Science Literature

"Photosynthetic complexes are exquisitely tuned to capture solar light efficiently, and then transmit the excitation energy to reaction centres, where long term energy storage is initiated." The problem has been one of understanding how 95%+ efficiencies are possible in a natural system.
The photosynthetic apparatus is constructed so that adjacent chlorophyll molecules have different energy levels. "When light shines on one of these molecules, an electron is momentarily excited before passing its energy over to a nearby molecule with a slightly lower energy level. In this way energy can flow "downhill" from energy level to energy level until it reaches the crucial "reaction centre" where the actual photosynthesis occurs. Scientists had assumed that the energy moves downhill in a "random walk", which is essentially an incoherent "hopping" between energy levels." But this mechanism does not yield the "extreme efficiency" of photosynthesis.
Researchers in the US have "discovered regular variations of signal that sustained for hundreds of femtoseconds, which the physicists interpreted as "quantum beats" coherently linking all the energy levels together." This "quantum trickery" has an analogy in "Grover's algorithm" (proposed in 1997) which determines "the fastest possible search of an unsorted database in quantum computation." With this mechanism, "vast areas of phase space can be sampled effectively to find the most efficient path for energy transfer."
Those involved in a quest for simplicity in the machinery of molecular biology are not having a very happy time. The story being uncovered is one of complexity in the details, as Michael Behe demonstrated in Darwin's Black Box. Knowing that quantum paths have been used in photosynthesis, the "primary energy source for almost all life on Earth", provides yet more grounds for making design inferences.

Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems
Gregory S. Engel, Tessa R. Calhoun, Elizabeth L. Read, Tae-Kyu Ahn, Tomas Mancal, Yuan-Chung Cheng, Robert E. Blankenship and Graham R. Fleming.
Nature 446, 782-786 (12 April 2007) | doi:10.1038/nature05678

Abstract: Photosynthetic complexes are exquisitely tuned to capture solar light efficiently, and then transmit the excitation energy to reaction centres, where long term energy storage is initiated. The energy transfer mechanism is often described by semiclassical models that invoke 'hopping' of excited-state populations along discrete energy levels1, 2. Two-dimensional Fourier transform electronic spectroscopy3, 4, 5 has mapped6 these energy levels and their coupling in the Fenna-Matthews-Olson (FMO) bacteriochlorophyll complex, which is found in green sulphur bacteria and acts as an energy 'wire' connecting a large peripheral light-harvesting antenna, the chlorosome, to the reaction centre7, 8, 9. The spectroscopic data clearly document the dependence of the dominant energy transport pathways on the spatial properties of the excited-state wavefunctions of the whole bacteriochlorophyll complex6, 10. But the intricate dynamics of quantum coherence, which has no classical analogue, was largely neglected in the analyses-even though electronic energy transfer involving oscillatory populations of donors and acceptors was first discussed more than 70 years ago11, and electronic quantum beats arising from quantum coherence in photosynthetic complexes have been predicted12, 13 and indirectly observed14. Here we extend previous two-dimensional electronic spectroscopy investigations of the FMO bacteriochlorophyll complex, and obtain direct evidence for remarkably long-lived electronic quantum coherence playing an important part in energy transfer processes within this system. The quantum coherence manifests itself in characteristic, directly observable quantum beating signals among the excitons within the Chlorobium tepidum FMO complex at 77 K. This wavelike characteristic of the energy transfer within the photosynthetic complex can explain its extreme efficiency, in that it allows the complexes to sample vast areas of phase space to find the most efficient path.

See also:

Making photosynthesis tick (Editor's summary, Nature 446,(12 April 2007).

Sension, R.J. Quantum path to photosynthesis, Nature 446, 782-786 (12 April 2007) | doi:10.1038/446740a
Knowing how plants and bacteria harvest light for photosynthesis so efficiently could provide a clean solution to mankind's energy requirements. The secret, it seems, may be the coherent application of quantum principles.

Cartwright, J. Photosynthesis takes a leaf out of the quantum book, PhysicsWeb, April 13 2007.
Quantum computers and blades of grass have more in common than you might think. Physicists in the US have shown that electrons involved in photosynthesis reactions "sample" different energy-level routes in much the same way quantum-computer algorithms can - at least in theory - quickly search through unsorted databases. The researchers claim that the discovery could explain how photosynthesis can proceed at efficiencies unparalleled in manmade solar cells.