Boffins play ping-pong with single electron
Sounds more like pinball to us, but they're the boffins
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Researchers at Cambridge University have managed to bat an electron back and forth along a wire in a high-tech game of ping-pong that could help out with quantum computing.
The findings, published in Nature, showed the boffins were able to exercise a high level of control over the path of an electron in an electronic circuit.
Taking firm control of an electron in a circuit is not easy to do, as usually an electron carrying a current along a wire takes a complicated zigzag path instead of going straight to the other end. When the electron is carrying information, these are annoying detours that can cause it to drop any information it might be carrying or, in science-speak, the quantum state loses coherence.
The Cambridge Uni scientists trapped their electron in a "quantum dot" – a small hole in the surface of a piece of gallium arsenide. They then created a channel of a higher energy than surrounding electrons, which led to another dot that was empty. A burst of sound carries the electron from one dot to the next on an acoustic wave, and another burst sends it back again.
The researchers got rallies of up to 60 shots going before, as they intriguingly put it, "anything goes wrong".
"There is a lot of work going on worldwide to make this new type of computer, which may solve certain complex problems much faster than classical computers. However, little effort has yet been put into connecting up different components, such as processor and memory," said the top boffin from the Semiconductor Physics Group, Chris Ford.
"Although our experiments do not yet show that electrons 'remember' their quantum state, this is likely to be the case. This would make the method of transfer a candidate for moving quantum bits of information (qubits) around a quantum circuit, in a quantum computer." ®
COMMENTS
You're right that the speed that electrons move at in a normal wire is pretty slow - for a DC current they move at what's called the drift velocity, which for most metals is something like a few mm per hour if I remember correctly. Here the electrons are moving at about the speed of sound (2.7 km/s in gallium arsenide, give or take)
The thing is, these single-electron devices operate in a totally different regime to normal electrical devices. The idea is to use the quantum properties of a few electrons (probably their spin, though that's not looked at in this experiment) to form the building blocks of a quantum computer. And the sort of technique demonstrated here could be useful in moving those building blocks around - think, for example, of transferring info between a CPU and RAM in a normal computer.
It's not the burst of sound itself which carries the electron: these devices work because gallium arsenide is piezoelectric (ie if you deform it slightly, it produces an electric field). The deformation of the crystal due to the sound wave thus leads to a travelling electrical wave which travels along at approximately the speed of sound, and that's what moves the electron backwards and forwards.
link to paper
A freely-available version of the paper is at http://arxiv.org/abs/1107.3886 for anyone interested
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