Exceptional-point-locked PT-symmetric system for ultrasensitive displacement sensing via amplitude readout

PT-symmetric exceptional points (EPs) are singular points where both eigenvalues and eigenvectors become degenerate, and whose bifurcation characteristics have been utilized to design high-sensitivity sensing systems. In this Letter, an amplitude-readout EP-locked displacement sensing system with sensitivity beyond conventional frequency-based methods is proposed. We observed that when a PT-symmetric coupled-resonator reader operates at the EP, the amplitude variation in the gain resonator shows significantly higher sensitivity to LC sensor displacement than the frequency shifts. The amplitude change exhibits a linear dependence on κs, significantly simplifying system calibration and enabling more accurate displacement measurements compared to the nonlinear dependence. A printed circuit board-based circuit prototype is built to validate our findings. This work enriches the sensing methodologies based on PT-symmetric EPs, showing potential applications in implanted medical devices, industrial nondestructive testing, etc.