How Markovian is exciton dynamics in purple bacteria?

Area of Science:

• Quantum Biology
• Spectroscopy
• Biophysics

Background:

• Light-harvesting complex II (LH2) in purple bacteria plays a crucial role in photosynthesis.
• Understanding exciton dynamics is key to comprehending energy transfer efficiency.

Purpose of the Study:

• To assess the validity of the Markovian approximation for exciton dynamics in LH2.
• To quantify non-Markovian effects using novel measures.

Main Methods:

• Developed and applied measures based on Lindblad dynamics fitting and trace-distance.
• Utilized the hierarchical equation-of-motion method to model exciton-chromophore interactions.
• Incorporated broad, low-frequency, and underdamped high-frequency phonon bath modes.

Main Results:

• A smooth phonon bath shows minor non-Markovianity, but Lindblad dynamics require modification.
• High-frequency vibrational modes cause significant deviations from Markovian evolution.
• Resonant modes with excitonic spectrum gaps most strongly deviate from the Lindblad approximation.

Conclusions:

• The Markovian approximation is insufficient for describing exciton dynamics in LH2 under certain conditions.
• The spectral density's high-frequency structure critically influences exciton dynamics.
• Non-Markovian effects are substantial and depend on specific vibrational modes.