Exceptional-Point-Enhanced Superior Sensing Using Asymmetric Coupled-Lossy-Resonator Based Optical Metasurface

Exotic optical responses of designed metasurfaces, including non-Hermitian photonic systems exhibiting exceptional point (EP)-singularities, offer diverse applications in the field of quantum sensing, laser technology, gravitational-wave detection as well as biomedical instrumentation for weak signal detection. However, the sensitivity enhancement of such EP-sensors is limited by quantum/thermal noises. Here we propose a novel scheme of EP-based superior photonic sensing of any molecule, using suitably designed asymmetric coupled-lossy-resonators (ACLR) with a non-Hermitian Hamiltonian. Unlike conventional approach of EP-degeneracy lifting, the perturbing Hamiltonian of the molecular-vibron, in the present method, generates an EP-singularity by coupling with the ACLR that does not exhibit EP in the unperturbed condition. Raman spectroscopic measurements performed on such systems provide significantly enhanced peaks at the vibronic modes, thereby exploring a novel method for molecule detection with superior sensitivity. Such EP-sensing is experimentally demonstrated in the current work by detecting the relevant protein-vibrons of the recombinant Omicron strain of SARS-CoV-2 with 350%-2200% enhanced Raman intensities, using an optical-metasurface consisting of an array of Au-asymmetric split-ring-resonators as the ACLRs. This work will open up a novel field of EP-based superior photonic sensing of any molecule, in general, by appropriately designing the ACLR-structures for detecting molecular-vibrons with desired enhanced sensitivity.