garnet (YIG) sphere positioned at the intersection of these modes. The magnon mode confined in the YIG sphere can simultaneously be coupled to both microwave cavity modes via magnetic dipole interaction. Additionally, a coherent feedback loop is integrated into one of the cavity modes to modulate its frequency detuning and dissipation. These results demonstrate that feedback control can effectively reduce the dissipation and effective environmental temperature, thereby relaxing the stringent requirement of quantum state generation on extremely low bath temperatures. Furthermore, by enhancing the feedback signal to reduce the high power requirement for activating magnon Kerr effect, the feasibility of the experiment is significantly improved. The scheme finds broad applications in many quantum tasks that require microwave entanglement and other research field that needs to cool quantum systems.

DOI
10.1002/qute.202500296

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Abstract Entangled microwave fields are a crucial resource for quantum information processing and quantum computation. Here a scheme is presented to enhance quantum entanglement between two microwave cavity modes using coherent quantum feedback in cavity magnonics. The system consists of a planar cross‐line cavity that includes two microwave cavity modes, with a ferrimagnetic yttrium‐iron‐garnet (YIG) sphere positioned at the intersection of these modes. The magnon mode confined in the YIG sphere can simultaneously be coupled to both microwave cavity modes via magnetic dipole interaction. Additionally, a coherent feedback loop is integrated into one of the cavity modes to modulate its frequency detuning and dissipation. These results demonstrate that feedback control can effectively reduce the dissipation and effective environmental temperature, thereby relaxing the stringent requirement of quantum state generation on extremely low bath temperatures. Furthermore, by enhancing the feedback signal to reduce the high power requirement for activating magnon Kerr effect, the feasibility of the experiment is significantly improved. The scheme finds broad applications in many quantum tasks that require microwave entanglement and other research field that needs to cool quantum systems.
Abstract The scheme is proposed to enhance the entanglement in cavity‐magnonics system by exploiting the synergistic effects of an optical parametric amplifier (OPA) and coherent feedback. In the system, the two cavities are arranged in a cross‐shaped, with a yttrium iron garnet (YIG) sphere positioned near the intersection of the cross‐shaped cavities. By introducing coherent feedback, the energy dissipated by the horizontal cavity can be fed back into the vertical cavity, which can be compensated via OPA. The nonlinear gain of OPA and reflectivity of the coherent feedback play important roles in the dynamics of the system and enable enhancement of both bipartite and tripartite entanglement as compared to the system without OPA and coherent feedback. The robustness of entanglement against environment temperature can also be greatly improved. Moreover, in the system that possesses a symmetrical structure but demonstrates asymmetric energy flow, controllable one‐way steering can be realized through the precise adjustment of specific parameters within the system. The scheme offers a novel approach to realize high‐quality entanglement resources and holds potential applications in quantum information processing and quantum communication.
Abstract A scheme is proposed to enhance quantum correlation, including entanglement and steering, for two magnon modes in a cavity‐magnon hybrid system through coherent quantum feedback. The hybrid system consists of a microwave cavity and two YIG spheres, which incorporates a nonlinear flux‐driven Josephson parametric amplifier in order for the generation of two photons within the cavity simultaneously. A quantum coherent feedback loop is used for the reduction of effective dissipation. By modulating feedback parameters, optimal bipartite and tripartite entanglement, as well as quantum steering are derived. Importantly, compared with the same setup without coherent feedback, the proposed scheme significantly improves quantum correlation. Furthermore, by optimizing the feedback reflectivity and the ratio of cavity‐magnon coupling strength, the enhancement of asymmetric steering can be controlled. Notably, incorporating the feedback loop effectively increase its robustness against thermal noise, thus the scheme offer better prospect for experimental development. This study paves the way for advancements in quantum information processing and quantum entanglement within cavity‐magnonics.
