Cooling of a Suspended Nanowire by an ac Josephson current

Sammanfattning: Nanoelectromechanical systems have been used for the exploration of the quantum limit of mechanical motion. There is hope that the quest for the quantum regime of these systems will shed light on fundamental questions in physics and lead to new quantum technologies. In essence, the realization of the quantum limit consists of reducing the effective temperature of the system below a certain limit. Consequently, an efficient cooling scheme that reaches the quantum ground state must be devised. It is the objective of this thesis to discuss the conditions necessary for ground state cooling of a voltage biased metallic nanowire suspended between two superconducting leads. Considering this system in the low bias regime, by using the density matrix theoretical framework it is shown that due to the transfer of energy from the mechanical vibrations of the nanowire to the electronic quasiparticle bath, ground state cooling of the nanoresonator can be achieved. The cooling is accomplished through an electromechanical coupling obtained by applying an uniform magnetic field perpendicular to the long axis of the nanobeam or by connecting the system to a gate electrode palced below the suspended nanotube.