Theory of Quantum Acoustomagnonics and Acoustomechanics with a Micromagnet

TL;DR

This paper develops a comprehensive quantum theory of acoustomagnonic interactions in micromagnets, extending previous work by deriving coupling rates, Hamiltonians, and analyzing higher order acoustic modes for cooling and probing center-of-mass motion.

Contribution

It provides the full quantum theoretical framework and analytical calculations for magnon-phonon coupling in small micromagnets, including higher order acoustic modes.

Findings

Calculated magnon-phonon coupling rates.

Derived the full acoustomechanical Hamiltonian.

Showed cooling of center-of-mass motion with multiple acoustic modes.

Abstract

Recently [1], we proposed a new way to engineer a flexible acoustomechanical coupling between the center-of-mass motion of an isolated micromagnet and one of its internal acoustic phonons by using a magnon as a passive mediator. In our approach, the coupling is enabled by the strong magnetoelastic interaction between magnons and acoustic phonons which originates from the small particle size. Here, we substantially extend our previous work. First, we provide the full theory of the quantum acoustomagnonic interaction in small micromagnets and analytically calculate the magnon-phonon coupling rates. Second, we fully derive the acoustomechanical Hamiltonian presented in Ref. [1]. Finally, we extend our previous results for the fundamental acoustic mode to higher order modes. Specifically, we show the cooling of the center-of-mass motion with a range of internal acoustic modes. Additionally, we derive the power spectral densities of the center-of-mass motion which allow to probe the same acoustic modes.