Single-photon absorption and emission from a natural photosynthetic complex

Area of Science:

• Biophysics
• Photosynthesis Research
• Quantum Biology

Background:

• Photosynthesis is traditionally assumed to be triggered by a single photon from the sun.
• Previous research has explored photosynthesis using intense laser pulses, not single photons under ambient conditions.
• The light-harvesting 2 (LH2) complex in Rhodobacter sphaeroides contains B800 and B850 bacteriochlorophyll rings.

Purpose of the Study:

• To investigate whether single photons can initiate the photosynthetic process in the LH2 complex under ambient conditions.
• To establish a time correlation between single-photon excitation and fluorescence emission.
• To confirm the role of single photons in driving subsequent energy transfer and charge separation.

Main Methods:

• Utilized a heralded single-photon source for excitation.
• Employed coincidence counting to establish time correlations.
• Analyzed fluorescence emission from the LH2 complex of Rhodobacter sphaeroides.
• Developed analytical stochastic and Monte Carlo numerical models.

Main Results:

• Demonstrated that both B800 excitation and B850 fluorescence emission involve single photons.
• Established a time correlation between single-photon excitation and fluorescence emission.
• Showed that the probability distribution supports single-photon-driven energy transfer and fluorescence.

Conclusions:

• Single photons can initiate photosynthesis by driving energy transfer and fluorescence emission in the LH2 complex.
• The findings confirm the role of single photons in the primary charge separation of photosynthesis.
• This study validates the use of single photons to probe natural light-harvesting complexes.