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Applications and Significance of Magneto-Optical Garnets in Quantum Computing and the Quantum Internet

Mehmet Keçeci

Published Oct 12, 2026• 0 citations

Abstract

Applications and Significance of Magneto-Optical Garnets in Quantum Computing and the Quantum Internet Mehmet Keçeci Orcid: https://orcid.org/0000-0001-9937-9839 Abstract: Magneto-optical garnets, and in particular yttrium iron garnet (YIG, Y₃Fe₅O₁₂), have emerged as a critical interface material in quantum information processing technologies. Superconducting qubits typically operate with microwave photons in the gigahertz regime, whereas long-distance quantum communication relies on visible or near-infrared photons propagating through optical fibres. The ability to coherently link these two fundamentally different physical platforms constitutes a prerequisite for scalable quantum computing architectures and a global quantum internet. Owing to their exceptionally low magnetic damping, high spin density, optical transparency in the near-infrared window, and pronounced Faraday effect, YIG and related garnet compounds provide a versatile hybrid platform that supports coherent quantum state transfer among microwave photons, optical photons, phonons, and superconducting qubits. In this work we review the fundamental physical properties of magneto-optical garnets, their roles in quantum magnonics and optomagnonics, their potential for microwave-to-optical quantum transduction, their functionality in optical isolation and nonreciprocal photonic devices, and the principal technological limitations that currently constrain their performance. We further assess the strategic significance of these materials for distributed quantum computing and quantum internet architectures. Keywords: magneto-optical, garnet, YIG, quantum magnonics, quantum transduction, quantum internet, superconductingqubit, optical isolator, nanostructures, yttrium.

DOI: 10.5281/zenodo.23308278

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Applications and Significance of Magneto-Optical Garnets in Quantum Computing and the Quantum Internet Mehmet Keçeci Orcid: https://orcid.org/0000-0001-9937-9839 Abstract: Magneto-optical garnets, and in particular yttrium iron garnet (YIG, Y₃Fe₅O₁₂), have emerged as a critical interface material in quantum information processing technologies. Superconducting qubits typically operate with microwave photons in the gigahertz regime, whereas long-distance quantum communication relies on visible or near-infrared photons propagating through optical fibres. The ability to coherently link these two fundamentally different physical platforms constitutes a prerequisite for scalable quantum computing architectures and a global quantum internet. Owing to their exceptionally low magnetic damping, high spin density, optical transparency in the near-infrared window, and pronounced Faraday effect, YIG and related garnet compounds provide a versatile hybrid platform that supports coherent quantum state transfer among microwave photons, optical photons, phonons, and superconducting qubits. In this work we review the fundamental physical properties of magneto-optical garnets, their roles in quantum magnonics and optomagnonics, their potential for microwave-to-optical quantum transduction, their functionality in optical isolation and nonreciprocal photonic devices, and the principal technological limitations that currently constrain their performance. We further assess the strategic significance of these materials for distributed quantum computing and quantum internet architectures. Keywords: magneto-optical, garnet, YIG, quantum magnonics, quantum transduction, quantum internet, superconductingqubit, optical isolator, nanostructures, yttrium.

The development of scalable quantum networks requires coherent interfaces capable of converting microwave photons used in superconducting quantum processors into optical photons suitable for long-distance fiber transmission. This review surveys recent progress in microwave-to-optical quantum transduction across optomechanical, electro-optic, and magneto-optic platforms, with emphasis on conversion efficiency, bandwidth, added noise, and operating temperature. In addition to standard metrics, we propose the internal efficiency eta_in and the magnon decay rate kappa_m/2pi as normalized parameters that enable fairer comparison across heterogeneous implementations. Optomechanical systems achieve internal phonon-to-photon efficiencies of 93% with sub-quantum added noise of 0.25 quanta at millikelvin temperatures. Electro-optic devices based on LiNbO3 and AlN have advanced from room-temperature efficiencies below 1% to millikelvin systems with internal efficiencies approaching 99.5%, added noise as low as 0.16 quanta at 60 mK, and bandwidths extending to several tens of megahertz. Magneto-optic (optomagnonic) platforms exhibit the lowest efficiencies (typically

10^{-10}

to

10^{-8})

, but offer intrinsic non-reciprocity and broadband magnonic operation, with emerging approaches based on topological heterostructures and magnon squeezing predicting enhancements up to

10^{-4}

. Optomechanical systems appear promising for high-fidelity quantum state transfer, electro-optic transducers for high-bandwidth coherent links, and magneto-optic devices for non-reciprocal network components. We discuss the fundamental trade-off between efficiency and added noise across all three platforms, and argue that heterogeneous microwave-optical transduction is emerging as a key enabling technology for distributed quantum computing and large-scale quantum networks.

