Progress in studying entanglement and steering from the macroscopic view

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. Research Highlight .

January 2021 Vol. 64 No. 1: 210331 https://doi.org/10.1007/s11433-020-1622-x

Progress in studying entanglement and steering from the macroscopic view Ye Cao* School of Physics, Beijing Institute of Technology, Beijing 100081, China Received August 6, 2020; accepted September 18, 2020; published online November 27, 2020 Y. Cao, Progress in studying entanglement and steering from the macroscopic view, Sci. China-Phys. Mech. Astron. 64, 210331 (2021), https://doi.org/10.1007/s11433-020-1622-x

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Optical cavity modes

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Magnons, the collective excitation of magnetically ordered materials, have attracted considerable interest for their low energy consumption, long coherence time and useful working frequency from gigahertz to terahertz. Besides, magnons can coherently interact with phonons, microwave and optical photons, as well as superconducting qubits, as schematically depicted in Figure 1, providing a novel platform to achieve hybrid quantum systems [1]. Hybridizing distinct quantum systems with multitasking capabilities is critical in quantum information processing, because a single quantum system cannot keep pace with the fast development of quantum information and satisfy the requirement of building perfect quantum information networks [2]. The emergying field cavity spintronics has inspired many interesting physics like nonreciprocal microwave propagation and energy level attraction, together with quite a few applications such as magnon sensors and magnon-photon transducers. In docking cavity spintronics with quantum information science, an essential step is to understand the quantum correlation between magnons and photons in hybrid systems. Quantum entanglement, the most intrinsic feature of quantum mechanics, has found a variety of applications in quantum information processing. A strict subset of entanglement, Einstein-Podolsky-Rosen (EPR) steering provides extra security to various quantum information protocols that rely on entanglement. How to generate and enhance quantum entanglement between two modes, in particular between

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Mechanical modes Cavity magnomechanics

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Figure 1 (Color online) Hybrid quantum systems involving magnons. Magnons can be coupled with diverse quantum systems through different interaction types, which mainly consist of four different types. In optomagnonics (red), magneto-static modes can be coupled with optical cavity modes through the magneto-optical effects. While in the field of cavity electromagnonics (blue), magneto-static modes can be strongly coupled with microwave cavity modes via the magnetic dipole interaction within the strongcoupling regime even the ultrastrong-coupling regime. In the meanwhile, the strong interaction between magneto-static modes and qubits can be indirectly implemented with the assistance of the coupling bet