Dynamics of quantum entanglement and Bell nonlocality in magnetic systems
Time: Mon 2024-06-10 09.15
Location: E3, Osquars backe 14, Stockholm
Language: English
Subject area: Physics, Theoretical Physics
Doctoral student: Yuefei Liu , Tillämpad fysik, Light and Matter Physics - Materials theory group
Opponent: Prof. Wolfgang Belzig,
Supervisor: Anna Delin, Tillämpad fysik; Prof. Erik Sjöqvist, ; Prof. Olle Eriksson, ; Vahid Azimi Mousolou,
QC 2024-05-23
Abstract
In this PhD thesis, the author first delves into the realm of quantum magnonics, focusing on the dynamics and properties of magnon modes and hybrid quantum models. The thesis introduce a comprehensive approach to studying both ferromagnetic and antiferromagnetic magnon systems using quantum mechanics tools, such as the second quantization of the spin Hamiltonian (Holstein-Primakoff transformation) and Bogoliubov transformation. This approach allows for the precise characterization of different coupling interactions, reflecting the symmetric properties of material lattice. Specifically, the author examines how these interactions enable the preparation of targeted isolated magnon (or boson) models, facilitating the control of vacuum and excited states. The thesis present a detailed analysis of the entanglement entropy of magnon modes in antiferromagnetic (AFM) materials , highlighting the role of exchange and Dzyaloshinskii-Moriya (DM) coupling terms. Moreover, the thesis propose a novel cavity magnonic setup that leverages the cavity photon degree of freedom for experimentally measuring entanglement in AFM magnon modes. Additionally, the thesis address the open system dynamics of magnon-magnon-phonon model in AFM lattice using the quantum Langevin equations. With the steady-state solution of quantum Langevin equations, one assess how external magnetic fields and temperature-dependent noise influence magnon-magnon entanglement in AFM lattice, leading to high-temperature entanglement in antiferromagnets under certain conditions.
Transitioning interest from magnons to magnetic spin systems, part of the thesis analyze the spin dynamics described by the Landau-Lifshitz equations under the quantum framework, that is explore the implications of the Landau-Lifshitz equations for quantum dynamics. The author and his colleagues propose a quantum analog of the Landau-Lifshitz-Gilbert equation as an effective equation for qubit dynamics, which has no intrinsic information loss (preserves the purity of quantum states) and is faster than classical Landau-Lifshitz-Gilbert spin dynamics. It offers a promising direction for further theoretical, computational and experimental investigation. The dynamics of quantum correlation in dimer systems are studied, providing insights into the behavior of both pure and mixed states.
This thesis not only advances our understanding of quantum entanglement and non-locality in quantum magnonics and spin dynamics but also sets the stage for future investigations into the quantum mechanical properties of novel materials and their applications in quantum information science. The methodologies and findings discussed here pave the way for developing more sophisticated quantum technologies and contribute to the broader field of quantum materials research.