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Quantum Doughnuts Slow And Freeze Light At Will: Fast Computing And 'Slow Glass'

Date:
March 9, 2009
Source:
University of Warwick
Summary:
Researchers have found a way to use doughnuts shaped by-products of quantum dots to slow and even freeze light, opening up a wide range of possibilities from reliable and effective light-based computing to the possibility of "slow glass."

Stock image of a triangular glass prism refracting light beams. A new technique has been devised to completely freeze and release individual photons at will.
Credit: iStockphoto/Ashok Rodrigues

Research led by the University of Warwick has found a way to use doughnut shaped by-products of quantum dots to slow and even freeze light, opening up a wide range of possibilities from reliable and effective light-based computing to the possibility of "slow glass."

The key to this new research is the “exciton.” This describes 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 that has been vacated by electrons moving to a higher energy state. When an electron’s high energy state decays again, it is drawn back to the hole it is linked to and a photon is once again emitted.

That cycle usually happens very quickly, but if one could find a way to freeze or hold an exciton in place for any length of time, one could delay the reemitting of a photon and effectively slow or even freeze light.

The researchers, led by PhD researcher Andrea Fischer and Dr. Rudolf A. Roemer from the University of Warwick’s Department of Physics, looked at the possibilities presented by some tiny rings of matter accidentally made during the manufacture quantum dots. When creating these very small quantum dots of a few 10-100nm in size, physicists sometimes cause the material to splash when depositing it onto a surface, leaving not a useful dot, but a doughnut-shaped ring of material.  Though originally created by accident, these “Aharonov-Bohm nano rings” are now a source of study in their own right, and in this case seemed just the right size for enclosing an exciton. However, simply being this useful size does not, in itself, allow them to contain or hold an exciton for any length of time.

However, remarkably the Warwick led research team have found that if a combination of magnetic and electric fields is applied to these nano-rings, they can actually then simply tune the electric field to freeze an exciton in place or let it collapse and re-emit a photon.

While other researchers have used varying exotic states of matter to dramatically slow the progress of light, this is the first time a technique has been devised to completely freeze and release individual photons at will.

Dr Roemer said: “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 re-release them in sequence at a later date, thus creating an effect not unlike the concept of  “Slow Glass” first suggested by science fiction author Bob Shaw several decades ago.

The new research paper is entitled “Exciton storage in a nanoscale Aharonov-Bohm ring with electric field tuning," by University of Warwick PhD student Andrea M.Fischer, Dr Rudolf  Roemer (University of Warwick)  Vivaldo L. Campo Jr. (Universidade Federal de Sao Carlos-UFSCar, Brazil), and Mikhail E. Portnoi (University of Exeter), and has just been published in Physical Review Letters (PRL).


Story Source:

The above story is based on materials provided by University of Warwick. Note: Materials may be edited for content and length.


Journal Reference:

  1. Fischer et al. Exciton Storage in a Nanoscale Aharonov-Bohm Ring with Electric Field Tuning. Physical Review Letters, 2009; 102 (9): 096405 DOI: 10.1103/PhysRevLett.102.096405

Cite This Page:

University of Warwick. "Quantum Doughnuts Slow And Freeze Light At Will: Fast Computing And 'Slow Glass'." ScienceDaily. ScienceDaily, 9 March 2009. <www.sciencedaily.com/releases/2009/03/090309105026.htm>.
University of Warwick. (2009, March 9). Quantum Doughnuts Slow And Freeze Light At Will: Fast Computing And 'Slow Glass'. ScienceDaily. Retrieved October 22, 2014 from www.sciencedaily.com/releases/2009/03/090309105026.htm
University of Warwick. "Quantum Doughnuts Slow And Freeze Light At Will: Fast Computing And 'Slow Glass'." ScienceDaily. www.sciencedaily.com/releases/2009/03/090309105026.htm (accessed October 22, 2014).

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