– I’ve been watching this story for a year or more since I saw the first reference to this new work.
– Fascinating stuff. If something as simple as Chlorophyll can employ quantum computing to search multiple paths at simultaneously, then is it so far out to imagine that the mechanisms employed by an thinking brain may do the same?
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WHILE physicists struggle to get quantum computers to function at cryogenic temperatures, other researchers are saying that humble algae and bacteria may have been performing quantum calculations at life-friendly temperatures for billions of years.
The evidence comes from a study of how energy travels across the light-harvesting molecules involved in photosynthesis. The work has culminated this week in the extraordinary announcement that these molecules in a marine alga may exploit quantum processes at room temperature to transfer energy without loss. Physicists had previously ruled out quantum processes, arguing that they could not persist for long enough at such temperatures to achieve anything useful.
Photosynthesis starts when large light-harvesting structures called antennas capture photons. In the alga called Chroomonas CCMP270, these antennas have eight pigment molecules woven into a larger protein structure, with different pigments absorbing light from different parts of the spectrum. The energy of the photons then travels across the antenna to a part of the cell where it is used to make chemical fuel.
The route the energy takes as it jumps across these large molecules is important because longer journeys could lead to losses. In classical physics, the energy can only work its way across the molecules randomly. “Normal energy transfer theory tells us that energy hops from molecule to molecule in a random walk, like the path taken home from the bar by a drunken sailor,” says Gregory Scholes at the University of Toronto, Canada, one of the co-authors of the paper published in Nature this week (DOI: 10.1038/nature08811).
But Scholes and his colleagues have found that the energy-routeing mechanism may actually be highly efficient. The evidence comes from the behaviour of pigment molecules at the centre of the Chroomonas antenna. The team first excited two of these molecules with a brief laser pulse, causing electrons in the pigment molecules to jump into a quantum superposition of excited states. When this superposition collapses, it emits photons of slightly different wavelengths which combine to form an interference pattern. By studying this pattern in the emitted light, the team can work out the details of the quantum superposition that created it.
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