腔光子-自旋波量子耦合系统中各向异性奇异点的实验研究

通过耦合三维微波腔中光子和腔内钇铁石榴石单晶小球中的自旋波量子形成腔-自旋波量子的耦合系统,并通过精确调节系统参数在该实验系统中观测到各向异性奇异点.奇异点对应于非厄米系统中一种特殊状态,在奇异点处,耦合系统的本征值和本征矢均简并,并且往往伴随着非平庸的物理性质.以往大量研究主要集中在各向同性奇异点的范畴,它的特征是在系统参数空间中沿着不同参数坐标趋近该奇异点时具有相同的函数关系.在这篇文章中,主要介绍实验上在腔光子-自旋波量子耦合系统中通过调节系统的耦合强度和腔的耗散衰减系数两条趋近奇异点的路径而实现了各向异性奇异点,具体分别对应于在趋近奇异点时,本征值的虚部的变化与耦合强度和腔的衰减系数的变化会有线性和平方根不同的行为.各向异性奇异点的实现有助于基于腔光子-自旋波量子耦合系统的量子信息处理和精密探测器件的进一步研究.

Observation of the anisotropic exceptional point in cavity magnonics system

We theoretically and experimentally demonstrate the anisotropic exceptional points(EPs)in the cavity magnonics system where magnons in a one millimeter-diameter yttrium iron garnet(YIG)sphere are coherently coupled with the microwave photons in a three-dimensional microwave cavity.The damping nature makes the cavity magnonics system inherently non-Hermitian.By solving the eigenvalues and eigenvectors of non-Hermitian Hamiltonian,a series of interesting and essential characteristics of the system can be obtained.Therefore,non-Hermitian physics has received more and more attention in both theory and experiment communities.Among them,exceptional points correspond to the non-Hermitian system’s degenerate states where the eigenvalues of the non-Hermitian system are identical,and the eigenvectors are parallel.The coupled cavity photon-magnon system has high tunability of coupling strength and cavity external damping rate,which is very suitable for studying EPs-related physics.Exceptional points(EPs)are crucial in all kinds of non-Hermitian physical systems,which have both fundamental and applicational importance.For instance,it can be used for sensitive detection by monitoring spectrum splitting of degenerate modes when a perturbation to be sensed occurs.The EPs can be anisotropic,which means that it has a different function relation when the system approaches the EPs along different parameter paths of the system.In this paper,by carefully designing the parameter space,we observe the anisotropic exceptional point in the coupled cavity photon-magnon system.It shows the linear and square-root behavior when the EPs are approached from different directions in the parameter space.One of the parameters is the position of the YIG sphere in the cavity,which determines the coherent coupling strength between the cavity mode and the magnon mode.Another parameter is the number of the gasket between the cavity signal loading port and the cavity external surface,which determines the external damping rate of the cavity mode.Both of these parameters can be easily and accurately adjusted experimentally.Our study paves the way for exploring anisotropic EPs based sensing technologies and more non-Hermitian related physics in the cavity magnonics system.