Observed enhanced emission at higher-order exceptional points in RF circuits

TL;DR

This paper demonstrates that RF cavities engineered with higher-order exceptional points exhibit enhanced emission due to non-Lorentzian local density of states, offering a new approach to cavity design beyond traditional high-Q resonators.

Contribution

It introduces a novel cavity design leveraging higher-order exceptional points to achieve enhanced emission without requiring ultrahigh Q-factors.

Findings

Enhanced emissivity increases with the order of the exceptional point

Experimental validation of non-Lorentzian local density of states

Theoretical analysis links enhancement to an N-th power Lorentzian line shape

Abstract

The Purcell effect -- stemming directly from the celebrated Fermi's Golden Rule -- links the enhanced emissivity of an emitter to the local density of states (LDoS) of a surrounding cavity. Under typical circumstances the LDoS is assumed to have a Lorentzian lineshape. Here, we go beyond the traditional Purcell framework by designing RF cavities with non-Lorentzian LDoS caused by higher-order non-Hermitian exceptional point degeneracies (EPDs) where $N\geq 2$ eigenfrequencies and their associated eigenmodes coalesce. We experimentally demonstrate a non-conventional emissivity enhancement (as compared to the isolated resonance regime) that increases with the EPD order $N$. The theoretical analysis traces its origin to an $N$-th power Lorentzian LDoS line shape that dominates under judicious spatially designed cavity losses. Our results reveal a new route to design cavities that do not rely on ultrahigh $Q$-factor resonators or small modal volumes.