Thresholdless Coherent Light Scattering from Subband-polaritons in a Strongly-Coupled Microcavity

TL;DR

This paper demonstrates thresholdless coherent light scattering from subband-polaritons in a strongly-coupled microcavity, revealing sharp sideband peaks with high sensitivity and potential applications in optical communications.

Contribution

It introduces a novel strongly-coupled polariton system exhibiting thresholdless coherent scattering with ultra-sensitive detection capabilities.

Findings

Sharp sideband spectral peaks observed in backscattered light

Sideband intensity tracks polariton density precisely

Detection sensitivity exceeds quantum noise floor by over 2500 times

Abstract

We study a "strongly-coupled" (SC) polariton system formed between the atom-like intersubband transitions in a semiconductor nanostructure and the THz optical modes that are localised at the edges of a gold aperture. The polaritons can be excited optically, by incoherent excitation with bandgap radiation, and we find that they also coherently scatter the same input laser, to give strikingly sharp "sideband" (SB) spectral peaks in the backscattered spectrum. The SB intensity is a sensitive track of the polariton density and they can be detected down to a quantum noise floor that is more than 2500 times lower than the excitation thresholds of comparable quantum cascade laser diodes. Compared with other coherent scattering mechanisms, higher order SB scattering events are readily observable, and we speculate that the effect may find utility as a passive all-optical wavelength shifting mechanism in telecommunications systems.