Category University of South Australia

Natural Light Harvesting Systems: Unraveling the quantum puzzles

A. Thilagam

In natural light harvesting systems, the sequential quantum events of photon absorption by specialized biological antenna complexes, charge separation, exciton formation and energy transfer to localized reaction centers culminates in the conversion of solar to chemical energy. A notable feature in these processes is the exceptionally high efficiencies (> 95 %) at which excitation is transferred from the illuminated protein complex site to the reaction centers. Such high exciton propagation rates within a system of interwoven biomolecular network structures, is yet to be replicated in artificial light harvesting complexes. A clue to unraveling the quantum puzzles of nature may lie in the observation of long lived coherences lasting several picoseconds in the electronic spectra of photosynthetic complexes, even in noisy environmental baths. A number of experimental and theoretical studies have been devoted to unlocking the links between quantum processes and information protocols, in the hope of finding answers to nature’s puzzling mode of energy propagation. This review presents developments in quantum theories, and links information-theoretic aspects with photosynthetic light-harvesting processes in biomolecular systems. There is examination of various attempts to pinpoint the processes that underpin coherence features arising from the light harvesting activities of biomolecular systems, with particular emphasis on the effects that factors such non-Markovianity, zeno mechanisms, teleportation, quantum predictability and the role of multipartite states have on the quantum dynamics of biomolecular systems. A discussion of how quantum thermodynamical principles and agent-based modeling and simulation approaches can improve our understanding of natural photosynthetic systems is included.

Quantum Physics (quant-ph); Biological Physics (; Chemical Physics (physics.chem-ph)

Non-hermitian dynamics of the photosynthetic exciton

A. Thilagam

The non-hermitian quantum dynamics of excitonic energy transfer in photosynthetic systems is investigated using a dissipative two-level dimer model which incorporates radiative terms. 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 occuring 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 estimates in photosynthetic systems.
Quantum Physics (quant-ph)