Quantum biology

Journal name:
Nature Physics
Volume:
9,
Pages:
10–18
Year published:
DOI:
doi:10.1038/nphys2474
Received
Accepted
Published online

Abstract

Recent evidence suggests that a variety of organisms may harness some of the unique features of quantum mechanics to gain a biological advantage. These features go beyond trivial quantum effects and may include harnessing quantum coherence on physiologically important timescales. In this brief review we summarize the latest results for non-trivial quantum effects in photosynthetic light harvesting, avian magnetoreception and several other candidates for functional quantum biology. We present both the evidence for and arguments against there being a functional role for quantum coherence in these systems.

At a glance

Figures

  1. A quantum machine for efficient light-energy harvesting.
    Figure 1: A quantum machine for efficient light-energy harvesting.

    The well-studied FMO complex in the light-harvesting apparatus of green-sulphur bacteria exhibits some signatures of quantum coherent energy transfer. Experimental and theoretical works have scrutinized the precise mechanisms and quantumness of the energy transduction through this protein. Research in this field might reveal new quantum mechanical principles for improving the efficiency of energy harvesting in biology. a, Diagram of the photosynthetic apparatus of green sulphur bacteria, including its antenna, energy-conducting baseplate and FMO complexes, and reaction centre. The chlorosome antenna (green discs) is composed of roughly 200,000 BChl-c molecules, and is an exceptionally large structure that is designed to capture as many photons as possible in the low-light conditions the bacteria thrive in. Sunlight creates an excitation in this antenna that is transferred (red arrows) to the reaction centre through one of several FMO complexes. b, The BChl-a arrangements of one of the FMO pigment-protein complexes through X-ray diffraction. The FMO complex comprises eight (although only seven are shown here) bacteriochlorophyll-a (BChl-a) molecules that are encased in a protein scaffolding (not shown). The excitation arrives from the chlorosome at one of the sites, typically thought to be the site denoted as 1. This excitation is then transported from one BChl molecule to the next. Once it arrives at site 3 it can irreversibly enter the reaction centre and start a charge-separation process.

  2. The avian quantum compass.
    Figure 2: The avian quantum compass.

    The radical-pair mechanism for avian magnetoreception explains many of the behavioural studies performed on some species of migrating birds. Key properties of the proposed radical-pair model for avian magnetoreception are dependent on quantum mechanics; therefore, this may represent a functional piece of biological quantum hardware. a, A schematic of the radical-pair mechanism for magnetoreception that could potentially be employed by European robins and other species. It is thought to occur within cryptochromes, proteins residing in the retina. There are three main steps in this mechanism. First, light-induced electron transfer from one radical-pair-forming molecule (for example, in a cryptochrome in the retina of a bird) to an acceptor molecule creates a radical pair. b,c, Second, the singlet (S) and triplet (T) electron-spin states inter-convert owing to the external (Zeeman) and internal (hyperfine) magnetic couplings. d, Third, singlet and triplet radical pairs recombine into singlet and triplet products, respectively, which are biologically detectable. e, Singlet yield (a measure of the probability of the radical pair to decay into a singlet state) as a function of the external-field angle θ in the presence of an oscillatory field (taken from Gauger et al. 70). The blue top curve shows the yield for a static geomagnetic field (B0=47μT), and the red curves show the singlet yield in the case where a 150nT field oscillating at 1.316MHz is superimposed perpendicular to the direction of the static field. The sensitivity of the compass can be understood as the difference in the yield between θ=0 and θ=π/2. An appreciable effect on this sensitivity occurs once κ (the decay rate of the radical) is of order 104s−1. f, Singlet yield as a function of the magnetic field angle θ for differing noise magnitudes (from Gauger et al. 70). The blue curve shows the optimal case with no noise (but with decay rate κ=104s−1). The red curves indicate that a general noise rate of Γ>0.1κ has a detrimental effect on the sensitivity. Both of these results indicate that the electron spin state must have a remarkably long coherence time.

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Affiliations

  1. Advanced Science Institute, RIKEN, Saitama 351-0198, Japan

    • Neill Lambert &
    • Franco Nori
  2. Department of Physics and National Center for Theoretical Sciences, National Cheng Kung University, Tainan 701, Taiwan

    • Yueh-Nan Chen &
    • Guang-Yin Chen
  3. Department of Chemistry and Center for Quantum Science and Engineering, National Taiwan University, Taipei 106, Taiwan

    • Yuan-Chung Cheng
  4. Department of Engineering Science and Supercomputing Research Center, National Cheng Kung University, Tainan 701, Taiwan

    • Che-Ming Li
  5. Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1040, USA

    • Franco Nori

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