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''', stated 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."
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", stated Fei Pei. "We will now focus on reducing the disturbance, so to extend the lifetime of the superposition."
The research group of Prof.dr.ir. Leo 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.
The paper. titled "A valley-spin qubit in a carbon nanotube", by Edward Laird, Fei Pei, and Leo Kouwenhoven has appeared inNature Nanotechnologyadvanced on-line publication of 28 July 2013.