Noise-resilient exceptional point sensing with immunity to undesired perturbations.

Abstract

Exceptional point degeneracies (EPDs) are non-Hermitian singularities where <i>K</i> eigenvalues and their corresponding eigenvectors coalesce. When a small perturbation is induced, the eigenvalue detuning from an EPD follows a <i>K</i>th-root sublinear expansion, which provides a means of enhancing the sensitivity (frequency shift) of resonant-based sensors. On the downside, resonant-based sensors are susceptible to cavity imperfections, local mechanical disturbances (temperature variations, vibrations), and other experimental uncertainties. Here, we overcome this problem by experimentally implementing passive periodic microwave metamaterials with nonresonant EPDs (NR-EPDs) occurring in their Bloch spectrum. We demonstrate a sublinear variation of the reflectance near NR-EPDs to a specific class of (global) perturbations and propose its usage for ultrasensitive sensing that is immune to undesired (local) perturbations. The sensitivity is shielded from technical or fundamental noise that typically degrades the signal-to-noise performance of resonant EPDs.