When is Biology Quantum?

The absorption of quanta of light (photons) is important for many biological processes such as vision, photosynthesis, and animal magnetoreception (birds, for instance, navigate by sensing how the Earth’s magnetic field steers electrons photogenerated in their retinas). Typically, photons are absorbed by some pigment-protein complex, triggering a sequence of chemical reactions that realize a biological function. Researchers have suggested that quantum effects play a role in these processes, but a quantitative assessment of their impact has proved problematic. Now, Atac Imamoglu at the Swiss Federal Institute of Technology (ETH) in Zurich and Birgitta Whaley at the University of California, Berkeley, have described these reactions as quantum measurements, in which the pigment-protein complex acts as a quantum meter measuring the incident light. They propose a new Hamiltonian model that can assess whether quantum coherence is an essential requirement for a given process.