Nanomechanical Qubit Could Be Highly Stable

(PhysicsWorld) A quantum bit based on a vibrating carbon nanotube and a pair of quantum dots could be unusually resistant to noise. Although the new nanomechanical qubit is currently at the proposal stage, calculations by Fabio Pistolesi of the French National Centre for Scientific Research (CNRS) at the University of Bordeaux and colleagues in the US and Spain indicate that its so-called “decoherence time” – a measure of how long fragile quantum information can survive in a noisy environment – would be remarkably long, making it an attractive platform for quantum computing.
In the proposed nanomechanical qubit, a suspended carbon nanotube acts as a resonator, and its vibrations couple to a double quantum dot that forms within the nanotube itself. This double quantum dot has discrete electronic states, and the coupling between them allows the resonator to become strongly anharmonic – that is, the frequency of its oscillations depend strongly on their amplitude. In such an oscillator, even the tiniest change in the resonator’s amplitude is easily detected. This amplitude, Pistolesi explains, can then be used to store quantum information.
The qubits in such a platform would stay coherent for a long time because the information is stored in their mechanical oscillation amplitude and the oscillator can perform millions of oscillations before it starts to become damped.