Reconfigurable exceptional point-based sensing with 0.001λ sensitivity using spoof localized surface plasmons

Recent breakthroughs in the field of non-Hermitian physics present unprecedented opportunities, from fundamental theories to cutting-edge applications such as multimode lasers, unconventional wave transport, and high-performance sensors. The exceptional point, a spectral singularity widely existing in non-Hermitian systems, provides an indispensable route to enhance the sensitivity of optical detection. However, the exceptional point of the forementioned systems is set once the system is built or fabricated, and machining errors make it hard to reach such a state precisely. To this end, we develop a highly tunable and reconfigurable exceptional point system, i.e., a single spoof plasmonic resonator suspended above a substrate and coupled with two freestanding Rayleigh scatterers. Our design offers great flexibility to control exceptional point states, enabling us to dynamically reconfigure the exceptional point formed by various multipolar modes across a broadband frequency range. Specifically, we experimentally implement five distinct exceptional points by precisely manipulating the positions of two movable Rayleigh scatterers. In addition, the enhanced perturbation strength offers remarkable sensitivity enhancement for detecting deep-subwavelength particles with the minimum dimension down to 0.001λ (with λ to be the free-space wavelength).