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The smallest vibration sensor in the quantum world

15 March 2013

Carbon nanotubes and magnetic molecules are being considered as possible building blocks of future nano-electronic systems.

The spin of a molecule (orange) changes and deforms the nanotube (black) mounted between two electrodes (gold) (igure: C. Grupe/KIT)
The spin of a molecule (orange) changes and deforms the nanotube (black) mounted between two electrodes (gold) (igure: C. Grupe/KIT)

Researchers at Karlsruhe Institute of Technology (KIT) and colleagues from Grenoble and Strasbourg have found a way to combine both these components at the atomic scale to build a quantum mechanical system with novel properties. 

In their experiment the researchers used a carbon nanotube, mounted between two metal electrodes and spanning a distance of about 1µm, which was able to vibrate mechanically. They then applied an organic molecule with magnetic spin due to an incorporated metal atom. This spin was oriented in an external magnetic field.

“In this setup, we demonstrated that the vibrations of the tube are influenced directly when the spin flips parallel or antiparallel to the magnetic field,” explains Mario Ruben, head of the working group at KIT. When the spin changes, the resulting recoil is transferred to the carbon nanotube and the latter starts to vibrate. Vibration changes the atomic distances of the tube and, hence, its conductance that is used as a measure of motion.

The strong interaction between a magnetic spin and mechanical vibration opens up interesting applications such as determining the masses of individual molecules and the measurement of magnetic forces at nano scale. Use as a quantum bit in a quantum computer might also be feasible, say the researchers. 

A wave propagating along a carbon nanotube is shown in this illustrative video clip.

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