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### Antiferromagnetic cavity optomagnonics

#### Abstract

Currently there is a growing interest in studying the coherent interaction between magnetic systems and electromagnetic radiation in a cavity, prompted partly by possible applications in hybrid quantum systems. We propose a multimode cavity optomagnonic system based on antiferromagnetic insulators, where optical photons couple coherently to the two homogeneous magnon modes of the antiferromagnet. These have frequencies typically in the THz range, a regime so far mostly unexplored in the realm of coherent interactions, and which makes antiferromagnets attractive for quantum transduction from THz to optical frequencies. We derive the theoretical model for the coupled system, and show that it presents unique characteristics. In particular, if the antiferromagnet presents hard-axis magnetic anisotropy, the optomagnonic coupling can be tuned by a magnetic field applied along the easy axis. This allows us to bring a selected magnon mode into and out of a dark mode, providing an alternative for a quantum memory protocol. The dynamical features of the driven system present unusual behavior due to optically induced magnon-magnon interactions, including regions of magnon heating for a red-detuned driving laser. The multimode character of the system is evident in a substructure of the optomagnonically induced transparency window.

• Accepted 8 April 2020

DOI:https://doi.org/10.1103/PhysRevResearch.2.022027

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. Open access publication funded by the Max Planck Society.

1. Physical Systems
Atomic, Molecular & OpticalCondensed Matter & Materials Physics

#### Authors & Affiliations

• Max Planck Institute for the Science of Light, Staudtstrasse 2, PLZ 91058 Erlangen, Germany

• Max Planck Institute for the Science of Light, Staudtstrasse 2, PLZ 91058 Erlangen, Germany and Institute for Theoretical Physics, University Erlangen-Nürnberg, Staudtstrasse 7, 91058 Erlangen, Germany

• *tahereh.parvini@mpl.mpg.de
• victor.bittencourt@mpl.mpg.de
• silvia.viola-kusminskiy@mpl.mpg.de

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#### References

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Vol. 2, Iss. 2 — May - July 2020

##### Subject Areas

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#### Images

• ###### Figure 1

(a) Schematics of the antiferromagnetic optomagnonic cavity. The homogeneous magnon modes $\stackrel{̂}{\alpha }$ and $\stackrel{̂}{\beta }$ with frequencies ${\omega }_{\alpha ,\beta }$ and decay rates ${\mathrm{\Gamma }}_{\alpha ,\beta }$ couple to a cavity mode $\stackrel{̂}{c}$ with frequency ${\omega }_{c}$ and decay rate $\kappa$. (b) Pump-probe scheme: , magnon, optical cavity resonance, drive, and probe frequencies, respectively. The detuning of the drive is $\mathrm{\Delta }={\omega }_{d}-{\omega }_{c}$, and $\omega ={\omega }_{p}-{\omega }_{d}$.

• ###### Figure 2

Reduced optomagnonic coupling coefficients ${g}_{\alpha }$ and ${g}_{\beta }$, as a function of external bias magnetic field (as ${\omega }_{H}/{\omega }_{E}$) and of the magneto-optical asymmetry $K$. (a) Hard-axis dominated regime (${\omega }_{\perp }>{\omega }_{\parallel }$), ($\mathrm{NiO}$ [71]). (b) Easy-axis dominated regime (${\omega }_{\parallel }>{\omega }_{\perp }$), .

• ###### Figure 3

(a) Effective linewidth (left) and frequency shift (right) of the magnon modes vs detuning $\mathrm{\Delta }/{\omega }_{\alpha }$ for near-degenerate modes and (inset) well-separated modes. The highlighted area indicates an unusual amplification region in the red-detuned regime. (b) Frequency scheme for near-degenerate and well-separated frequencies. The red arrow indicates indirect magnon-magnon interactions, more relevant in the near-degenerate case. Parameters for ${\mathrm{MnF}}_{2}$ and for the main figures and ${\omega }_{H}/{\omega }_{E}=3.2×{10}^{-2}$ for the inset.

• ###### Figure 4

Reflection spectra for a red-detuned control laser as a function of the probe-pump detuning $\omega$ for a material with (a) degenerate magnon modes at zero magnetic field and (b) nondegenerate modes. Parameters: THz, $\mathrm{\Gamma }=1.5×{10}^{-3}$ THz, (a) parameters for ${\mathrm{MnF}}_{2}$ and $G\sqrt{{n}_{c}}/{\omega }_{E}=4.0×{10}^{-3}$, and (b) parameters for NiO and $G\sqrt{{n}_{c}}/{\omega }_{E}=1.8×{10}^{-3}$.

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