Noise-resilient exceptional point sensing with immunity to undesired perturbations

Exceptional point degeneracies (EPDs) are non-Hermitian singularities
where eigenvalues and their corresponding eigenvectors coalesce. When a
small perturbation is induced, the eigenvalue detuning from an EPD follows
a 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
non-resonant EPDs (NR-EPD) 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
ultra-sensitive sensing that is immune to undesired (local) perturbations.
Importantly, the sensitivity is shielded from technical or fundamental
noise that typically degrades the signal-to-noise performance of resonant
EPDs.