Scientists have long suspected that the efficiency of photosynthesis depends on quantum mechanics. But they have been unable to figure out how. One mystery concerns the function of certain proteins, known as antennas, which intercept photons and channel their energy to reaction centres, where a cell converts water and carbon dioxide to oxygen and sugar. But the reaction centres can do the job themselves, so why the extra hardware? The researchers fired ultrafast, low-power laser pulses at the molecular antennas within algal cells and then measured changes in the light energy. They found that the way the antennas reacted with the photons revealed unmistakable signs of quantum mechanics.

When photons strike a molecule, they transfer energy by vibrating the molecule's electrons. But that vibration slows down rapidly if the electron is transferred to another molecule. For that reason the researchers expected that the energy from the laser could not easily be transferred from the antenna molecules to the reaction-centre molecules. Yet the experiments showed that the electron vibrations resulting from the photons striking the antennas persisted at full strength four times longer than expected due to quantum mechanics controlling the energy.