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Journal of the Optical Society of America B

Enhancement of quantum correlations in a cavity–magnon system with feedback control

Si-Yu Qin, Xuanxuan Xin, Shi-Wen He, Chong Li

Published Nov 2, 2021• 8 citations
Publisher

Abstract

We propose a scheme to generate and enhance the quantum correlations between two magnons separated in two microwave cavities with feedback control of the cavity field. In each cavity, the magnon is coupled to the cavity mode by magnetic dipole interaction, and the interaction between two microwave cavities is realized via linear beam splitter interaction without any nonlinear interaction in the system. We show that the quantum entanglement, as a special quantum correlation, between the two magnons is improved in the system with double-feedback control, and the entanglement is highly robust to temperature. It is always possible to optimize the entanglement by modulating the gain of the other feedback loop if the parameters of one of the feedback loops are given. Also, there is one-way steering between two magnons of the system in the presence of a single feedback loop.

DOI
10.1364/josab.442375

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We propose a scheme to generate and enhance the quantum correlations between two magnons separated in two microwave cavities with feedback control of the cavity field. In each cavity, the magnon is coupled to the cavity mode by magnetic dipole interaction, and the interaction between two microwave cavities is realized via linear beam splitter interaction without any nonlinear interaction in the system. We show that the quantum entanglement, as a special quantum correlation, between the two magnons is improved in the system with double-feedback control, and the entanglement is highly robust to temperature. It is always possible to optimize the entanglement by modulating the gain of the other feedback loop if the parameters of one of the feedback loops are given. Also, there is one-way steering between two magnons of the system in the presence of a single feedback loop.
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 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 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.
We present an alternative scheme to generate genuine tripartite entanglement and steering among one photon and two magnons in a cavity magnonical system, where two yttrium iron garnet spheres are respectively placed inside two microwave cavities driven by a two-mode squeezed field and subjected to homodyne-measurement feedback. It is found that quantum feedback on two cavities plays a crucial role in enhancing quantum correlations of photons and magnons. In the absence of measurement feedback, only bipartite entanglement between two magnons is existent. In contrast, when the continuous measurement feedback is present, two magnons are strongly entangled and magnon–photon entanglement also appears. More importantly, the stable genuine magnon–photon–magnon tripartite entanglement and steering could be obtained based on the homodyne-measurement feedback on two microwave cavities, which are robust against the thermal fluctuations. The work we present provides a feasible way to manipulate the multipartite quantum correlations including entanglement and steering in hybrid quantum systems.
Cavity magnonics, owing to its strong magnon-photon coupling and excellent tunability, has attracted significant interest in quantum information science. However, achieving strong and robust macroscopic entanglement remains a long-standing challenge due to the inherently linear nature of the beam-splitter interaction. Here, we propose an experimentally feasible scheme to generate and enhance macroscopic entanglement between two remote magnon modes by injecting squeezed vacuum fields (SVFs) into coupled microwave cavities. We demonstrate that even a single SVF applied to one cavity can induce steady magnon-magnon entanglement, while applying two SVFs (the double-squeezed configuration) enables selective activation of two independent entanglement channels associated with the cavity supermodes. Remarkably, quantum interference between the two SVFs allows for phase-controlled enhancement of entanglement, resulting in significantly improved robustness against cavity dissipation and thermal noise. Under realistic parameters, the survival temperature of quantum entanglement increases from approximately 260260260 mK to 450450450 mK. Our results establish a versatile and controllable approach to generating and enhancing quantum entanglement through quantum interference between squeezed vacuum fields.
Abstract Quantum correlations (QCs) are widely recognized as crucial resources for a broad array of quantum information protocols. This underscores the pressing need for advanced methods to generate them efficiently. As a result, prioritizing the production and enhancement of these correlations within physical quantum hardware becomes essential. Here, we propose a scheme to analyze the influence of feedback on the entanglement and quantum steering between two magnonic modes in a dual-cavity system, with each magnon mode placed in a separate microwave cavity. We demonstrate that a significant increase in entanglement and quantum steering between the two magnon modes can be achieved by introducing feedback. In addition, the feedback also enhances the thermal resistance of the system, as QCs survive at temperatures where they would otherwise disappear in the absence of feedback. Moreover, we show that QCs reach their peak when both the cavity and magnon modes are in resonance within each separate cavity. Additionally, the entanglement is found to increase with the squeezing parameter of the input light, eventually reaching a plateau where it remains constant.