#### Abstract

Dynamical backaction resulting from radiation pressure forces in optomechanical systems has proven to be a versatile tool for manipulating mechanical vibrations. Notably, dynamical backaction has resulted in the cooling of a mechanical resonator to its ground state, driving phonon lasing, the generation of entangled states, and observation of the optical-spring effect. In certain magnetic materials, mechanical vibrations can interact with magnetic excitations (magnons) via the magnetostrictive interaction, resulting in an analogous magnon-induced dynamical backaction. In this article, we directly observe the impact of magnon-induced dynamical backaction on a spherical magnetic sample’s mechanical vibrations. Moreover, dynamical backaction effects play a crucial role in many recent theoretical proposals; thus, our work provides the foundation for future experimental work pursuing many of these theoretical proposals.

4 More- Received 15 April 2021
- Revised 7 June 2021
- Accepted 9 July 2021

DOI:https://doi.org/10.1103/PhysRevX.11.031053

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

#### Physics Subject Headings (PhySH)

#### Popular Summary

The field of cavity optomechanics leverages the close coupling of light to mechanical vibrations to provide a versatile platform for research into entanglement swapping, squeezed states, wavelength transduction, quantum memories, and much more. These all rely on so-called dynamical backaction, where the light acts on the mechanics. Cavity magnomechanics adds magnetic excitations called magnons to the mix, which are coupled simultaneously to photons and phonons. Here, we demonstrate the full suite of dynamical backaction effects in cavity magnomechanics.

For our experiments, we fashion a microwave cavity out of a block of copper. Our magnetic element is a yttrium iron garnet sphere, placed free to move in a narrow tube that is affixed inside the microwave cavity. By varying the magnetic field within the cavity and measuring the mechanical vibrations of the yttrium iron garnet sphere in its tube, we detect all backaction effects including cooling the system from room temperature to 65 K, driving the mechanics into phonon lasing, and dynamical control over the mechanical frequency, all using only photons for control.

Our study opens the possibility for many quantum applications in cavity magnomechanics, such as cooling to the quantum ground state, entanglement swapping, and quantum correlation thermometry.