Scientists Simulate Key Processes of Photosynthesis on a Quantum Level

Scientists have managed to simulate the key processes of photosynthesis on a quantum level with high spatial and temporal resolution. The findings are an important step toward answering the question of how quantum physics can contribute to the efficiency of energy conversion in synthetic systems.

The scientists first began with the question of how the energy of light can be efficiently collected and converted elsewhere into a different form--for example, into chemical or electrical energy. Nature has found a very efficient way to accomplish this in photosynthesis. Light energy is absorbed in an array of membrane proteins and then transported to a molecular reaction center through structures called nanoantennae. The light is then transformed into chemical energy. Duplicating this process artificial, though, is the hard part.

To tackle photosynthesis, the researchers used a gas of atoms that was cooled down to a temperature of near absolute zero. Some of the atoms were excited with laser light to high electric states. The excited electron of these "atomic giants" is separated by macroscopic distances of almost a hair's breadth from the atomic nucleus. This means that these atoms are ideal systems to study phenomena at the transition between the macroscopic and the microscopic. Similar to the light-harvesting complexes of photosynthesis, energy is transported from Rydberg atom to Rydberg atom, with each atom transmitting its energy packages to surrounding atoms, similar to a radio transmitter.

During the course of the study, the researchers measured the positions of the Rydberg atoms by examining the tiny shadow created by each Rydberg atom in the microscope image. This technique facilitated the observation of energy transport. Using a mathematical model, the scientists then showed that the atomic sea crucially influences the energy transport from Rydberg atom to Rydberg atom.

"Now we are in a good position to control the quantum system and to study the transition from diffusive transport to coherent quantum transport," said Matthias Weidemuller, one of the researchers, in a news release. "In this special form of energy transport the energy is not localized to one atom but is distributed over many atoms at the same time. In this way we hope to gain new insights into how the transformation of energy can be optimized in other synthetic systems as well, like those used in photovoltaics."

The findings are published in the journal Science.