Scientists find quantum mechanics at work in photosynthesis

Chemists at the University of Toronto (Toronto, ON, Canada) and the University of New South Wales (Sydney, Australia) have made a major contribution to the emerging field of quantum biology, observing quantum mechanics at work in photosynthesis in marine algae.¹

"There's been a lot of excitement and speculation that nature may be using quantum mechanical practices," said Greg Scholes, a chemistry professor at the University of Toronto and the lead author of the study. "Our latest experiments show that normally functioning biological systems have the capacity to use quantum mechanics in order to optimize a process as essential to their survival as photosynthesis."

Proteins called light-harvesting complexes are used in photosynthesis to capture sunlight and funnel its energy to other proteins called reaction centers. Scholes and his colleagues isolated light-harvesting complexes from two different species of marine algae and studied their function at typical temperatures using laser-assisted 2-D electronic spectroscopy.

Light in two places at once

"We stimulated the proteins with femtosecond laser pulses to mimic the absorption of sunlight," said Scholes. "This enabled us to monitor the subsequent processes, including the movement of energy between special molecules bound in the protein, against a stop-clock. We were astonished to find clear evidence of long-lived quantum mechanical states involved in moving the energy. Our result suggests that the energy of absorbed light resides in two places at once--a quantum superposition state, or coherence--and such a state lies at the heart of quantum-mechanical theory."

Scholes noted that there are several reasons this research is of interest. "First, it means that quantum mechanical probability laws can prevail over the classical laws of kinetics in this complex biological system, even at normal temperatures," he said. "The energy can thereby flow efficiently by--counterintuitively--traversing several alternative paths through the antenna proteins simultaneously. It also raises some other potentially fascinating questions, such as, have these organisms developed quantum-mechanical strategies for light-harvesting to gain an evolutionary advantage? It suggests that algae knew about quantum mechanics nearly two billion years before humans."

The original University of Toronto press release can be found here.

REFERENCE:

1. Elisabetta Collini et al., Nature 463, 644-647 (4 February 2010) doi:10.1038/nature08811.