Optomechanics with massive resonators

The interface between quantum mechanics and gravity remains an open question. Indirect measurements studying gravity originating from source masses in quantum states could probe this interface, however, are challenging as quantum coherence is quickly lost for large systems ensuring small masses must be utilized, and detecting a gravity signature from a such small objects is hard. Micromechanical oscillators, already demonstrated as sensors with high force sensitivity and able to be prepared in a ground state, are ideally suited to realizing these experiments. Here we detail an optomechanical setup with gold spheres weighing a few mg on silicon nitride membranes coupled to three-dimensional microwave cavities. These mass loaded membranes vibrate at 2 kHz in the drum mode. We show thermalization of these massive oscillators to mK temperatures, and optomechanical side-band cooling with the goal to prepare the oscillators in their ground state. Two such oscillators in close proximity pave the way for measurements of classical gravity between milligram masses in quantum states.