We put forward the concept of an optomagnonic crystal: a periodically patterned structure at the microscale based on a magnetic dielectric, which can co-localize magnon and photon modes. The co-localization in small volumes can result in large values of the photon-magnon coupling at the single quanta level, which opens perspectives for quantum information processing and quantum conversion schemes with these systems. We study theoretically a simple geometry consisting of a one-dimensional array of holes with an abrupt defect, considering the ferrimagnet Yttrium Iron Garnet (YIG) as the basis material. We show that both magnon and photon modes can be localized at the defect, and use symmetry arguments to select an optimal pair of modes in order to maximize the coupling. We show that an optomagnonic coupling in the kHz range is achievable in this geometry, and discuss possible optimization routes in order to improve both coupling strengths and optical losses.
Recent studies show that hybrid quantum systems based on magnonics provide a new and promising platform for generating macroscopic quantum states involving a large number of spins. Here we show how to entangle two magnon modes in two massive yttrium-iron-garnet (YIG) spheres using cavity optomagnonics, where magnons couple to high-quality optical whispering gallery modes supported by the YIG sphere. The spheres can be as large as 1 mm in diameter and each sphere contains more than $10^{18}$ spins. The proposal is based on the asymmetry of the Stokes and anti-Stokes sidebands generated by the m…
Magnon as a quantized spin wave has attracted extensive attentions in various fields of physics, such as magnon spintronics, microwave photonics, and cavity quantum electrodynamics. Here, we explore theoretically magnon chaos-order transition in cavity optomagnonics, which is still remains largely unexplored in this emerging field. We find that the evolution of the magnon experiences the transition from order to period-doubling bifurcation and finally enter chaos by adjusting the microwave driving power. Different from the normal chaos, the magnon chaos-order transition proposed here is phase-…
Magnons in ferrimagnetic insulators such as yttrium iron garnet (YIG) have recently emerged as promising candidates for coherent information processing in microwave circuits. Here we demonstrate optical whispering gallery modes of a YIG sphere interrogated by a silicon nitride photonic waveguide, with quality factors approaching $10^6$ in the telecom c-band after surface treatments. Moreover, in contrast to conventional Faraday setup, this implementation allows input photon polarized colinearly to the magnetization to be scattered to a sideband mode of orthogonal polarization. This Brillouin s…
Single-mode high-index-contrast waveguides have been ubiquitously exploited in optical, microwave, and phononic structures for achieving enhanced wave-matter interactions. Although micro-scale optomechanical and electro-optical devices have been widely studied, optomagnonic devices remain a grand challenge at the microscale. Here, we introduce a planar optomagnonic waveguide platform based on a ferrimagnetic insulator that simultaneously supports single transverse mode of spin waves (magnons) and highly confined optical modes. The co-localization of spin and light waves gives rise to enhanced …
We show how to prepare a steady-state entangled state between magnons and optical photons in an opto-magnomechanical configuration, where a mechanical vibration mode couples to a magnon mode in a ferrimagnet by the dispersive magnetostrictive interaction, and to an optical cavity by the radiation pressure. We find that, by appropriately driving the magnon mode and the cavity to simultaneously activate the magnomechanical Stokes and the optomechanical anti-Stokes scattering, a stationary optomagnonic entangled state can be created. We further show that, by activating the magnomechanical state-s…
The polarization dependence of magnon-photon scattering in an optical microcavity is reported. Due to the short cavity length, the mode-matching conditions found in previously explored, large path-length whispering gallery resonators are absent. Nonetheless, for cross-polarized scattering a strong and broadband suppression of one side-band is observed. This arises due to an interference between the Faraday and second-order Cotton-Mouton effects. To fully account for the suppression of the cross-polarized scattering, it is necessary to consider the squeezing of magnon modes intrinsic to thin-fi…
In the emerging field of cavity optomagnonics, photons are coupled coherently to magnons in solid-state systems. These new systems are promising for implementing hybrid quantum technologies. Being able to prepare Fock states in such platforms is an essential step towards the implementation of quantum information schemes. We propose a magnon-heralding protocol to generate a magnon Fock state by detecting an optical cavity photon. Due to the peculiarities of the optomagnonic coupling, the protocol involves two distinct cavity photon modes. Solving the quantum Langevin equations of the coupled sy…
Cavity optomagnonics has emerged as a promising platform for studying coherent photon-spin interactions as well as tunable microwave-to-optical conversion. However, current implementation of cavity optomagnonics in ferrimagnetic crystals remains orders of magnitude larger in volume than state-of-the-art cavity optomechanical devices, resulting in very limited magneto-optical interaction strength. Here, we demonstrate a cavity optomagnonic device based on integrated waveguides and its application for microwave-to-optical conversion. By designing a ferrimagnetic rib waveguide to support multiple…
Inelastic scattering of photons is a promising technique to manipulate magnons but it suffers from weak intrinsic coupling. We theoretically discuss an idea to increase optomagnonic coupling in optical whispering gallery mode cavities, by generalizing previous analysis to include the exchange interaction. We predict that the optomagnonic coupling constant to surface magnons in yttrium iron garnet (YIG) spheres with radius $300\,\mathrmμ$m can be up to $40$ times larger than that to the macrospin Kittel mode. Whereas this enhancement falls short of the requirements for magnon manipulation in YI…
