Quantum Biology

Quantum biology is concerned with the influence of non-trivial quantum phenomena, which can be explained by reducing the biological process to fundamental physics, although these effects are difficult to study and can be speculative.

Such processes involve chemical reactions, light absorption, formation of excited electronic states, transfer of excitation energy, and the transfer of electrons and protons (hydrogen ions) in chemical processes, such as photosynthesis, olfaction and cellular respiration.

Photosynthesis is a highly optimized process from which valuable lessons can be learned about the operating principles in nature. Its primary steps involve energy transport operating near theoretical quantum limits in efficiency. Recently, extensive research was motivated by the hypothesis that nature used quantum coherences to direct energy transfer.

This body of work, a cornerstone for the field of quantum biology, rests on the interpretation of small-amplitude oscillations in two-dimensional electronic spectra of photosynthetic complexes. Some Review discusses recent work reexamining these claims and demonstrates that interexciton coherences are too short lived to have any functional significance in photosynthetic energy transfer. Instead, the observed long-lived coherences originate from impulsively excited vibrations, generally observed in femtosecond spectroscopy. These efforts, collectively, lead to a more detailed understanding of the quantum aspects of dissipation.

Nature, rather than trying to avoid dissipation, exploits it via engineering of exciton-bath interaction to create efficient energy flow.

Biological systems are dynamical, constantly exchanging energy and matter with the environment in order to maintain the non-equilibrium state synonymous with living.

Developments in observational techniques have allowed us to study biological dynamics on increasingly small scales.

Such studies have revealed evidence of quantum mechanical effects, which cannot be accounted for by classical physics, in a range of biological processes.

Quantum biology is the study of such processes,

The first book on quantum biology is entitled Physics of the mystery of organic molecules by Pascual Jordan .

Since its publication in 1932, however, many mysteries about the nature of life remain.

It is clear that coarse-grained classical models fail to give an accurate picture of a range of processes taking place in living systems.

The matter of ongoing debate then, is the extent to which quantum effects play a non-trivial role in such biological processes.

A useful path towards answering this question is through the engineering of biologically inspired quantum technologies that can outperform classical devices designed for the same purpose, for example, for energy harnessing or environmental sensing.

If quantum effects on a macroscopic scale play a role in getting the job done better in certain processes perfected over billions of years at physiological temperatures and in immensely complex systems, then there exists a wealth of information in the biological world from which to draw inspiration for our own technologies.

In this direction, a prototype quantum heat engine, which clearly illustrates a quantum design principle whereby a coherent exchange of single energy quanta between electronic and vibrational degrees of freedom can enhance a light-harvesting system’s power above what is possible by thermal mechanisms alone, has been proposed.

Its quantum advantage using thermodynamic measures of performance has been quantified, and the principle’s applicability for realistic biological structures demonstrated .

Quantum biology investigates biological function and regulation of this function, which is connected to static disorder.

Single molecule spectroscopy gives us a unique, powerful lens on the role of static disorder, which connects biological function (i.e. projected onto the macroscopic/organismal scale) with quantum-mechanical phenomena.

Quantum biology is also concerned with interactions between dynamical phenomena at well-separated length and time scales, from femtosecond energy transfer processes in molecular assemblies at the nanoscale to survival and reproduction within ecosystems at the scales of overall organisms.

While quantum biology is set to demonstrate in the next few decades the extent to which bioinspired quantum devices can outperform classical analogues, a deeper question is how quantum-dynamical phenomena at the nanoscale can provide a selective advantage to an overall organism.

Addressing this question rigorously demands an account of how macroscale physical observables significant to organismal fitness can depend predictably on nanoscale quantum dynamical variables.

Reciprocally, we must also account for how quantum subsystems at the nanoscale can depend on macroscale dynamics of organisms through evolution.

Progress on this question may be assisted by a theoretical framework that allows organism-scale models to be parametrized by nanoscale models.

This may be provided by the tools of multiscale analysis within the field of complex systems theory.

We might also conceive of experiments in which wild-type organisms known to exhibit long-lived quantum-coherent processes at the nanoscale compete with genetically modified organisms in which such processes are known to be absent.

Such an experiment—akin to those done regularly by biologists—may offer clear insight into whether quantum-biological phenomena can provide a selective advantage to organisms, as well add credibility to quantum biology as a field of biology.

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