Realizing a strong light-matter interaction via magnetic dipoles is of fundamental importance in physics, and a cavity magnonics system has provided a unique platform to achieve strong and even ultrastrong light-matter interaction. In this work, transparency induced by magnon-photon interactions in cavity quantum electrodynamics (QED) system coupling a yttrium-iron-garnet (YIG,Y3Fe5O12) (YIG) sphere has been investigated. The spectral separation reveals a linear relationship with the coupling strength, which might find applications in magnon dark state and magnon-based quantum information processing.

Hybrid systems based on magnons in ferromagnetic materials, such as yttrium iron garnet, have achieved remarkable development in the last decade. These include the coupling of magnons to microwave and optical photons, superconducting qubits, phonons, spins, the center-of-mass motion of a ferromagnet, etc. Here, we review both the experimental and theoretical progress in this field, focusing on the generation of magnonic quantum states and their applications in a broad range of fields. Since the strong coupling is a prerequisite for achieving coherent quantum control of magnons and preparing magnonic quantum states, we start by introducing representative strong-coupling experiments in cavity magnonics, then review a series of protocols for creating various magnonic quantum states, such as Fock, cat, squeezed, and entangled states, and discuss their potential applications in macroscopic quantum studies, quantum information science, quantum sensing, magnonic quantum devices, dark matter detection, and so on. Finally, we summarize the review and give an outlook for the future study of quantum magnonics.

In this work, an approach based on the use of yttrium iron garnet (YIG) to increase the efficiency of quantum frequency conversion has been theoretically studied. YIG, which is a ferrimagnetic insulator transparent to both microwave and optical frequencies, has a very low damping parameter. Therefore, the coupling of YIG to microwave resonator modes is very strong. It has been demonstrated that it is possible to use the spin-wave oscillations of YIG to increase essentially the coupling of microwave photons to

\text{Er}^{3+}

spin-flip transitions. The basic parameters of 2 -stage microwave-to-optic transduction in the proposed Erbium-YIG-based Hybrid Quantum System have been theoretically analyzed. The conditions needed for efficient coupling between magnetic resonance levels of

\text{Er}^{3+}

ions and spin wave modes have been also considered.

Er-substituted yttrium iron garnet (Er:YIG) holds the potential of combining the low magnetic damping of YIG with the telecom-band optical transitions of

\text{Er}^{3+}

ions, making it a suitable material for hybrid optomagnonic devices and microwave-to-optical quantum transduction. We report the epitaxial growth of

\text{Er}_{x}\text{Y}_{3-x}\text{Fe}_{5}\text{O}_{12}

films with

x=0.008-0.20

on (111)-oriented gadolinium gallium garnet (GGG) substrates using pulsed laser deposition. X-ray diffraction, reciprocal space mapping, and scanning transmission electron microscopy confirm single-phase, fully coherent growth with atomically sharp interfaces across the entire substitution range. Magnetometry reveals a gradual decrease in saturation magnetization with increasing Er content, consistent with antiparallel coupling between Er

^{3+}

spins and the net Fe

^{3+}

moments, along with the emergence of an in-plane uniaxial magnetic anisotropy. The ferromagnetic resonance broadens with Er concentration due to increased Gilbert damping and inhomogeneous linewidth broadening. Films with low Er content (

x=0.008

), most relevant for optomagnonic applications, retain nearly isotropic magnetization and exhibit a damping parameter only slightly higher than that of undoped YIG. These results identify growth and substitution conditions that preserve YIG's low-loss magnetic properties while introducing optical functionality, establishing Er:YIG as a viable platform for hybrid quantum magnonics and microwave-to-optical transduction.

Abstract Coherent quantum transduction between microwave and optical signals is of great importance for long-distance quantum communication. Here we propose a novel scheme for the implementation of nonreciprocal single-photon state conversion between microwave and optical modes based on a hybrid magnonic system. A yttrium–iron–garnet (YIG) sphere with both the optomechanical and the optomagnetic properties is exploited to couple with a three-dimensional superconducting microwave resonator. The magnetostatic mode of the YIG sphere is treated as an intermediate to interact with the microwave and optical modes simultaneously. By manipulating the amplitudes and phase differences between the couplings via external driving fields, we show that the nonreciprocal microwave-light single-photon state conversion can be realized via the quantum interference effect.