The non-Hermitian system, which is coupled with the external environment, differs significantly from the Hermitian system in terms of physical properties. EPs are special degenerate points of spectra that exist in the non-Hermitian system. Physical effects and applications related to EPs have attracted wide attention on topics such as asymmetric mode conversion, single-mode lasers, and their high-sensitivity sensing capability based on Nth-order mode splitting near the EPs. However, studies to date have focused primarily on optical EPs. Phenomena and applications related to EPs in other physical systems are still expected to be explored further. As mechanical modes can be easily coupled with many physical quantities, a multiphysics system built upon this foundation will allow a higher degree of freedom for the study of EPs. In addition, with regard to ultrasensitive sensing, mechanical EPs have shown greater potentials in application. However, gigahertz mechanical EPs on chips have remained elusive due to great challenges in the manipulation of the high frequency mechanical modes.

Ph.D. candidate Ning Wu proposed a tunable mechanical non-Hermitian system with optomechanical zipper cavity. By tailoring the interaction between two mechanical modes through the optical field, our team demonstrated anti-parity-time-symmetry mechanical EPs in on-chip systems for the first time, and published this breakthrough on Science Advances. This study provides an integrated on-chip platform for investigating the related physics of mechanical EPs, such as non-Hermitian phenomena, nonlinear effects, and phononic topology. It also suggests possible solutions to technical obstacles in applications such as ultrasensitive sensing and precision measurement of physical quantities.

The corresponding authors of this paper include Professor Yidong Huang and Associate Professor Kaiyu Cui, who also shares the first authorship with Ning Wu, a PhD student from the Class of 2018. The study was funded by a number of programs, including the National Key R&D Program of China and the National Natural Science Foundation of China.

Access full-text paper at https://www.science.org/doi/10.1126/sciadv.abp8892