Laser cooling of a Planck mass object close to the quantum ground state

Quantum mechanics has so far not been tested for mechanical objects at the scale of the Planck mass \(\sqrt{\hbar c/ G} \simeq 22\,\mu\mathrm{g}\). We present an experiment where a 1 mm quartz micropillar resonating at 3.6 MHz with an effective mass of 30 \(\mu\)g is cooled to 500 mK with a dilution refrigerator, and further optomechanically sideband-cooled to an effective temperature of 3 mK, corresponding to a mode thermal occupancy of 20 phonons. This nearly 1000-fold increase in the mass of an optomechanical system with respect to previous experiments near the quantum ground state opens new perspectives in the exploration of the quantum/classical border.