Ground-State Cooling of a Mechanical Oscillator by Interference in Andreev Reflection

TL;DR

This paper demonstrates how interference effects in Andreev reflections can be harnessed to cool a mechanical oscillator to its ground state, with potential for simultaneous or selective mode cooling.

Contribution

It introduces a novel mechanism for ground-state cooling via interference in Andreev reflections in a quantum dot system.

Findings

Ground-state cooling achievable for multiple modes.

Interference controls the balance of vibrational energy exchange.

Cooling depends on tunable coupling to the superconductor.

Abstract

We study the ground-state cooling of a 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 a capacitive coupling to a gate contact. 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 vibration-assisted reflections can occur through two distinct interference paths. The interference determines the ratio between the rates of absorption and emission of vibrational energy quanta. We show that ground-state cooling of the mechanical oscillator can be achieved for many of the oscillator's modes simultaneously or for single modes selectively, depending on the experimentally tunable coupling to the superconductor.