2 research outputs found
Switching the Magnetization in Quantum Antiferromagnets
The orientation of the order parameter of quantum magnets can be used to
store information in a dense and efficient way. Switching this order parameter
corresponds to writing data. To understand how this can be done, we study a
precessional reorientation of the sublattice magnetization in an (an)isotropic
quantum antiferromagnet induced by an applied magnetic field. We use a
description including the leading quantum and thermal fluctuations, namely
Schwinger boson mean-field theory, because this theory allows us to describe
both ordered phases and the phases in between them, as is crucial for
switching. An activation energy has to be overcome requiring a minimum applied
field which is given essentially by the spin gap. It can be
reduced significantly for temperatures approaching the N\'eel temperature
facilitating switching. The time required for switching diverges when the field
approaches which is the signature of an inertia in the
magnetization dynamics. The temporal evolution of the magnetization and of the
energy reveals signs of dephasing. The switched state has lost a part of its
coherence because the magnetic modes do not evolve in phase.Comment: 19 pages, 20 figure
Truncated Wigner approximation for the bosonic model of large spin baths
The central spin model has a wide applicability, it is ideally suited to
describe a small quantum system, for instance a quantum bit, in contact to a
bath of spins, e.g., nuclear spins, or other small quantum systems in general.
According to previous work~[R\"ohrig \textit{et al.}, Phys. Rev. B {\bf 97},
165431 (2018)], a large bath of quantum spins can be described as a bath of
quantum harmonic oscillators. But the resulting quantum model is still far from
being straightforward solvable. Hence we consider a chain representation for
the bosonic degrees of freedom to study how well a truncated Wigner
approximation of the effective model of harmonic oscillators works in
comparison with other approximate and exact methods. Numerically, we examine
the effect of the number of bath spins and of the truncation level, i.e., the
chain length.Comment: 10 pages, 7 figure