Spin Waves: versatile, low-dissipation carriers in ferromagnetic systems as a potential source of entanglement

Spin Waves are the coherent oscillations of the magnetic moments of a medium, they do not involve any charge transfer and hence don’t cause Joule dissipation. Even if their fundamental properties are known since decades, their ultimate properties in complex nano-systems are even today a matter of intense investigation both in the theoretical and experimental territories. Their inherent propagation anisotropy is particularly appealing for applications, together with their easy tunability, which comes from Bragg diffraction across the nanostructures and can be controlled by either small magnetic fields or even voltage in multiferroic systems [1]. We review a few spin wave key properties, from a magnetized film, to a lattice of macrospins in an ice-like arrangement (artificial spin ice) and arrays of magnetic vortices. Their intrinsic wave nature, together with the quantization of their energy revealed by light scattering experiments, suggests to realize systems and conditions where spin waves occur as an entangled superposition of otherwise independent states. Following the exposure to tiny magnetic fields or anisotropies introduced in the material by external agents, the superposition breaks down into separate states correlated to the field or anisotropy values [2]. To illustrate the possibility, we discuss spin waves in the vortex state and hybrid spin waves in special ferromagnetic systems, in the perspective of computation and sensing [3]. [1] R. Negrello, F. Montoncello, M. T. Kaffash, M. B. Jungfleisch, and G. Gubbiotti, APL Mater. 10, 091115 (2022). [2] G. Gubbiotti, M. Madami, S. Tacchi, G. Carlotti, H. Tanigawa, T. Ono, L. Giovannini, F. Montoncello, and F. Nizzoli, Phys. Rev. Lett. 97, 247203 (2006). [3] Dany Lachance-Quirion, Yutaka Tabuchi, Arnaud Gloppe, Koji Usami, and Yasunobu Nakamura, Appl. Phys. Express 12, 070101 (2019).