U.S. Department of Energy - Energy Efficiency and Renewable Energy

Clean Cities

Scientists Find Photosynthesis Depends on Quantum Entanglement

May 19, 2010

Researchers at DOE's Lawrence Berkeley National Laboratory (LBNL) have discovered that photosynthesis depends on a relatively obscure physical phenomenon called quantum entanglement. Photosynthesis is the highly efficient process that plants use to convert sunlight and carbon dioxide into sugars and other chemicals, and scientists hope to one day mimic the process of photosynthesis to produce fuels and chemicals directly from sunlight. The new LBNL research sheds light on the process, but also reveals new unexpected levels of complexity.

Pigments in green plants and certain bacteria are able to capture energy from sunlight, and pigment-protein complexes are then able to transfer the energy into reaction centers at lightning speeds with nearly 100% efficiency. The LBNL researchers have found that the solar photons caused electronic oscillations in the closely packed pigment-protein complex, inducing similar electronic oscillations in the reaction centers. The wavelike oscillations occur on the scale of femtoseconds—millionths of a billionth of a second—and take advantage of the unique physics of quantum mechanics, which governs the behavior of atoms, photons, and other subatomic particles. Essentially, the wavelike quality of the oscillations allows them to simultaneously sample all the potential energy transfer pathways in the photosynthetic system and choose the most efficient. This is the key to the fast and efficient energy transfer within the photosynthetic system.

What remained unclear to the LBNL researchers was how the wavelike oscillations are sustained in the pigment-protein complex. The answer to that puzzle turns out to be quantum entanglement, a phenomenon that typically occurs between two subatomic particles, such as electrons. Electrons are often created in pairs, with one electron having a spin "up" and the other having a spin "down." According to quantum mechanics, the spin of each electron is not fixed until it is measured, existing instead as a probability of either choice. This remains true even when the electrons are separated at a great distance, but once the spin of one electron is measured, the other electron instantaneously assumes the opposite spin, because the two are entangled at a quantum level. Einstein referred to this effect as "spooky action at a distance."

According to the LBNL researchers, such quantum entanglement is present across the entire light harvesting complex and sustains the wavelike oscillation, marking the first time the effect has been examined and quantified in a real biological system. The scientists were surprised to find entanglement persisting for relatively long times at room temperature and between molecules that were not strongly coupled to one another. The findings have implications not only for mimicking photosynthesis, but also for quantum-based computing. See the LBNL press release.