How Can the Green Sulfur Bacteria in the Depths of the Black Sea Use Quantum Computing for Light Harvesting?

Abstract

Long lasting coherence in photosynthetic pigment-protein complexes has been observed even at physiological temperatures (1; 2; 3). Experiments have demonstrated quantum coherent behaviour in the long-time operation of the D-Wave quantum computer as well (4; 5). Quantum coherence is the common feature between the two phenomena. However, the 'decoherence time' of a single flux qubit, the component of the D-Wave quantum computer, is reported to be on the order of nanoseconds, which is comparable to the time for a single operation and much shorter than the time required to carry out a computation on the order of seconds. An explanations for the factor of 10 8 discrepancy between the single flux qubit coherence time and the long-time quantum behaviour of an array of thousand flux qubits was suggested within a theory where the flux qubits are coupled to an environment of particles called gravonons of high density of states (6; 7). The coherent evolution is in high dimensional spacetime and can be understood as a solution of Schrödinger's time-dependent equation.Explanations for the quantum beats observed in 2D Fourier transform electronic spectroscopy of the Fenna-Matthews-Olson (FMO) protein complex in the green sulfur bacteria are presently sought in constructing transport theories based on quantum master equations where 'good' molecular vibrations ('coloured noise') in the chlorophyll and the surrounding protein scaffold knock the exciton oscillations back into coherence (8; 9). These 'good' vibrations are claimed to have developed in three billion years of natural selection. These theories, however, face the discomforting experimental observation that "attempts to scramble vibrational modes or to shift resonances with isotopic substitution miserably failed to affect the beating signals" (10). As a possible way out of this dilemma we adopted the formalism of the quantum computation to the quantum beats in the FMO protein complex.

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“…Once captured by this antenna, the absorbed excitation energy from the sunlight is transferred to a photosynthetic reaction center via the Fenna-Matthews-Olsen (FMO) complex -a pigment protein complex -which links the antenna and the reaction center [153] . The FMO protein complex is made up of seven chlorophyll molecules located in a protein cavity [154] . These chlorophyll molecules are able to transiently store the energy captured by the antenna as electronic excited states in order to channel it to the reaction center, which can be thought as a solar cell.…”

“…Since this landmark work, a large number of papers have been published on this topic, with experimental work even suggesting that the coherence found is non-negligible for up to 300 fs, even at room temperature [2] . For example the FMO protein-chlorophyll complex of green sulfur bacteria demonstrates coherence for times in excess of 1000 fs even at high temperature (277 K) in the 2D Fourier transform electronic spectroscopy [40,154] . The earliest measurement of quantum coherence in photosynthetic organisms was carried out at temperatures far below room temperature [12] .…”

“…The earliest measurement of quantum coherence in photosynthetic organisms was carried out at temperatures far below room temperature [12] . However, it has been demonstrated that quantum beating can be demonstrated at room temperature after exciting the photosynthetic complexes with a laser pulse [6,154,157,158,159,160] .…”