The future of quantum biology

Abstract

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, and here we provide an outline of the current state of the field, as well as insights into future directions.

Keywords: artificial photosynthesis; charge transfer; enzyme catalysis; light harvesting; quantum technology; sensing.

Figure 1.

A schematic illustrating the concept of excitation energy transfer in photosynthetic light-harvesting complexes. The ovals depict pigment clusters in which strong excitonic coupling occurs while the arrows represent incoherent transfer of the energy amongst the clusters. Within each cluster, the energy is delocalized over all pigments and is transferred coherently.

Figure 2.

Schematic of quantum-coherent charge separation in the Photosystem II reaction centre of higher plants along one of at least two existing pathways, according to the model in [23]. On the left are four wavepackets on harmonic potentials, each corresponding to a different state along the charge separation pathway. For each state, the key pigments and approximate location and sign of the charge clouds are shown on the right. Horizontal lines depict absorption peaks at the specified wavelength of the corresponding state shown on the right, while the wavy arrows depict resonance interaction with the indicated vibrational mode. The symbols δ and * represent charge-transfer character and exciton character, respectively. The nature of the four states are —a high exciton state, —an exciton state with some charge-transfer character, —a charge-transfer state mixed with an exciton state, and —the final charge-separated state. Note that an intermediate between the last two states, involving Chl_D1, is omitted. The first three steps involve coherent relaxation due to coupling with a vibrational mode, while the last step involves incoherent transfer. Symbols: D1 and D2, two branches of the symmetric reaction centre structure; Chl, chlorophyll; P, primary electron donor/special-pair Chl; Phe, pheophytin. Adapted from Romero et al. [23].

Figure 3.

The three steps of the radical pair mechanism. In the first step, a photon incident on the donor molecule causes one of the electrons of the pair to be donated to the acceptor to create the spatially separated but spin-correlated radical pair. In the second step, the radical pair oscillates between singlet and triplet states under the influence of the Zeeman and hyperfine effects. The third step is comprised of spin-dependent recombination into the chemical product.

Figure 4.

A schematic illustrating the possible role of quantum effects in olfaction. Where previously olfaction has been proposed to depend on the shape and size of odourants fitting a specific receptor, experiments with fruit flies have indicated that the substitution of hydrogen with deuterium results in an odour change in spite of their having the same shape. This suggests that vibrational frequency might play a role in the detection of odourants [111].