Introduction to Quantum Coherence in Photosynthesis

Photosynthesis is a complex process by which plants and other photosynthetic organisms convert light energy into chemical energy. The process is efficient because it harnesses the energy of photons to drive the transfer of electrons through a series of molecular complexes. Scientists have long puzzled over how photosynthesis achieves such high efficiency, given that classical physics cannot fully explain the transfer of energy from one molecule to another. Quantum coherence has emerged as a possible explanation for the efficiency of photosynthesis.

How Photosynthesis Utilizes Quantum Coherence

Quantum coherence refers to the phenomenon where particles, such as electrons, can exist in multiple states simultaneously. In photosynthesis, this means that electrons can occupy two or more energy states simultaneously, allowing them to sample a larger range of energies and find the most efficient path through the molecular complexes. By doing so, the electrons can avoid wasting energy and ensure that the majority of the energy from photons is used in photosynthesis.

Evidence Supporting the Role of Quantum Coherence

Experiments have shown that photosynthetic organisms can maintain quantum coherence over long distances and in the presence of noise. For example, studies have shown that quantum coherence can persist in chlorophyll molecules for up to a few hundred femtoseconds, long enough for the molecules to transport energy to the reaction center. Additionally, theoretical models have predicted that quantum coherence can lead to a 30% improvement in the efficiency of photosynthesis.

Example of Quantum Coherence in Photosynthesis: the FMO Complex

One of the best-studied examples of quantum coherence in photosynthesis is the Fenna-Matthews-Olson (FMO) complex, which is found in green sulfur bacteria. The FMO complex acts as a bridge between the light-harvesting complexes and the reaction center, where the energy is converted into chemical energy. The complex consists of seven bacteriochlorophyll molecules, which are arranged in a ring-like structure. The arrangement of the molecules allows them to act as a quantum antenna, efficiently capturing and transporting energy to the reaction center. Experiments have shown that quantum coherence plays a crucial role in the energy transfer process in the FMO complex.