Excitonic Coupling and Photon Antibunching in Venus Yellow Fluorescent Protein Dimers: A Lindblad Master Equation Approach

TL;DR

This paper models Venus yellow fluorescent protein dimers using a Lindblad master equation to explain the coexistence of strong excitonic coupling and photon antibunching without long-lived quantum coherence.

Contribution

It provides a theoretical framework that reconciles excitonic coupling and photon antibunching in YFP dimers through simulations, highlighting the need for model adjustments.

Findings

Simulations predict femtosecond decoherence times.

Bright/dark state mixtures match antibunched fluorescence.

Standard Lindblad assumptions may require modification.

Abstract

Strong excitonic coupling and photon antibunching (AB) have been observed together in Venus yellow fluorescent protein dimers and currently lack a cohesive theoretical explanation. In 2019, Kim et al. demonstrated Davydov splitting in circular dichroism spectra, revealing strong J-like coupling, while antibunched fluorescence emission was confirmed by combined antibunching--fluorescence correlation spectroscopy (AB/FCS fingerprinting). To investigate the implications of this coexistence, Venus yellow fluorescent protein (YFP) dimer population dynamics are modeled within a Lindblad master equation framework, testing its ability to cope with typical, data-informed, Venus YFP dimer time and energy values. Simulations predict multiple-femtosecond (fs) decoherence, yielding bright/dark state mixtures consistent with antibunched fluorescence emission at room temperature. Thus, excitonic coupling and photon AB in Venus YFP dimers are reconciled without invoking long-lived quantum coherence. However, clear violations of several Lindblad approximation validity conditions appear imminent, calling for careful modifications to choices of standard system and bath definitions and parameter values.