Perfect one-way steering in a non-Hermitian cavity magnonic system

The knowledge on quantum entanglement and one-way steering are crucial for quantum communication networks. We propose to generate perfect one-way steering with strong entanglement by the cooperative effect of coherent coupling and dissipative coupling in open cavity magnonics.
Perfect one-way steering in a non-Hermitian cavity magnonic system
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As a frontier subject of quantum mechanics and informatics, quantum information science is based on the basic principles of quantum mechanics, and has carried out research work in the field of the basic quantum information science and optical communication. With the development of quantum information, we gradually have a deeper understanding of quantum correlation.

Quantum nonlocality is an important quantum correlation and one of the most prominent features that distinguish the quantum theory from the classical physics. It serves as the central resource in quantum information processing. Quantum nonlocality manifests itself in three forms: quantum entanglement, quantum steering and Bell nonlocality, which are listed in a hierarchical order that the former covers the later ones. Quantum entanglement is an important physical resource in quantum key distribution, teleportation, quantum computing and other applications. Quantum steering as a special quantum correlation between quantum entanglement and Bell nonlocality allows one party, Alice, to change (i.e., to “steer”) the state of a distant party, Bob, by exploiting their shared entanglement. Quantum steering plays an important role in quantum communication networks because of fascinating asymmetry.Quantum steering can be achieved in various systems such as optomechanical systems, atom-mechanical systems, antiferromagnetic systems and so on. However, implementing a flexible and controllable one-way steering with strong entanglement is still a tricky issue, especially in the situation of lack of experimental resources. Great success has been made in the generation of asymmetric quantum steering during the past decades, but the essence of them is add asymmetric losses or noises to subsystems at the cost of reducing steerability, as well as the systems under studies are generally more complex. Researchers have been exploring whether it is possible to avoid such problems and achieve flexible and controllable one-way steering with strong entanglement in emerging fields.

Energy-level anti-crossing in the dissipative mechanism induced by coherent coupling.

Quantum correlations results.

Inspired by the above, the approach proposed in our work is based on the cooperative effect of coherent coupling and dissipative coupling in a non-Hermitian cavity magnonic system. We demonstrate that the maximum quantum entanglement and perfect one-way steering between photon and magnon modes can be obtained at two exceptional points-like in the eigenvalue energy spectrums of the Hamiltonian under the coexistence of coherent coupling and dissipative coupling. Furthermore, the quantum correlations in our work come from the quantum interference between the two coupling ways inside the non-Hermitian system, which is different from the previous studies  relying on nonlinear effects, such as optomechanical interaction, Kerr nonlinearity, squeezed light, and more. It can be seen from quantum correlations in our work has the following advantages: (i) the open cavity magnonic system has very flexible controllability; (ii) the generation of one-way steering adds no asymmetric losses or noises to the subsystems at the cost of reducing steerability, the steering directivity can be controlled by the relative phase of the cooperative dissipation and the frequency detuning of the magnon mode; (iii) the quantum entanglement and one- way steering can be achieved under both weak and strong coherent coupling mechanisms, and they are quite robust to the system dissipations and environment temperature.

The above description shows that our work may promote the understanding of asymmetric quantum correlation behavior in open cavity magnonic system, which has potential applications in semisided device-independent quantum key distribution, quantum secret sharing, one-way quantum computing, subchannel discrimination, etc. In addition, our work makes the generation of quantum entanglement and one-way steering an easier task!

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