Posted: May 6, 2010

Scientists climb the quantum ladder

(Nanowerk News) An EU-funded team of scientists from Cardiff University in the UK has successfully fired photons (light particles) into a small tower of semiconducting material. The work could eventually lead to the development of faster computers. The research is an outcome of the CUSMEQ ('Coherent ultra-fast spectroscopy and manipulation of excitonic Q-bits') project, funded under the People Programme of the Seventh Framework Programme (FP7) with support totalling almost EUR 179 000. CUSMEQ investigated the coherent, ultra-fast spectroscopy and manipulation of individual excitonic states confined within a semiconductor quantum dot. The results of the study were recently presented in the journal Nature Materials.
The scientists, from the university's School of Physics and Astronomy, said a photon collides with an electron confined in a smaller structure within the tower. Before the light particles re-emerge, they oscillate for a short time between the states of light and matter.
'Marrying single quanta of light and matter is conceptually and technologically demanding. It can for example be accomplished by embedding an exciton trapped in a quantum dot inside an optical microcavity, in which the photon field is confined within a small mode volume,' the authors write in their paper. 'As a result, a quantum of optical excitation oscillates between light and matter before its leakage and dissipation into the outside world.
The research team performed this test by using individual and pairs of photons. They explain that photon pairs could boost the frequency of the oscillation between light and matter over individual photons. The results of their study concur with studies that made theoretical predictions nearly a half century ago.
The Cardiff team used a semiconductor tube a mere 1.8 micrometres (1 micrometre is a thousandth of a millimetre) in diameter and kept the temperature at around -263ºC. The photons were trapped inside the tube for some 10 picoseconds (1 picoseconds being 1 trillionth of a second).
Information and communications technology (ICT) will be impacted by these latest findings in a good way. The researchers said the potential to construct logical systems based on the interactions of these particles, what experts call quantum computing, is growing. The upshot of such a development is that processing would become more efficient since the particles move at much faster rates and expend less energy than conventional electronic computer components.
'This interaction can produce a steady stream of photons, and can also be the basis for single photon logic — which requires the minimum amount of energy to do logic,' explained Professor Wolfgang Langbein of the School of Physics and Astronomy. 'In the long term, there are implications in a number of areas, including computing, telecommunications and cryptography devices,' he added.
There are, however, some technical glitches that the researchers must overcome. Professor Langbein commented: 'To use this technology in real computing devices will take a significant improvement of the low-temperature properties and ideally its translation to room temperature. At the moment we have no clear concept how to do this — but it is not impossible.'
Source: European Commission