9 February 2021 Tue 4 pm

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Electromechanical phenomena on the nanometer scale attract significant attention during the last two decades. Modern nanomechanical resonators have demonstrated mechanical oscillations with extremely low damping, fine electromagnetic tuning of resonant frequencies, and have been already used as ultrasensitive mass and force quantum detectors. Such fascinating physical phenomena as the electromagnetically induced mechanical instability and ground-state cooling of the mechanical oscillations have been predicted in NEMS in the presence of incoherent dynamics of the electronic subsystem. 

The central point of the nanoelectromechanical phenomena is the origin of the electromechanical interaction.  Mostly, this interaction is caused by the presence of electrostatic or magnetostatic forces induced by stochastic fluctuations of a charge or spin localized in space. 

In this presentation, I consider a novel avenue within the research field of NEMS devices studying the mechanical instability and ground-state cooling of the mechanical oscillations induced by coherent quantum oscillations in the electronic subsystems. 

To realize this effect, we propose to use a nanoelectromechanical Andreev device based on superconducting hybrid junction, where normal and superconducting leads are bridged by a mechanically active mediator, e.g. a vibrating carbon nanotube.  Treating the carbon nanotube as a single-level quantum dot, and using a rigorous reduced density matrix analysis we obtain that in such a system the mechanical motion is coupled to the coherent Cooper pairs oscillations between two Andreev energy levels, and is controlled by stochastic incoherent tunneling of a single electron. The nontrivial interplay between these two processes results in the generation of self-sustained oscillations or cooling of the mechanical subsystem. Which one of these phenomena takes place is determined by the relative position of the single-electron energy level, and the relation between Josephson frequency and eigenfrequency of the mechanical oscillator.