Evanescent quadrupole polariton

TL;DR

This paper reports the creation of a new evanescent quadrupole polariton at an interface, with potential applications in Bose-Einstein condensation due to its long lifetime and coherent properties.

Contribution

It introduces a novel type of polariton formed via evanescent coupling between whispering gallery modes and quadrupole excitons in cuprous oxide.

Findings

Evanescent quadrupole polaritons have a lifetime of 1.7 ns.

The lower polariton branch shows a well-defined minimum.

Spatial coherence can be enhanced by arranging micro-spheres in a chain.

Abstract

In the work we demonstrate the formation of new type of polariton on the interface between a cuprous oxide slab and a polystyrene micro-sphere placed on the slab. The evanescent field of the resonant whispering gallery mode (WGM) has a substantial gradient, and therefore effectively couples with the quadrupole $1S$ excitons in cuprous oxide. This evanescent polariton has a long life-time ($1.7 ns$), which is determined only by its excitonic component. The polariton lower branch has a well pronounced minimum. This suggests that this excitation can be utilized for BEC. The spatial coherence of the polariton can be improved by assembling the micro-spheres in a linear chain.