Quantum electromechanics: Quantum tunneling near resonance and qubits from buckling nanoscale bars

Analyzing recent experimental results [Reulet et al., Phys. Rev. Lett. 85, 2829 (2000); Izmalkov et al., Europhys. Lett. 65, 844 (2004)], we find strikingly similar behaviors between two very different systems: 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 amplitudes, splits into two subpeaks for strong driving amplitudes. We describe this unusual behavior by considering quantum tunneling in a double well potential. Inspired by these experiments, we propose a mechanical qubit based on buckling nanoscale bars (nanobars)---a nanoelectromechanical system so small as to be quantum coherent. We consider how this nanomechanical qubit can be manipulated. A comparison between nanobars and superconducting qubits suggests several future experiments on quantum electromechanics.