Research Of The Optomagnonics In Ferromagnetic Microcavity

In the past few decades,quantum technology based on quantum physics has made great progress including quantum computing,quantum simulation,quantum communi-cation,and quantum sensing.In particular,the hybrid quantum system which combines with different physical properties of the system to get better than a single physical sys-tem has attracted great interest.Among them,the hybrid quantum system based on the spin wave in ferromagnetic materials has attracted great attention.Spin waves are the collective excitations of magnetization in magnetically ordered materials.The magnon,quanta of the spin wave,can interact with microwave photon,optical photon,phonon,superconducting qubit,forming new platforms include cavity optomagnonics based on the magneto-optical effect,cavity magnomechanics based on magnetostrictive effect,quantum magnonics based on magnetic dipole interaction.And the frequency conver-sion from microwave to the optical photon,the measurement of a single magnon,and the magnon-phonon conversion are realized.Nowadays,quantum information technology based on the solid-state qubits is lim-ited by low temperature and microwave photons,which cannot achieve long-distance communications between qubits.Thus frequency conversion between microwave pho-ton and the optical photon has attracted great interest.Unlike microwave photons,the optical photon can transmit via optical fibers,making them suitable for long-distance communication.Besides,the optical domain provides a large number of well-developed quantum optical tools,such as efficient single-photon detectors and long lifetime quan-tum memories.Thus,the frequency conversion between microwave photon and opti-cal photon can realize the quantum communication between multiple qubits,and con-struct a hybrid quantum network.At present,frequency conversion has been realized in many systems,such as cavity optomechanical system,electro-optical interaction sys-tem,atomic system,cavity optomagnonics system,and so on.Among these systems,the cavity optomagnonics system has attracted much attention due to its long lifetime and tunability of the magnon.Although the frequency conversion from microwave to optical photon is realized in this system,the current conversion efficiency is very low,which requires further research to enhance efficiency.Here,we mainly focus on the cavity optomagnonics and has realized the non-reciprocal transmission based on the spin orbit coupling of the light,and the frequency conversion based on cavity optomagnonics,the main contents include:(1)The cavity optomagnonics in YIG microsphere is analyzed,by applying a static magnetic field in different directions and the optomagnonics can be divided into degen-erate three-wave mixing and non-degenerate three-wave mixing.Also,the selection rule of the above process is summarized.Besides,the efficiency of the conversion be-tween microwave and optical wave under two conditions is analyzed-It is found that the two conditions have their advantages.For the magnetic field parallel to the light path,the degenerate three-wave mixing condition is easily satisfied:it is not necessary to find two optical modes with a frequency difference of a magnon.For the magnetic field perpendicular to the optical path,the non-degenerate three-wave mixing has a large coupling strength and a large conversion efficiency.(2)The thermal bistability of magnons in yttrium iron garnet microspheres are ex-perimentally characterized.As the frequency of the microwave pump sweeps over the magnon frequency(gradually increasing or decreasing),the resonant wavelength shift of the optical mode in the microcavity presents an inconsistent change,similar to the thermal bistability in the microcavity with high quality factor.Because of the high qual-ity factor of the optical mode,the measurement sensitivity can be improved.And it is further found that the temperature change also induces the magnon frequency shift and the frequency shift depends on the crystal axis direction of the material.With some ap-propriate alignment of the magnetic field and the microsphere,the magnon frequency shift induced by the thermal bistability can be suppressed.Our results show its potential use in future experiments on magnon-based transducers.(3)Non-reciprocal light transmission is demonstrated in high-quality factor yttrium iron garnet microspheres via photonic spin orbit coupling and the Faraday effect.By ap-plying a magnetic field in the vertical direction of the resonator equator,the degeneracy of the clockwise and counter-clockwise whispering gallery modes is lifted,which illus-trates the non-reciprocal frequency shift of the WGM.The experimental results show that the higher-order azimuth angle and larger microsphere size is,the larger frequency separation will be observed.We observed as high as 0.69 GHz frequency separation in the YIG microsphere,which close to the optical linewidth and may be potential to realize broadband non-reciprocal photonic devices.(4)The frequency conversion between microwave and the optical photon has been realized in YIG microsphere.By applying a magnetic field parallel to the resonator equator,the intra-cavity field will be modulated when the magnon is excited,leading to magnetic Stokes and Anti-Stokes scattering,and the sideband signals can be observed.Besides we realized the energy conversion efficiency of 3.62×10-6.Furthermore,due to the tunability of the magnon,the frequency conversion under the magnon frequency of 3.5GHz-6GHz was realized in the experiment.Our results provide a microwave-to-photon transducer that operates over a wide bandwidth,revealing potential applications in hybrid quantum systems.