“How your average leaf transfers energy from one molecular system to another is nothing short of a miracle. Quantum coherence is key to the efficiency, with the system sampling all the energy pathways all at once. And the way nanotechnology is heading, we could copy this with the right materials... .” This quote comes not from a grant proposal, but from Ian McEwan's latest novel Solar (Jonathan Cape, 2010), in which a young researcher at the fictional National Centre for Renewable Energy in the UK proposes to use quantum effects to improve the efficiency of photocatalytic water splitting, ushering in the vaunted hydrogen economy. As the 'McGuffin' for a tragicomedy set against the backdrop of energy research and global warming, it is an impressively well motivated idea.

McEwan is renowned for doing his scientific homework, and here he has evidently come across recent work1,2 demonstrating that quantum coherence is used to assist energy transfer in the antennae of the light-harvesting complex of photosystem II (PS II). This protein–pigment complex converts light absorption into electron flow, initiating the photoelectrochemical processes that split water and drive the synthesis of the energy-storage molecule adenosine triphosphate (ATP).

Quantum coherence refers here to the way that electronically excited quantum states of the pigment chromophores called excitons maintain a correlated phase relationship for long enough to assist transfer of the excitation energy towards the reaction centre, where an electron is ejected from chlorophyll. These quantum dynamics depend on the precise nanoscale arrangement of the pigment molecules.

Quantum coherence is precisely what is sought in quantum computers, as it allows the creation of superposition states of quantum bits (qubits) that provide extra channels for storing and processing information, which are not available to classical devices. But in the technological prototypes produced so far, quantum coherence typically requires the physical carriers of qubits — electromagnetically trapped atoms or ions, for example — to be kept ultracold. Otherwise, interactions with the disorderly environment quickly destroy the coherence. Yet remarkably, in PS II coherence is maintained at room temperature for long enough to make the efficiency of the energy-transfer process almost perfect.

That, at least, is the assumption, for the earlier experiments were done only at cryogenic temperatures (77 K). But now Engel and co-workers have shown that at physiological temperatures (277 K), the coherence does indeed survive for at least 300 fs, which is long enough to be biologically relevant3. Meanwhile, Fleming et al. have shown that polarized electronic spectroscopy can be used to map out the excitation energies of each chromophore in the antenna array, determining the spatial, orientational and energetic factors that enable the quantum effect to operate so well4.

Can this trick really be enlisted for solar-energy generation? Energy conversion efficiency is certainly high on the agenda for photovoltaics — very recently, a new record efficiency was claimed for one class of thin-film cell using layered semiconductors5. And mimicking photosynthesis in artificial nanostructures has a strong pedigree in solar-cell technology6. McEwan won't be the first to spot the technological potential, but it's a fair bet he has more readers than Nature.