Wave Transport in Complex Systems Lab, Department of Physics, Wesleyan University, Middletown, CT, USA.
Department of Engineering Physics, University of Wisconsin-Madison, Madison, WI, USA.
Nature. 2022 Jul;607(7920):697-702. doi: 10.1038/s41586-022-04904-w. Epub 2022 Jul 27.
Exceptional points (EP) are non-Hermitian degeneracies where eigenvalues and their corresponding eigenvectors coalesce. Recently, EPs have attracted attention as a means to enhance the responsivity of sensors, through the abrupt resonant detuning occurring in their proximity. In many cases, however, the EP implementation is accompanied by noise enhancement, leading to the degradation of the sensor's performance. The excess noise can be of fundamental nature (owing to the eigenbasis collapse) or of technical nature associated with the amplification mechanisms utilized for the realization of EPs. Here we show, using an EP-based parity-time symmetric electromechanical accelerometer, that the enhanced technical noise can be surpassed by the enhanced responsivity to applied accelerations. The noise owing to eigenbasis collapse is mitigated by exploiting the detuning from a transmission peak degeneracy (TPD) - which forms when the sensor is weakly coupled to transmission lines - as a measure of the sensitivity. These TPDs occur at a frequency and control parameters for which the biorthogonal eigenbasis is still complete and are distinct from the EPs of the parity-time symmetric sensor. Our device shows a threefold signal-to-noise-ratio enhancement compared with configurations for which the system operates away from the TPD.
异常点（EP）是非厄米简并，其中特征值及其对应的特征向量合并。最近，EP 作为一种增强传感器响应度的手段引起了人们的关注，这是由于它们附近发生的突然共振失谐。然而，在许多情况下，EP 的实现伴随着噪声增强，导致传感器性能下降。额外的噪声可能具有根本性（由于特征基崩溃），也可能与为实现 EP 而利用的放大机制有关。在这里，我们使用基于 EP 的奇偶时间对称机电加速度计表明，增强的技术噪声可以被增强的加速度响应所超越。通过利用从传输峰简并（TPD）的失谐来减轻由于特征基崩溃引起的噪声，当传感器与传输线弱耦合时会形成 TPD，它可以作为灵敏度的一种度量。这些 TPD 出现在频率和控制参数处，在这些频率和控制参数下，双正交特征基仍然是完整的，并且与奇偶时间对称传感器的 EP 不同。与系统远离 TPD 运行的配置相比，我们的设备显示出三倍的信噪比增强。
