Ultrafast technique unlocks design principles of quantum biology

Apr 19, 2013
University of Chicago researchers have created a synthetic compound that mimics the complex quantum dynamics observed in photosynthesis. The compound may enable fundamentally new routes to creative solar light harvesting technologies. Credit: Graham Griffin

University of Chicago researchers have created a synthetic compound that mimics the complex quantum dynamics observed in photosynthesis and may enable fundamentally new routes to creating solar-energy technologies. Engineering quantum effects into synthetic light-harvesting devices is not only possible, but also easier than anyone expected, the researchers report in the April 18 edition of Science Express.

The researchers have engineered small molecules that support long-lived quantum coherences. Coherences are the macroscopically observable behavior of quantum superpositions. Superpositions are a fundamental quantum mechanical concept, exemplified by the classic Schrodinger's Cat thought experiment, in which a single such as an electron occupies more than one state simultaneously.

are generally negligible in large, hot, disordered systems. Nevertheless, the recent ultrafast spectroscopy experiments in UChicago chemistry Prof. Greg Engel's laboratory have shown that quantum superpositions may play a role in the near perfect of photosynthetic light harvesting, even at physiological temperatures.

Photosynthetic antennae – the proteins that organize chlorophylls and other light-absorbing molecules in plants and bacteria – support superpositions that survive for anomalously long times. Many researchers have proposed that organisms have evolved a means of protecting these superpositions. The result: improved efficiency in transferring from absorbed sunlight to the parts of the cell that convert solar energy to chemical energy. The newly reported results demonstrate that his particular manifestation of can be engineered into man-made compounds.

University of Chicago researchers have created synthetic molecules that support-long-lived quantum coherence at room temperature. Pictured (l-r) are postdoctoral scholar Graham Griffin, professor Greg Engel and graduate student Dugan Hayes. Credit: Tom Jarvis

The researchers modified fluorescein – the same molecule once used to dye the Chicago River green for St. Patrick's Day – and then linked different pairs of these dyes together using a rigid bridging structure. The resulting molecules were able to recreate the important properties of chlorophyll molecules in photosynthetic systems that cause coherences to persist for tens of femtoseconds at room temperature.

"That may not sound like a very long time - a femtosecond is a millionth of a billionth of a second," said study co-author Dugan Hayes, a UChicago graduate student in chemistry. "But the movement of excitations through these systems also occurs on this ultrafast timescale, meaning that these quantum superpositions can play an important role in energy transfer."

To detect evidence of long-lived superpositions, the researchers created a movie of energy flow in the molecules using highly engineered laboratories and state-of-the-art femtosecond laser systems. Three precisely controlled laser pulses are directed into the sample, causing it to emit an optical signal that is captured and directed into a camera.

By scanning the time delays between the arriving laser pulses, the researchers create a movie of energy flow in the system, encoded as a series two-dimensional spectra. Each two-dimensional spectrum is a single frame of the movie, and contains information about where energy resides in the system and what pathways it has followed to get there.

These movies show relaxation from high energy states toward lower energy states as time proceeds, as well as oscillating signals in very specific regions of the signal, or quantum beats. "Quantum beats are the signature of quantum coherence, arising from the interference between the different energetic states in the superposition, similar to the beating heard when two instruments that are slightly out of tune with each other try to play the same note," Hayes explained.

Computer simulations have shown that quantum coherences work in photosynthetic to prevent excitations from getting trapped on their way to the reaction center, where the conversion to begins. In one interpretation, as the excitation moves through the antenna, it remains in a superposition of all possible paths at once, making it inevitable that it proceeds down the proper path. "Until these coherences were observed in synthetic systems, it remained dubious that such a complex phenomenon could be recreated outside of nature," Hayes said.

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EyeNStein
2.6 / 5 (5) Apr 19, 2013
Excellent article. Well applied science. AND humility not salesmanship and hype!
May indeed be important for future solar energy capture systems.
Someone employ these guys immediately!
vacuum-mechanics
1 / 5 (4) Apr 19, 2013
The researchers have engineered small molecules that support long-lived quantum coherences. Coherences are the macroscopically observable behavior of quantum superpositions. Superpositions are a fundamental quantum mechanical concept, exemplified by the classic Schrodinger's Cat thought experiment, in which a single quantum particle such as an electron occupies more than one state simultaneously.

This seems to be a advance research in quantum mechanics, unfortunately we still cannot understand its basic foundation such as how quantum particle like electron could act as wave and make the superposition mentioned! Maybe this physical idea could help…
http://www.vacuum...17〈=en
Tektrix
not rated yet Apr 19, 2013
Such a sublime and beautiful thing this is. The most efficient path is taken by virtue of the a priori eigenstate that maps the lowest cost to the system. An exemplary case where optimum gains are determined not by how much you have, but by how little you need.
ValeriaT
1 / 5 (2) Apr 19, 2013
The pigment array in thylakoid lamellas i.e. quantasomes appear pretty similar to quantum dots arrays. Each quantasome contains about 230 to 300 chlorophyll molecules and they're regularly spaced in 150 x 180 A lattice in similar way, like the quantum vortices in superconductors. All the molecules in each of these photo-synthetic units are spaced and oriented in such a way, captured photons are transferred from molecule to molecule by inductive resonance and the energy absorbed is transferred to as exciton.

Experiments have demonstrated though, that the presence of the quantasome particles in chloroplast membrane is not a necessary condition for photoreduction activity of chloroplasts In prokaryotes pigments are distributed uniformly on or in the thylakoid lamellae and they do work with only 7% lower quantum efficiency [J. Mol. Biol., 27, 323 (1967)].
ValeriaT
1 / 5 (3) Apr 19, 2013
May indeed be important for future solar energy capture systems
I seriously doubt it. Whole the solar cell research is essentially useless - we are still using the technologies developed before thirty years for cosmic flights, just some materials were replaced with cheaper ones. Why? Because every introduction of exciton/hot electron collectors and quantum dots, pyramids and nanotubes, etc.. increases the efficiency mildly, but it increases the production cost and ruins the life-time of such modified cells. In particular, the nanotechnologies are of large surface area and they're prone to photooxidation and photo-asisted bleaching and corrosion. The sunlight effectively destroys most of organic molecules. How is it possible, the plants are utilizing delicate structures and quantum effects, after then? Well, quite easily - they're rebuilding, repairing them and recycling them continuously. Until we will not apply it in solar cells, we will always trade the efficiency for lifetime.
EyeNStein
1 / 5 (3) Apr 20, 2013
@ValeriaT
Why so pessimistic? This is an excellent example of foundational science.
Applied structural chemistry, applied quantum theory and femtosecond imaging to test and prove the theory.
I agree this isn't immediately applicable nor massively efficient but who knows at this stage where their methodology could lead to. Later, add some synthetic biology into this scientific mix and medicines or fuels could result from better understood synthetic processes powered by light.
ValeriaT
1 / 5 (2) Apr 20, 2013
Why so pessimistic? This is an excellent example of foundational science.
This is the realism. You should know, we cannot be better than the products of four billions years standing evolution. Not to say about actual utilization of solar technology, which is unreliable and it requires transport and storage of energy. The cold fusion will always beat it at place.

What these researching are doing is the development of artificial plants - although they could simply grow them already - just because we are paying them for this research. If you will put a money systematically into single pile inside of human society, a strange things will happen there after while.