Published by the Students of Johns Hopkins since 1896
February 26, 2024

Scientists harness photosynthesis

By BARBARA HOLT | May 9, 2013

One of the modern world’s biggest concerns today is the current energy crisis.  Globally, scientists and engineers are searching to find and working to develop new alternative energy sources to replace our dwindling fossil fuel reserves.  In response, we’ve turned to wind-power, hydro-power, ethanol and many more green initiatives.  Yet, nature’s most powerful energy source has always been the sun.  Thus far, solar energy technology has not shown much promise in yielding practical and efficient results to meet today’s energy demands.  However, quantum biologists may have finally found a way to harness the sun’s vast energy potential — by mimicking plants.

Most of us are familiar with the photosynthesis cycle of plants, which converts light energy to chemical energy for a plant’s use.  Quantum biologists have recently uncovered quantum physics’ role in this process, and on April 19, researchers from University of Chicago published a paper in Science, which reported the creation of a new synthetic compound to imitate plant photosynthesis on a quantum level.

Central to this discovery is quantum superposition.  According to quantum mechanics, every particle in the universe exists in every possible state at once.  However, whenever one attempts to measure the properties or state of the particle, the particle will correspond to only one configuration of itself.

While no one is advocating animal cruelty by any means, this is analogous to the enduring Schrodinger’s cat setup.  Toxic gas is released into a box with Schrodinger’s cat.  Within the box the cat may be either alive or dead, but until someone opens the box and observes the cat it exists in both states.

Greg Engel, a chemistry professor at University of Chicago and lead researcher, demonstrated that the particular positions or configurations of light particles may play a role in the efficiency of their light energy transfer.  Engel may have discovered the reason plant photosynthesis results in virtually perfect light-harvesting.

Light-absorbing molecules effectively have “biological air traffic control towers” in the form of photosynthetic antennae.  Proteins within the plant’s absorbing molecules are organized into arrays by the photosynthetic antennae.  This orderly arrangement enables the absorbed light to achieve quantum coherence, or essentially “match” quantum configurations, guiding the light energy quickly and efficiently to the plant’s reaction center (where the light energy to chemical energy conversion takes place).

These “matching” superpositions are held for what is considered an extraordinarily long time in the quantum realm — several femtoseconds (or millionths of billionths of a second).

Quantum coherence between particles allows each particle to explore all possible routes to the plant’s reaction center and then pick the quickest route.  This foresight from the light particles’ quantum collaboration greatly increases energy capture, as the light energy does not have to randomly explore each possible path, but may skip ahead to the fastest one.

By linking together molecules of fluorescin, a fluorescent green dye, and hitting the molecules successively with femtosecond laser pulses from three different directions, Engel’s lab was able to artificially recreate this phenomenon.  The fluorescin glows when excited by the lasers, showing the flow and movement of energy with each glowing pulse.  Engel filmed this movement and measured the signal oscillations, or the “quantum beat.”

When various light energies are all held at the same quantum configuration, they produce a distinctive quantum beat.  Dugan Hayes, a co-author of the paper, compared this phenomenon to the interference created when two different instruments play the same note.

This exciting discovery may yet produce synthetic light-harvesting systems and speed us towards a highly green and energy-efficient future.

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