Quantum coherence in photosynthesis: towards single-molecule light-conversion devices

ended

Photosynthesis performed by plants, algae and photosynthetic bacteria is the biological process that transforms solar energy into chemical energy with high quantum efficiency. A complete understanding of the factors that modulate the efficiency of this process is a challenge centered at the nexus of fundamental physics and biology, and obtaining that knowledge could pave the way for the design of the next generation of cheap and highly-efficient light-conversion devices. The main aim of this project is to understand how quantum coherence modulates the efficiency of photosynthesis. Quantum coherence is likely to be involved in not only the first ultrafast stages of excitation energy transfer in the photosynthetic light harvesting antenna but also in the charge separation process in the photosynthetic reaction center by coupling to specific vibrational states of this pigment-protein complex (Romero et al, Nature Physics 10, 676-682, 2014) . Here we propose to use time-resolved coherent anti-Stokes Raman spectroscopy and two-dimensional photon echo spectroscopy to demonstrate the specific vibrational modes that sustain quantum coherence at the single molecule level. Time-resolved anti-Stokes Raman spectroscopy will provide an insight into the specific vibrations in the molecule that lead to sustained quantum coherence in the charge separation steps of photosynthesis. Results will be confirmed using two-dimensional photon echo spectroscopy and rationalized in a Redfield theory framework. To assess the role of energetic disorder, reaction centers will also be characterized using a combination of single-molecule techniques in order to correlate the quantum coherence arising at the single-molecule level with the efficiency of the whole ensemble. To achieve this, a new technique capable of quantifying quantum coherence at the nanoscale will be developed. This new technique and its applications will deeply impact quantum biology and other fields.