主讲人：白凯 博士（武汉大学）

题目：Nonlinear Exceptional Points with a Complete Basis in Dynamics

时间：2023年07月21日（周五）下午15：00

地点：理工楼1201报告厅

联系人：钟寅

报告摘要：

Exceptional points (EPs) are algebraic singularities at which two or more eigenvalues and their corresponding eigenvectors, simultaneously coalesce. The singular spectral offers opportunities for ultrasensitive measurements, mode discrimination, etc [1,2]. Meanwhile, chiral state transfer due to EPs provides attractive schemes for topological energy transfer, polarization state conversion, etc. However, in conventional wisdom, the coalescence of eigenvectors inevitably leads to the loss of completeness of eigenbasis, which triggers divergent noise effects and hinders the corresponding key applications. Therefore, can the completeness of eigenbasis be revived while the key features of EPs are still preserved? Previous studies mainly focused on linear systems, where the gain and loss have fixed values independent of the fields' amplitudes. A proper description of gain elements involves nonlinear effects. Exploring the nonlinearity of saturable gain [3], we demonstrate a nonlinear 5th-order EP (NEP₅) with both theory and circuit simulation in three coupled resonators. At the NEP₅, one stable and another four auxiliary self-consistent eigenstates of the nonlinear Hamiltonian coalesce. Meanwhile, the spectra singularity and the chiral state transfer also present. Intriguingly, the eigenbasis of the instantaneous Hamiltonian which governs the system’s dynamics is still complete [4]. As a direct consequence, noise is greatly suppressed from a fundamental aspect. Moreover, compared with conventionally Eps, the chiral states transfer herein survives for a much smaller circling path, which thus enables the miniaturization of various key applications based on chiral states transfer.

参考文献：

[1]W. Chen, et al. , Nature 548, 192 (2017).

[2]H. Hodaei, et al., Nature 548, 187 (2017).

[3]K. Bai, et al., Natl. Sci. Rev. 10, (2023).

[4]K. Bai, et al., Phys. Rev. Lett. 130, 266901 (2023).

个人简介：

白凯博士2015年本科毕业于兰州大学物理科学与技术学院。同年，进入兰州大学物理科学与技术学院跟随罗洪刚教授和安钧鸿教授学习研究量子计量，并于2019年硕士毕业。随后，他在武汉大学肖孟教授课题组学习研究非线性非厄米奇异结构，并于2023年获得博士学位。目前已进入武汉大学刘正猷教授课题组从事博士后工作，他将继续学习研究非线性非厄米物理。