Hidden optical nonlinearities in linear spectra of quantum emitter arrays

TL;DR

This paper reveals that emitter-emitter interactions in quantum arrays can induce nonlinear optical features in their linear spectra, challenging classical assumptions and enabling new spectral control mechanisms.

Contribution

It demonstrates that nonlinearities of individual emitters can manifest in the linear response of arrays without cavities, expanding understanding of light-matter interactions.

Findings

Linear spectra of coupled heterodimers and chains show vibrational sidebands.

Tuning anharmonicities controls spectral features systematically.

Nonlinearities emerge in linear spectra without cavities or symmetry constraints.

Abstract

Classical optical frameworks such as the discrete dipole approximation (DDA) assume that the linear spectrum of coupled quantum emitters can be computed solely from the linear susceptibilities of individual constituents. However, recent polariton studies show that cavity linear response can encode nonlinear optical susceptibilities. Here, we demonstrate that this phenomenon is more general: emitter-emitter interactions allow nonlinearities of individual emitters to emerge in the linear response of arrays, without cavities or permutational symmetry. To illustrate this phenomenon, we show linear spectra for coupled heterodimers and linear chains, and demonstrate that Raman features of individual monomers show up as vibrational sidebands of collective resonances. Moreover, tuning Raman-type anharmonicities enables systematic control of spectral features, establishing a genuine quantum optical effect in molecular aggregates and quantum emitter arrays, which goes beyond mean-field descriptions in light-matter interactions.