Squeezing and Entanglement of Magnons in Ordered Magnetic Structures

Abstract

Magnon transport is a promising platform for future data processing and transmission. It does not rely on the transport of electrons and thus avoids joule heating, leading to more energy efficient processes. Essential devices like magnon transistors have been shown to work and a coupling to classical, electron based devices is possible using the spin Hall effect making magnons the ideal candidate for future data structures. Furthermore, two dimensional magnets have shown to be an essential building block in Van der Waals heterostructures which are a gateway to artificial materials with tailored properties. For these reasons a thorough understanding of the properties of magnons and their transport behaviour is of great importance. This dissertation focuses on the aspect of squeezing in different magnetic systems and its theoretical investigation. We find that in contrast to photonic systems squeezing is an inherent property of the eigenmodes of magnets and can be extremely large in systems like antiferromagnets where its origin lies in the exchange interaction. We further investigate the entanglement of magnons which accompanies their squeezing. We find that between two dimensional systems long range entanglement is possible for finite system sizes. The degree of entanglement inherited from squeezing is directly proportional to the degree of squeezing in the system making magnets the perfect tool to infuse entanglement into systems coupled to them. This is of interest in quantum computing where one relies on the entanglement of spin Qubits. In the final part of this thesis we find that the squeezing between modes is symmetric under wave vector inversion even if the energy dispersion is not. As a concrete example we investigated a non-collinear system, a so called spin spiral, and proved the symmetry of the squeezing parameter under wave vector inversion.