  Analyzing recent experimental results, we find similar behaviors and a deep
analogy between three-junction superconducting qubits and suspended carbon
nanotubes. When these different systems are ac-driven near their resonances,
the resonance single-peak, observed at weak driving, splits into two sub-peaks
(Fig. 1) when the driving increases. This unusual behavior can be explained by
considering quantum tunneling in a double well potential for both systems.
Inspired by these experiments, we propose a mechanical qubit based on buckling
nanobars--a NEMS so small as to be quantum coherent.
  To establish buckling nanobars as legitimate candidates for qubits, we
calculate the effective buckling potential that produces the two-level system
and identify the tunnel coupling between the two local states. We propose
different designs of nanomechanical qubits and describe how they can be
manipulated. Also, we outline possible decoherence channels and detection
schemes. A comparison between nanobars and well studied superconducting qubits
suggests several future experiments on quantum electromechanics.

Mesoscale and Nanoscale Physics