Quantitative investigations of quantum coherence for a light-harvesting protein at conditions simulating photosynthesis

Abstract

Recent measurements using two-dimensional electronic spectroscopy (2D ES) have shown that the initial dynamic response of photosynthetic proteins can involve quantum coherence. We show how electronic coherence can be differentiated from vibrational coherence in 2D ES. On that basis we conclude that both electronic and vibrational coherences are observed in the phycobiliprotein light-harvesting complex PC645 from Chroomonas sp. CCMP270 at ambient temperature. These light-harvesting antenna proteins of the cryptophyte algae are suspended in the lumen, where the pH drops significantly under sustained illumination by sunlight. Here we measured 2D ES of PC645 at increasing levels of acidity to determine if the change in pH affects the quantum coherence; quantitative analysis reveals that the dynamics are insensitive to the pH change.

The feasibility of coherent energy transfer in microtubules

“…Thus, we conclude that, based on this initial analysis, the unique Trp network within an individual tubulin dimer can possess significant dipolar couplings capable of supporting quantum coherent beating effects similar to those observed in the FMO photosynthetic complex [4,5], LHCII [7,8], LH2 [9,10] and phycobiliprotein LHCs [11,12]. Furthermore, our results suggest that this network may support coherent energy transfer at physiological temperature between clusters of Trps in tubulin, and microtubule structures.…”

“…This limit was further pushed to 277 K, nearing physiological temperature, and effectively ruling out the 'warm and wet' limit for quantum phenomena in biology [5]. Furthermore, these coherent effects do not seem to be restricted to the FMO complex alone, and have been shown for LHCs in plants (LHCII) [6][7][8], bacteria (LH2) [9,10] and phycobiliproteins [11,12].…”

Laser-Limited Signatures of Quantum Coherence

“…The importance of such a comparative study of measured results and the expected response based on calculations becomes immediately evident: even in a strongly coupled system where 2D spectral features are well-resolved, a multitude of dynamic contributions overlap in a nontrivial way. In particular, oscillatory signals associated with ground state vibrational wavepackets are strongly present at excitonic crosspeak locations, as was already emphasized by earlier studies [16,[23][24][25][26]. Using numerical predictions, we nevertheless managed to accurately extract the coherence between the two most radiant states of the homodimer system through excited state absorption features.…”

“…However, even for such simple molecules, vibronic coupling automatically gives rise to additional oscillating coherences of ground state vibrational wavepackets that might overlap with excited state features [16,23,24]. Studies aimed at disentangling vibrational and excitonic coherences in such cases have focused on limiting examples of purely vibrational and electronic excitations, and have not led to a consensus method for their distinction in measurements, without loss of generality [25,26].…”

Room-temperature exciton coherence and dephasing in two-dimensional nanostructures

“…This inhomogenous broadening results in an apparent shortening of the observed ensemble coherences called 'fake decoherence' 6,7 . Moreover, the presence of numerous vibrational modes in molecular chromophores 8 and even the (nonresonant) solvent 9 makes interpretation of the coherent signals in time-resolved experiments particularly challenging. To try to circumvent these complexities, analyses of oscillation amplitudes in 2D maps have been developed 10 .…”