When is biology quantum?

Black-winged stilts and northern pintails in Visakhapatnam in February 2014. Animal magnetoreception, an example of which is navigation by birds, is a biological process for which quantum effects are essential.

BIOLOGICAL processes such as vision, photosynthesis and animal magnetoreception (for example, navigation by birds by sensing how much the earth’s magnetic field steers electrons created by impinging photons in their retinas) require the absorption of quanta of light (photons). This is a quantum mechanical process. In biological processes, it would typically be a pigment-protein complex that would absorb the photons. This in turn would initiate a string of chemical reactions leading to a biological function. But it has been difficult to quantify the degree of impact of this “quantumness”, say, for instance, in the efficiency or the outcome of the biological process.

Researchers at the Swiss Federal Institute of Technology Zurich and the University of California, Berkeley, have come up with a model that can measure how quantum dynamics affects photo-induced biological functions. The model treats these reactions as quantum measurements where the pigment-protein complex acts as a quantum meter measuring the incident light. Photon absorption generates bunches of excited electrons with correlations between them (coherence).

According to the model, the extent of quantumness is determined by the measure of quantum coherence in the excited electrons that is retained in the chain of chemical reactions that follow. Applying their formalism to different photon-induced biological processes, the authors concluded that magnetoreception is the only one for which quantum effects are truly essential.

This work was published in a recent issue of Physical Review E.