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 explanation 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.