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Boffins build 'slow glass' light-trapping nanodoughnut

Exciton in tight ring = fast photonic computing?

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Warwickshire boffins believe they may be on the track of science-fiction "slow glass", through which light might take a long time to travel. The scientists think that such light-storing materials might be fashioned using excitons mounted inside unfeasibly tiny "quantum doughnuts".

In essence it seems that an exciton is an electron which has been jazzed up a bit energy-wise by absorbing a photon of light. The idea is that if you could prevent such excitons immediately re-emitting their photons and so turning back into electrons at once as they normally do, you could effectively store, or "freeze" light.

Such technology was imagined by renowned sci-fi scribe Robert Shaw in his novel Other Days, Other Eyes and its precursor works. "Slow Glass", through which light would take hours, days or years to travel, was used for many things in the book: stored daylight offered free lighting, for instance. (The omnipresence of slow-glass lights also delivered an equivalent of a CCTV panopticon, as images of anything happening within view of a pane of slow glass would later be visible on its other side.)

According to Warwickshire physicists Andrea Fischer and Rudolf A. Roemer, excitons - properly handled - could offer something on these lines, and might also be extremely handy in light-based (photonic) computing. With electronics approaching its limits, many researchers believe that photonics could deliver the next wave of big performance increases.

Normally an exciton, fairly uselessly, simply releases its photon almost at once. But Fischer and Roemer, trying out notions one day in the lab, decided to try slotting excitons into some quantum nano-doughnuts they had lying around.

Such "Aharonov-Bohm nano rings" were originally created as a by-product of manufacturing comparatively humdrum quantum dots. It seems that sometimes even the most skilful boffin, knocking out a batch of quantodots in a hurry, will inadvertently splash the material onto the receiving surface too hard and make a doughnut rather than a contiguous nano-blob dot.

Fischer and Roemer decided to slot an exciton into the middle of such a nano-ring, in the 10-100 nm size range. That in itself - as one would naturally expect - achieved nothing. But the addition of "a combination of magnetic and electric fields" makes it possible to trap the slippery exciton in one's unfeasibly minuscule quantum ring, at which point it is entirely at one's bidding. The exciton can then be made to hold onto its photon, "freezing" it in place, or collapse back in electronhood and emit the light on command.

"This has significant implications for the development of light based computing," says Roemer.

Though other scientists have slowed light down using various techniques which might also be significant in the possible future wave of photonic IT, Roemer and Fischer consider that theirs is the first which properly locks a photon down for release on demand.

The Warwickshire brainboxes, allied with others, publish their paper Exciton storage in a nanoscale Aharonov-Bohm ring with electric field tuning here (subscription required). ®

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