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Annalen der Physik

Quantum Correlation Enhanced with Quantum Coherent Feedback Control in a Cavity‐magnon Hybrid System

Yue‐Han Lin, Ya‐Qin Lin, Zhi‐Ying Lin, Rong‐Can Yang, Hong‐Yu Liu

Published Aug 30, 2024• 2 citations
Publisher

Abstract

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.

DOI
10.1002/andp.202400221

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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 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.
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.
Abstract Quantum entanglement (QE) and quantum steering (QS) are of importance for quantum information processing and computation. Though there are several schemes proposed for their realization, how to increase their degrees encounters a great challenge. In the present manuscript, it is proposed to enhance steady QE and control Gaussian QS for two magnons using a two‐photon field acting on either magnon. The cavity‐magnetic hybrid system consists of a microwave cavity in which two identical Yttrium‐iron‐garnet spheres are placed and the cavity is driven by a Josephson parametric amplifier (JPA) so as to generate steady QE and control Gaussian QS for the two Kittel modes. Besides, a two‐photon driving field acting on either magnon in order to enhance the degree of QE and the ability of QS. The best condition to maximum entanglement and steering degrees for the two magnon modes at MHz and is found via the competitive relationship between the two‐photon driving and JPA. Furthermore, it is revealed that steering direction for the two magnons can be controlled not only by the ratio between the two photon‐magnon coupling parameters but also by the two‐photon driving field, making controllable steering direction become easier.