Non-hermitian exciton dynamics in a photosynthetic unit system

TL;DR

This paper explores non-hermitian quantum dynamics of excitonic energy transfer in photosynthetic systems, revealing the interplay of coherence and incoherence, exceptional points, and dissipation effects using a Green's function approach.

Contribution

It introduces a Green's function formalism to analyze non-hermitian exciton dynamics, highlighting the role of dissipation and exceptional points in photosynthetic energy transfer.

Findings

Identification of coherent-incoherent crossover at critical temperatures.

Observation of exceptional points at the transition regime.

Analysis of wavepacket evolution and quantum brachistochrone times in photosynthetic dimers.

Abstract

The non-hermitian quantum dynamics of excitonic energy transfer in photosynthetic systems is investigated using a dissipative two-level dimer model. The approach is based on the Green's function formalism which permits consideration of decoherence and intersite transfer processes on comparable terms. The results indicate a combination of coherent and incoherent behavior at higher temperatures with the possibility of exceptional points occurring at the coherent-incoherent crossover regime at critical temperatures. When each dimer site is coupled equally to the environmental sources of dissipation, the excitonic wavepacket evolves with time with a coherent component, which can be attributed to the indistinguishability of the sources of dissipation. The time evolution characteristics of the B850 Bchls dimer system is analysed using typical parameter estimates in photosynthetic systems, and the quantum brachistochrone passage times are obtained for a range of parameters.