Abstract A scheme is proposed to prepare quantum entanglement and quantum steering between two indirectly coupled microwave cavity modes within a hybrid cavity magnonic system. The system consists of two microwave cavities individually coupled to a common YIG sphere driven by a two‐tone Floquet field, while the output field of the second microwave cavity is fed back into the input port of the first microwave cavity via a coherent feedback loop. Floquet driving can effectively generate two interactions between magnons and photons. Magnons with higher dissipation can serve as a cooling channel for the two cavity modes. Optimal quantum correlations between the cavity modes can be achieved when the competition between these two interactions reaches equilibrium. Subsequently, a comparative analysis is performed on the evolution of quantum correlation with and without coherent feedback, revealing that the presence of a coherent feedback loop in the system not only significantly enhances entanglement and steering but also induces inherent asymmetry in quantum steering regardless of the decay rates within subsystems. Moreover, under the influence of the coherent feedback loop, the enhanced quantum correlations exhibit increased robustness against rising environmental temperatures. This work significantly expands the validity of implementation and provides a promising avenue for the preparation of stable quantum correlations.
Abstract This paper proposes a novel scheme to enhance the photon blockade effect in a cavity‐magnon system via coherent feedback loops. The system comprises a microwave cavity, a coherent feedback loop, and a yttrium iron garnet sphere. The cavity mode is coupled to the magnon mode via magnetic dipole interaction and is driven by both a two‐photon driving field and a weak pump field. The statistical properties of photons are characterized through the second‐order correlation function. Research findings indicate that coherent feedback significantly enhances the photon blockade effect, with the underlying physical mechanism being the effective reduction of the average two‐photon number. After introducing the two‐photon driving field, the optimal driving intensity and phase conditions for achieving photon blockade through analytical calculations are obtained. Under these optimal parameters, the proposed scheme demonstrates a low reflection coefficient, thereby ensuring excellent experimental feasibility and flexible controllability. This study offers new insights into the design of tunable single‐photon sources and establishes a novel research platform based on coherent feedback control for realizing photon blockade.
Abstract A scheme is proposed for generating entanglement and achieving perfect one‐way EPR (Einstein–Podolsky–Rosen) steering in a cross‐shaped cavity magnonics system via the Kerr effect arising from magnetocrystalline anisotropy. The scheme involves two microwave cavities with distinct quality factors that simultaneously couple to a magnon mode of a macroscopic yttrium‐iron‐garnet sphere via the magnetic‐dipole interaction. It is demonstrated that both the bipartite and tripartite entanglement among the three modes will be generated due to Kerr nonlinearity, and the perfect one‐way EPR steering will also be achieved between the cavity with higher quality factor and the magnon mode. Notably, this scheme differs from conventional protocols that produce asymmetric EPR steering by introducing additional unbalanced losses or noises; instead, it can generate and manipulate one‐way EPR steering solely by adjusting the detuning between the magnon mode and the microwave drive field. It is also analyzed that the robustness of the entanglement and EPR steering against the dissipation of magnon and environmental temperature. The present scheme may provide a promising platform and an efficient quantum resource for quantum information processing.
We propose a scheme for generating and controlling remote nonreciprocal magnon--magnon entanglement in a cavity magnonic system with coherent feedback.The two microwave cavities are driven by independent single-mode squeezed vacuum fields, with a rotating YIG sphere in the left cavity and a stationary one in the right cavity. For a fixed rotation direction, reversing the bias magnetic field applied to the rotating sphere changes the sign of the Barnett shift, leading to nonreciprocal magnon--magnon entanglement. By tuning the cavity detuning and feedback phase, entanglement can be generated for one direction of the bias magnetic field while it vanishes for the opposite direction, yielding complete nonreciprocity. Coherent feedback enhances the entanglement at an appropriate reflectivity, whereas stronger feedback can reduce it. The relative squeezing phase provides additional control, and an appropriate choice of unequal squeezing factors improves the entanglement at fixed total input photon occupation. With the squeezed inputs kept fixed, moderate feedback also increases the critical temperature for magnon entanglement.Our results provide a controllable approach to preparing remote nonreciprocal quantum correlations in cavity magnonic systems.