Optomechanical measurement of a millimeter-sized mechanical oscillator near the quantum limit

Cavity optomechanics is a tool to study the interaction between light and micromechanical motion. Here we observe near-quantum limited optomechanical physics in a truly macroscopic oscillator. As the mechanical system, we use a mm-sized piezoelectric quartz disk oscillator. Its motion is coupled to a charge qubit which translates the piezo-induced charge into an effective radiation-pressure interaction between the disk and a microwave cavity. We measure the thermal motion of the lowest mechanical shear mode at 7MHz down to 35 mK, corresponding to roughly 100 quanta in a 20mg oscillator. The work opens up opportunities for macroscopic quantum experiments.