The evidence that evolution has harnessed quantum entanglement, the subject of another recent report, continues to build. Berkeley scientists have modeled the existence of quantum entanglement in a biological structure for the first time. They have shown that, during photosynthesis, these entangled states can exist at high, physiologically relevant temperatures and relatively long timescales.

Classically, one can describe a system by separately considering the energy, momentum, position, or “state” of each of the constituent parts that make up that system. In an entangled quantum system, the state of each part may be related to the state of other parts of the system—they are no longer independent. Quantum entanglement can occur even if the parts are physically separated.

Photosynthesis in green sulphur bacteria is accomplished by a light-harvesting apparatus in three basic steps. First, a chlorosome antenna captures photons. Second, the energy from the captured photon is transferred from the antenna through the Fenna-Matthews-Olson protein (FMO) to the reaction core. Finally, the energy is used by the reaction core to do chemical work.

The FMO is a trimer of proteins, each of which contains seven bacteriochlorophyll-a molecules. In their work, the scientists have shown that that the states of these bacteriochlorophyll-a molecules could be entangled to one another.

Their model has predicted entangled states in the FMO complex at high temperatures—about 300K, which is above room temperature—and shown that the entangled states exist at measurable time scales. The authors note that the FMO complex may be too small to take advantage of the entangled states, but theorize that entangled states in more complex photosynthesis systems may increase the efficiency, regularity, and robustness of photosynthesis. The entangled states can’t be detected at present, but the models have laid out what we should be looking for using new methods that are under development.

Nature Physics, 2010. DOI: 10.1038/nphys1652 (About DOIs).