Photon correlation spectroscopy as a witness for quantum coherence

TL;DR

This paper proposes photon correlation spectroscopy as a novel method to detect and analyze quantum coherence in driven-dissipative molecular systems, offering new insights into quantum dynamics in biological and chemical contexts.

Contribution

It introduces photon correlation measurements as a new spectroscopic tool capable of identifying quantum coherence in steady and transient states of molecular aggregates.

Findings

Photon correlation statistics can signal quantum coherence in steady states.

Deviations from independent emitter statistics indicate quantum coherence.

Frequency-resolved correlations reveal coherent dynamics without steady state coherence.

Abstract

The development of spectroscopic techniques able to detect and verify quantum coherence is a goal of increasing importance given the rapid progress of new quantum technologies, the advances in the field of quantum thermodynamics, and the emergence of new questions in chemistry and biology regarding the possible relevance of quantum coherence in biochemical processes. Ideally, these tools should be able to detect and verify the presence of quantum coherence in both the transient dynamics and the steady state of driven-dissipative systems, such as light-harvesting complexes driven by thermal photons in natural conditions. This requirement poses a challenge for standard laser spectroscopy methods. Here, we propose photon correlation measurements as a new tool to analyse quantum dynamics in molecular aggregates in driven-dissipative situations. We show that the photon correlation statistics on the light emitted by a molecular dimer model can signal the presence of coherent dynamics. Deviations from the counting statistics of independent emitters constitute a direct fingerprint of quantum coherence in the steady state. Furthermore, the analysis of frequency resolved photon correlations can signal the presence of coherent dynamics even in the absence of steady state coherence, providing direct spectroscopic access to the much sought-after site energies in molecular aggregates.