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Quantum Light Beams Solve Biological Mazes

MYLES GOUGH
10 FEB 2015

Scientists in the field of quantum biology are interested in the quantum mechanical effects at play during photosynthesis, as light travels through complex matrices inside the proteins of plant cells. 

 

Understanding these effects could help engineers develop more efficient solar cells, or powerful photonic devices capable of transmitting digital information at unprecedented speeds. 

The process of photosynthesis begins when sunlight is absorbed by proteins inside an organism, where it is converted into chemical energy. But before any reaction can occur, the sunlight - or energy - must pass through a complicated network of matrices within the protein. 

As MIT Technology Review reports, these matrices are essentially “giant mazes”, and the transfer of energy across these structures “appears to occur extremely rapidly with close to 100 percent efficiency”.

Speed is the name of the game, as the energy needs to navigate through the maze before it dissipates. The question is, how does this happen?

The classical solution to the problem suggests that light explores the maze through a series of "random hops", whereby the light particles seem to jump to explore possible routes. Quantum physicist Seth Lloyd from MIT has drawn an analogy between classically behaving light particles and frogs jumping on lilypads, trying to get to the centre of a pond. They can do so eventually, but will probably take a few wrong turns along the way. This process, therefore, is considered too slow and results in too much lost energy.

As such, researchers have suspected quantum processes are involved in some capacity. One idea suggests the lightwaves can take advantage of quantum mechanical properties to rapidly navigate the maze by exploring different routes simultaneously. Lloyd compares this behaviour to a circular wave, beginning at the edge of the lily pond, and propagating inward in all directions to the centre.

"But it turns out that wavelike transport is not always the best strategy," writes Lloyd for PBS. "To understand why, suppose that the lilypond is full of rocks sticking up out of the water. As the wave moves through the pond, it scatters off the rocks. As a result, the wave never reaches the middle of the pond, which remains calm and protected. This is a phenomenon called destructive interference."

It is now thought that the process involves a combination of classical and quantum effects.

A team of Italian researchers, led by Filippo Caruso at the University of Florence, has now demonstrated this hybrid effect at work for the first time. Their work has provided the first experimental evidence showing that a hybrid system significantly outperforms a purely quantum system. 

The team at MIT Technology Review explains how the experiment was carried out:

“These guys make their maze from a network of waveguides laser machined into a transparent slab. When the waveguides in this array are close together, the light can jump from one to another in a purely quantum process. However, if the waveguides are slightly further apart, the quantum process breaks down, introducing classical noise that forces the system to behave as a hybrid with both quantum and classical properties.”

The team created 24 different mazes with subtle differences, and tested the performance of hybrid navigation versus quantum navigation. 

“We theoretically demonstrate that an optimal mixing of classical and quantum dynamics leads to a remarkably efficient transmission of energy/information from the input to the exit door of a generic maze” the researchers wrote.

“For large enough maze size this leads to a remarkably high enhancement of more than five order of magnitudes in the transfer efficiency with respect to both the classical and purely quantum limits.”

Their paper “Fast Escape from Quantum Mazes in Integrated Photonics” was published online at arXiv.org.

Sources: PBS, MIT Technology Review