09 March 2009
Doughnuts help to slow light
Research led by the University of Warwick has found a way to use doughnut shaped by products of quantum dot production to slow or even freeze light.
According to the researchers, this opens a range of possibilities; from light based computing to the possibility of ‘slow glass’.
The key to this research is the exciton – the pairing of an electron that has been kicked into a higher energy state by a photon, with a hole or gap it (or another electron) leaves within the shell or orbit around the nucleus of an atom.
Despite its new high energy state, the electron remains paired with one of the holes or positions vacated by electrons moving to a higher energy state. When an electron’s high energy state decays, it is drawn back to the hole to which it is linked and a photon is emitted.
That cycle usually happens very quickly, but if a way could be found to freeze or hold an exciton in place, say the researchers, one could delay the reemitting of a photon and effectively slow or even freeze light.
The researchers, led by Andrea Fischer and Dr Rudolf Roemer from the University’s Department of Physics, looked at the possibilities presented by tiny rings of matter accidentally made during the manufacture quantum dots. When creating quantum dots, physicists some times cause the material to splash when depositing it onto a surface. This leaves a doughnut shaped ring of material. Though originally created by accident, ‘Aharonov-Bohm nano rings’ are now a source of study and appear to be the right size for enclosing an exciton.
The research team found that if a combination of magnetic and electric fields is applied to these nano rings, they can freeze an exciton in place or let it collapse and re emit a photon.
According to Dr Roemer: “This has significant implications for the development of light based computing, which would require an effective and reliable mechanism such as this to manipulate light.”
The technique could also be used to develop a ‘buffer’ of incoming photons, which could be released in sequence at a later point, creating an effect not unlike the concept of Slow Glass, first suggested by science fiction author Bob Shaw several decades ago.
Author
Graham Pitcher
Supporting Information
Websites
http://www.warwick.ac.uk
Companies
University of Warwick
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