Phys. Rev. E 91, 022714 (2015)

The absorption of light is responsible for triggering many biological sensing and regulation processes, including vision, photosynthesis and magnetoreception — the ability of some living organisms to detect the magnitude and orientation of the Earth's magnetic field, thought to be important for migration. These phenomena share common features, such as the excitation of a photosensitive molecule within a pigment–protein complex, which in turn sets off a series of chemical reactions leading to biological functionality. However, the fundamental mechanisms at play are unclear.

Now, a theoretical framework for understanding photoactivated biological processes as quantum measurements has been proposed. Borrowing ideas from magnetometry techniques, in which electron spins can act as quantum meters to sense weak magnetic fields, Atac Imamoglu and K. Birgitta Whaley have suggested that the pigment–protein complexes may act as quantum meters of incident radiation. In doing so, they have established when quantum coherence is essential for ensuring the biological functionality of a given photoactivated process, and when it is not. The authors identified magnetoreception as one example in which quantum coherent dynamics are crucial, providing experimentalists with a testable hypothesis for a largely confounding effect.