Optomechanical sideband cooling of a micromechanical oscillator close to the quantum ground state

TL;DR

This paper demonstrates near-ground-state cooling of a 70-MHz micromechanical oscillator using optomechanical sideband cooling, achieving occupancy below 10 quanta and highlighting reduced damping from defect states.

Contribution

It introduces a method to pre-cool a micromechanical oscillator close to its quantum ground state and reduces defect-induced damping, with independent thermometry for excess heating.

Findings

Pre-cooled oscillator to below 200 quanta using 3He gas.

Achieved average occupancy of 9±1 quanta with sideband cooling.

Oscillator spends about 10% of the time in its ground state.

Abstract

Cooling a mesoscopic mechanical oscillator to its quantum ground state is elementary for the preparation and control of low entropy quantum states of large scale objects. Here, we pre-cool a 70-MHz micromechanical silica oscillator to an occupancy below 200 quanta by thermalizing it with a 600-mK cold 3He gas. Two-level system induced damping via structural defect states is shown to be strongly reduced, and simultaneously serves as novel thermometry method to independently quantify excess heating due to the cooling laser. We demonstrate that dynamical backaction sideband cooling can reduce the average occupancy to 9+-1 quanta, implying that the mechanical oscillator can be found (10+- 1)% of the time in its quantum ground state.