Strong coupling between chlorosomes of photosynthetic bacteria and a confined optical cavity mode.

David M Coles,Jason M Smith,Joseph Kuo-Hsiang Tang,David G Lidzey,Yaya Wang,Robert A Taylor,Semion K Saikin,Alán Aspuru-Guzik,Yanshen Yang,Richard T Grant

doi:10.1038/ncomms6561

Abstract

Strong exciton-photon coupling is the result of a reversible exchange of energy between an excited state and a confined optical field. This results in the formation of polariton states that have energies different from the exciton and photon. We demonstrate strong exciton-photon coupling between light-harvesting complexes and a confined optical mode within a metallic optical microcavity. The energetic anti-crossing between the exciton and photon dispersions characteristic of strong coupling is observed in reflectivity and transmission with a Rabi splitting energy on the order of 150 meV, which corresponds to about 1,000 chlorosomes coherently coupled to the cavity mode. We believe that the strong coupling regime presents an opportunity to modify the energy transfer pathways within photosynthetic organisms without modification of the molecular structure.

Highlights

Strong exciton–photon coupling is the result of a reversible exchange of energy between an excited state and a confined optical field
It is generally assumed that the light-harvesting complex (LHC) of these bacteria has evolved to efficiently collect and use the small amount of light available
We show that the energy of polariton modes can be detuned from the bare exciton states on the order of 100 meV, which is comparable to the energy difference between the chlorosome and the baseplate. We suggest that such structures could be used for the strong coupling of living photosynthetic bacteria with light to create ‘living polaritons’

Summary

Introduction

Strong exciton–photon coupling is the result of a reversible exchange of energy between an excited state and a confined optical field This results in the formation of polariton states that have energies different from the exciton and photon. The energetic anti-crossing between the exciton and photon dispersions characteristic of strong coupling is observed in reflectivity and transmission with a Rabi splitting energy on the order of 150 meV, which corresponds to about 1,000 chlorosomes coherently coupled to the cavity mode. Strong and coherent interaction between the pigment molecules in LHCs results in the formation of delocalized exciton states with the energies sufficiently different from non-interacting pigments[16,17] Such excitons are transferred across these collective as well as single-pigment states. The requirements of strong coupling include a large absorption oscillator strength and narrow absorption line width for the exciton, and small cavity losses into leaky modes

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Results

Conclusion