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July 29, 2013

Scientists realize quantum bit with a bent nanotube

One of the biggest challenges in quantum science is to build a functioning quantum bit, the basic element for the quantum computer. An important theoretical candidate for such a quantum bit is using a bent carbon nanotube. Scientists at the Delft University of Technology and the Foundation for Fundamental Research on Matter (FOM), led by FOM focus group leader Prof.dr.ir. Leo Kouwenhoven, have succeeded for the first time to create a working quantum bit using a carbon nanotube. FOM PhD student Fei Pei carried out part of the measurements. On 28 July they published their results in Nature Nanotechnology.
Figure 1. Bent carbon nano tube
vergroten Figure 1. Bent carbon nano tube
One of the biggest challenges in quantum science is to build a functioning quantum bit, the basic element for the quantum computer. An important theoretical candidate for such a quantum bit is using a bent carbon nanotube.
Credits: TU Delft
Quantum computer
Quantum computers have the advantage that they can be much faster than 'ordinary' supercomputers for various calculations. An ordinary computer bit has the value '1 'or '0', but a quantum bit uses the state of a single electron, which due to the extraordinary properties of the quantum world can take ​​ both values at the same time. "We call that a 'superposition''' says FOM PhD student Fei Pei who carried out part of the measurements. "The main problem that quantum physicists have to deal with is that the superposition can be disturbed quickly by external factors, for instance by other particles around the quantum bit."

Bent tubes
Carbon nanotubes of a few nanometers in diameter have exceptional properties that make them a very suitable material for hosting quantum bits, but so far no one could manipulate and 'read' a single electron in a nanotube. The scientists have achieved that. They were inspired by the work of colleagues from Copenhagen who showed in 2010 theoretically that the quantum state of an electron can be controlled in a bent nanotube, and carried on their own work from 2012. Back then they showed how to read the electron quantum states in a nanotube. Putting both ideas together created a 'functioning' quantum bit.

"The next challenge would be to improve the stability of this quantum bit as currently we can not maintain the superposition state long enough", said Pei. "We will now focus on reducing the disturbance, so to extend the lifetime of the superposition”.

Candidates
The research group of Kouwenhoven is focusing on a number of possible 'candidates' of a functioning and stable quantum bit. Carbon nanotube is one of the candidates. Another part of the research is focused on making a quantum bit based on the renowned Majorana particles, previously demonstrated by the same group. Further research will show which candidate is the best.

Reference
A valley-spin qubit in a carbon nanotube, Edward Laird, Fei Pei, Leo Kouwenhoven. Nature Nanotechnology advanced online publication (28 July 2013).

Fei Pei was one of the winners of the FOM Film Challenge 2012

For more information: Edward Laird, +44 (18) 65 27 37 19.