Signatures of coherent energy transfer and exciton delocalization in time-resolved optical cross correlations

TL;DR

This paper demonstrates how optical second-order cross correlations can reveal quantum features such as exciton delocalization, coherent energy transfer, and electronic coherence in a donor-acceptor light-harvesting system.

Contribution

It provides a theoretical framework linking time-resolved optical cross correlations to quantum properties of coupled emitters, highlighting their potential as signatures of quantum behavior.

Findings

Oscillation frequency quantifies energy transfer timescales.

Cross correlations reveal exciton delocalization degree.

Steady-state electronic coherence is directly observed.

Abstract

We investigate how optical second-order cross correlations witness the quantum features of a prototype donor-acceptor light-harvesting unit. By considering a pair of detuned two-level emitters electronically coupled and incoherently driven to a non-equilibrium steady-state, we gain insight into how electronic quantum properties such as exciton eigenstate delocalization, coherent energy transfer and steady-state electronic coherence, are manifested in the joint probability of emission or optical second-order cross correlation. Specifically, we show that the frequency associated with oscillations present in time-resolved second-order cross correlation functions quantifies not only the time scale of coherent energy transfer but also the degree of delocalization of the exciton eigenstates. Furthermore, we show that time-resolved cross correlations directly witness steady-state electronic coherence. Our work strengthens the idea that measurements of the intensity quantum cross correlations can provide distinctive signatures of the quantum behavior of biophysical emitters.