User:Audrey Buck/Quantum biology

Edits to Quantum Photosynthesis Section

- We will change instances of "antennas" to "antennae", as the latter refers to biology.

- We will remove the sentence "The claims of unexpected long coherence times sparked a lot of research in the quantum physics community to explain the origin.", as this sentence is redundant.

- The whole quantum photosynthesis section is difficult to read and includes grammatical errors. We will edit the original language for clarity.

-We will then add further information which we have researched, as follows:

Additions to the Photosynthesis Section

**Single molecule spectroscopy shows the quantum characteristics of photosynthesis without the interference of static disorder. (After the sentence starting with "However, critical follow-up...").

-Though Quantum Biology as a legitimate field of scientific inquiry found its beginnings in a 1943 book published by German physicist Pascual Jordan, it saw notable growth in tandem with the refinement of quantum information theory during the 1990s .

- The specific type of exciton generated in photosynthesis is the Frenkel exciton .

-(When discussing experiments that have demonstrated quantum coherence in photosynthetic mechanisms) -> A study published in 2007 identified electronic quantum coherence at −196 °C (77 K). Another, theoretical study from 2010 provided evidence that quantum coherence lives as long as 300 femtoseconds at biologically relevant temperatures (4 °C or 277 K) (same citation as in original article). In that same year, experiments conducted on photosynthetic cryptophyte algae using two-dimensional photon echo spectroscopy yielded further confirmation for long-term quantum coherence .

- (After last sentence in section)-> Indeed, research investigating transport dynamics suggests that interactions between electronic and vibrational modes of excitation in FMO complexes require a semi-classical, semi-quantum explanation for the transport of exciton energy. In other words, while quantum coherence dominates in the short-term, a classical description is most accurate to describe long-term behavior of the excitons

- (For second paragraph) Instead, as early as 1938, quantum coherence was theorized to be the mechanism for excitation energy transfer. Only recently, however, have scientists been able to experimentally explore this idea .

- (at end of section) Another process in photosynthesis that has almost 100% efficiency is charge transfer, again suggesting that quantum mechanical phenomena are at play . In 1966, a study on the photosynthetic bacteria Chromatium found that at temperatures below 100 K, cytochrome oxidation is temperature-independent, slow (on the order of milliseconds), and very low in activation energy. The authors, Don DeVault and Britton Chase, postulated that these characteristics of electron transfer are indicative of quantum tunneling, whereby electrons penetrate a potential barrier despite possessing less energy than is classically necessary .

Maybe we can add a little more info about charge transfer?

IMPLEMENTING ADDITIONS

Organisms that undergo photosynthesis absorb light energy through the process of electron excitation in antennae. These antennae vary among organisms. Bacteria use ring-like antennae, whereas plants and other organisms use chlorophyll pigments to absorb photons. Photosynthesis creates Frenkel excitons, which create a separation of charge that cells can convert into useable chemical energy. The energy collected in reaction sites must be transferred quickly before it is lost to fluorescence or thermal vibrational motion.

Various structures are responsible for transferring energy from antennae to a reaction site. One of the most well-studied is the FMO complex in green sulfur bacteria. FT electron spectroscopy studies show an efficiency of above 99% between the absorption of electrons and transfer to the reaction site with short lived intermediates. This high efficiency cannot be explained by classical mechanical models like the diffusion model. Instead, as early as 1938, quantum coherence was theorized to be the mechanism for excitation energy transfer.

Scientists have recently looked for experimental evidence of this proposed energy transfer mechanism. A study published in 2007 identified electronic quantum coherence at −196 °C (77 K). Another, theoretical study from 2010 provided evidence that quantum coherence lives as long as 300 femtoseconds at biologically relevant temperatures (4 °C or 277 K) (same citation as in original article). In that same year, experiments conducted on photosynthetic cryptophyte algae using two-dimensional photon echo spectroscopy yielded further confirmation for long-term quantum coherence. These studies suggest that, through evolution, nature has developed a way of protecting quantum coherence to enhance the efficiency of photosynthesis. However, critical follow-up studies question the interpretation of these results. Single molecule spectroscopy now shows the quantum characteristics of photosynthesis without the interference of static disorder, and some studies use this method to assign the signatures of electronic quantum coherence to the nuclear dynamics occurring in the chromophores. A number of proposals emerged trying to explain the unexpectedly long coherence times. According to one proposal, if each site within the complex feels its own environmental noise, the electron will not remain at any local minimum due to both quantum coherence and thermal environment, but proceed to the reaction site via quantum walks. Another proposal is that the rate of quantum coherence and electron tunneling create an energy sink that moves the electron to the reaction site quickly. Other work suggests that geometric symmetries in the complex may favor efficient energy transfer to the reaction center, mirroring perfect state transfer in quantum networks. Furthermore, experiments with artificial dye molecules cast doubts on the interpretation that quantum effects last any longer than one hundred femtoseconds.

In 2017, the first control experiment with the original FMO protein under ambient conditions confirmed that electronic quantum effects are washed out within 60 femtoseconds, while the overall exciton transfer takes a few picoseconds. In 2020 a review based on a wide collection of control experiments and theory concluded that the original claim of quantum effects as long lived electronic coherences in the FMO system does not hold. Instead, research investigating transport dynamics suggests that interactions between electronic and vibrational modes of excitation in FMO complexes require a semi-classical, semi-quantum explanation for the transport of exciton energy. In other words, while quantum coherence dominates in the short-term, a classical description is most accurate to describe long-term behavior of the excitons.

Another process in photosynthesis that has almost 100% efficiency is charge transfer, again suggesting that quantum mechanical phenomena are at play . In 1966, a study on the photosynthetic bacteria Chromatium found that at temperatures below 100 K, cytochrome oxidation is temperature-independent, slow (on the order of milliseconds), and very low in activation energy. The authors, Don DeVault and Britton Chase, postulated that these characteristics of electron transfer are indicative of quantum tunneling, whereby electrons penetrate a potential barrier despite possessing less energy than is classically necessary .