Abstract
Quantum magnonics is an emerging research field, with great potential for applications in magnon based hybrid systems and quantum information processing. Quantum correlation, such as entanglement, is a central resource in many quantum information protocols that naturally comes about in any study toward quantum technologies. This applies also to quantum magnonics. Here, we investigate antiferromagnetic coupling of two ferromagnetic sublattices that can have two different magnon modes. We show how this may lead to experimentally measurable bipartite continuous-variable magnon-magnon entanglement. The entanglement can be fully characterized via a single squeezing parameter or, equivalently, entanglement parameter. The clear relation between the entanglement parameter and the Einstein, Podolsky, and Rosen (EPR) function of the ground state opens up for experimental quantification magnon-magnon continuous-variable entanglement and EPR nonlocality. We propose a practical experimental realization to measure the EPR function of the ground state, in a setting that relies on magnon-photon interaction in a microwave cavity.
Highlights
Hybrid quantum systems provide a natural flexible platform for quantum technologies
We propose a practical experimental realization to measure the EPR function of the ground state, in a setting that relies on magnon-photon interaction in a microwave cavity
The measurement setup is based on magnon-photon coupling in a microwave cavity, which is appropriate for a wide range of antiferromagnetic materials [13] or synthetic antiferromagnetic multilayers [14]
Summary
Hybrid quantum systems provide a natural flexible platform for quantum technologies. Recent developments in quantum magnon spintronics suggest that hybrid quantum systems based on collective spin-wave excitations in magnetic materials, i.e., magnons, are highly promising for many short and long term applications in quantum technologies, including quantum sensing, quantum communication, quantum simulation, and quantum computing [1,2,3,4]. To the development of modern synthetic routes that allow most combinations of elements to form a magnetic material with tailored properties. This development in materials growth, in combination with advanced lithographic techniques for nanostructuring, open up new vistas to be explored in magnetic nanotechnology [12], where magnon-magnon entanglement is an essentially unexplored research field. We discuss how an antiferromagnetic coupling between two ferromagnetic spin lattices creates bipartite continuous-variable entanglement between the two ferromagnetic magnon modes in a way that each energy eigenstate of the system becomes a two-mode coherent state with nonzero entropy of entanglement. The measurement setup is based on magnon-photon coupling in a microwave cavity, which is appropriate for a wide range of antiferromagnetic materials [13] or synthetic antiferromagnetic multilayers [14]. Antiferromagnetic coupling between the layers are plentiful in the literature, and form the basis for the giant magnetoresistance effect [17]
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