Reaching strong light-matter coupling in solid-state systems has been long pursued for the implementation of scalable quantum devices. Here, we put forward the concept of a platform capable of achieving strong coupling between magnetic excitations (magnons) and optics based in an epsilon-near-zero medium, that's it, a medium in which the permittivity is close to zero. We adopt a phenomenological approach to quantize the electromagnetic field inside a dispersive magnetic medium and obtain a Hamiltonian describing the interaction between photons and magnons and the frequency-dependent coupling. …
Combining the technologies of quantum optics and magnonics, we find that the circularly polarized laser can dynamically realize the quasiequilibrium magnon Bose-Einstein condensates (BEC). The Zeeman coupling between the laser and spins generates the optical Barnett field, and its direction is controllable by switching the laser chirality. We show that the optical Barnett field develops the total magnetization in insulating ferrimagnets with reversing the local magnetization, which leads to the quasiequilibrium magnon BEC. This laser-induced magnon BEC transition through optical Barnett effect…
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 T…
Combining advanced technologies of optics and antiferromagnetic spintronics, we present a method to realize ultrafast spin transport. The optical Barnett effect provokes quasiequilibrium Bose-Einstein condensates (BECs) of magnons associated with the fully spin-polarized state in insulating antiferromagnets (AFs). This optomagnonic Barnett effect enables us to exploit coherent magnons of high frequency over the conventional ones of (sub-) terahertz associated with the Néel magnetic order. We show that the macroscopic coherence of those optical magnon BECs induces a spin current across the junc…
Coherent conversion of photons to magnons, and back, provides a natural mechanism for rapid control of interactions between stationary spins with long coherence times and high-speed photons. Despite the large frequency difference between optical photons and magnons, coherent conversion can be achieved through a three-particle interaction between one magnon and two photons whose frequency difference is resonant with the magnon frequency, as in optomechanics with two photons and a phonon. The large spin density of a transparent ferromagnetic insulator (such as the ferrite yttrium iron garnet) in…
Achieving strong coupling between light and matter excitations in hybrid systems is a benchmark for the implementation of quantum technologies. We recently proposed [arXiv:2110.02984] that strong single-particle coupling between magnons and light can be realized in a magnetized epsilon-near-zero (ENZ) medium, in which magneto-optical effects are enhanced. Here we present a detailed derivation of the magnon-photon coupling Hamiltonian in dispersive media both for degenerate and non-degenerate optical modes, and show the enhancement of the coupling near the ENZ frequency. Moreover, we show that …
Optomagnonic systems, where light couples coherently to collective excitations in magnetically ordered solids, are currently of high interest due to their potential for quantum information processing platforms at the nanoscale. Efforts so far, both at the experimental and theoretical level, have focused on systems with a homogeneous magnetic background. A unique feature in optomagnonics is however the possibility of coupling light to spin excitations on top of magnetic textures. We propose a cavity-optomagnonic system with a non homogeneous magnetic ground state, namely a vortex in a magnetic …
A ferromagnetic sphere can support \textit{optical vortices} in forms of whispering gallery modes and \textit{magnetic quasi-vortices} in forms of magnetostatic modes with non-trivial spin textures. These vortices can be characterized by their orbital angular momenta. We experimentally investigate Brillouin scattering of photons in the whispering gallery modes by magnons in the magnetostatic modes, zeroing in on the exchange of the orbital angular momenta between the optical vortices and the magnetic quasi-vortices. We find that the conservation of the orbital angular momentum results in diffe…
Backscattering Raman spectroscopic investigations were performed on an yttrium-iron garnet single crystal using linearly and circularly polarized light. A terahertz (THz) magnon of the Kaplan-Kittel (KK) exchange resonance was discovered, which had been regarded as unobservable via optical methods. The KK exchange resonance had a 7.8-THz frequency at 80 K, and the polarization selection rule led to an antisymmetric Raman tensor of the $A_{2}$ mode. Moreover, the assignment of all the Raman-active phonon modes, $3A_{1g}$, $8E_{g}$, and $14T_{2g}$, was proposed. This study will stimulate further…
Experiments during the past two years have shown strong resonant photon-magnon coupling in microwave cavities, while coupling in the optical regime was demonstrated very recently for the first time. Unlike with microwaves, the coupling in optical cavities is parametric, akin to optomechanical systems. This line of research promises to evolve into a new field of optomagnonics, aimed at the coherent manipulation of elementary magnetic excitations by optical means. In this work we derive the microscopic optomagnonic Hamiltonian. In the linear regime the system reduces to the well-known optomechan…
Engineered quantum systems enabling novel capabilities for communication, computation, and sensing have blossomed in the last decade. Architectures benefiting from combining distinct and complementary physical quantum systems have emerged as promising platforms for developing quantum technologies. A new class of hybrid quantum systems based on collective spin excitations in ferromagnetic materials has led to the diverse set of experimental platforms which are outlined in this review article. The coherent interaction between microwave cavity modes and collective spin-wave modes is presented as …
We experimentally identify the magnetostatic modes active for Brillouin light scattering in the optical whispering gallery modes of a yttrium iron garnet sphere. Each mode is identified by magnetic field dispersion of ferromagnetic-resonance spectroscopy and coupling strength to the known field distribution of the microwave drive antenna. Our optical measurements confirm recent predictions that higher-order magnetostatic modes can also generate optical scattering, according to the selection rules derived from the axial symmetry. From this we summarize the selection rules for Brillouin light sc…
