Ground-state cooling of a mechanical oscillator by noise-interference in Andreev-reflections

Pascal Stadler, Wolfgang Belzig, Gianluca Rastelli

Published 2015-11-16Version 1

We study the active ground-state cooling of mechanical oscillator linearly coupled to the charge of a quantum dot inserted between a normal metal and a superconducting contact. Such a system can be realized e.g. by a suspended carbon nanotube quantum dot with capacitive coupling to a gate. Applying a bias-voltage and focusing on the subgap transport regime, we analyze the inelastic Andreev reflections which drive the resonator to a nonequilibrium state. For small coupling, we obtain that the vibration-assisted reflections can occur through two distinct interference paths. The interference determines the ratio between the rates for absorption and emission processes of vibrational energy quanta. We show that ground-state cooling of the mechanical oscillator can be achieved in a wide parameter range and even for many oscillator's modes simultaneously.