Optomechanical disk resonator in the quantum ground state of motion

TL;DR

This paper reports the first experimental achievement of preparing an optomechanical disk resonator in its quantum ground state, demonstrating sub-single phonon excitation levels through advanced cooling and spectroscopy techniques.

Contribution

It is the first to demonstrate an optomechanical disk resonator in the quantum ground state, using Brillouin sideband spectroscopy and investigating laser-induced heating effects.

Findings

Achieved phonon occupancy of 0.66±0.20 in a GHz mechanical mode

Demonstrated cooling of the resonator below one phonon

Identified laser-induced heating as a limiting factor

Abstract

Although they have enabled several advances in the field of optomechanics, optomechanical disk resonators have not yet been operated in the quantum regime. We present the first experimental demonstration of an optomechanical disk resonator prepared in the quantum ground state. With a gigahertz frequency, the mechanical breathing mode of the investigated semiconductor disk reaches a level of excitation below a single phonon when cooled in a dilution refrigerator. We quantify the phonon occupancy of the mechanical mode by performing Brillouin sideband spectroscopy: a conical optical fiber is evanescently coupled to the disk optical whispering-gallery mode, and Stokes and anti-Stokes photons scattered by phonon emission and absorption are counted on a single-photon detector. We measure a suppression of the absorption process corresponding to a phonon occupancy of $0.66\pm0.20$. We experimentally investigate the mechanisms ruling laser-induced heating, which limits the lowest measurable phonon occupancy, and notably witness an extra-cavity heating effect.