Using carbon nanotubes as qubits for quantum computers

March 26, 2013

Like a guitar string, nanotubes (black) can be clamped and excited to vibrate. An electric field (electrodes: blue) ensures that two of the many possible states can be selectively addressed. (Credit: M.J. Hartmann, TUM)

A study by physicists at the Technical University of Munich (TUM) has shown how nanotubes can store information in the form of vibrations.

Using quantum mechanical phenomena, computers could be much more powerful than their classical digital predecessors.

Up to now, researchers have experimented primarily with electrically charged particles. But because nanomechanical devices are not charged, they are much less sensitive to electrical interference.

To date most systems are based on electrically charged particles that are held in an “electromagnetic trap.” A disadvantage of these systems is that they are very sensitive to electromagnetic interference and therefore need extensive shielding. Physicists at TUM have now found a way for information to be stored and quantum mechanically processed in mechanical vibrations.

A carbon nanotube that is clamped at both ends can be excited to oscillate. Like a guitar string, it vibrates more than a million time, allowing information to be retained for up to one second.

Since such a string oscillates among many physically equivalent states, the physicists resorted to a trick: an electric field in the vicinity of the nanotube ensures that two of these states can be selectively addressed. The information can then be written and read optoelectronically.

“Our concept is based on available technology,” says Michael Hartmann, head of the Emmy Noether research group Quantum Optics and Quantum Dynamics at TUM. “It could take us a step closer to the realization of a quantum computer.”

The research was supported by the German Research Council (DFG).