Abstract
The dynamics and thermal equilibrium of spin waves (magnons) in a quantum ferromagnet as well as the macroscopic magnetisation are investigated. Thermal noise due to an interaction with lattice phonons and the effects of spatial correlations in the noise are considered. We first present a Markovian master equation approach with analytical solutions for any homogeneous spatial correlation function of the noise. We find that spatially correlated noise increases the decay rate of magnons with low wave vectors to their thermal equilibrium, which also leads to a faster decay of the ferromagnet’s magnetisation to its steady-state value. For long correlation lengths and higher temperature we find that additionally there is a component of the magnetisation which decays very slowly, due to a reduced decay rate of fast magnons. This effect could be useful for fast and noise-protected quantum or classical information transfer and magnonics. We further compare ferromagnetic and antiferromagnetic behaviour in noisy environments and find qualitatively similar behaviour in Ohmic but fundamentally different behaviour in super-Ohmic environments.
Highlights
The investigation of spin waves and magnons has lead to the emerging field of magnonics [1,2,3] which aims to enable magnons as information carriers for both classical [4, 5] and quantum [6] information technology
We find that spatially correlated noise increases the decay rate of magnons with low wave vectors to their thermal equilibrium, which leads to a faster decay of the ferromagnet’s magnetisation to its steady-state value
We extend our model of the system of a ferromagnet to be an open quantum system, which allows us to model the interaction between the spins and the lattice phonons, which we will assume to be in a thermal equilibrium
Summary
Jan Jeske1,2,5 , Ángel Rivas3,4 , Muhammad H Ahmed, Miguel A Martin-Delgado and Jared H Cole.
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