Optomechanical coupling of a microwave cavity to a large mechanical resonator

Cavity optomechanics has developed to be a leading platform to study quantum properties of mechanical objects. One common objective is to cool a large mechanical resonator to its ground state and investigate quantum superpositions of these massive objects. Here, a 350 μm size high-stress Si₃N₄ membrane is capacitively coupled to a microwave cavity. At a temperature of 10 mK a Q factor of 10⁶ is obtained. Coupling between microwave photons and phonons in the mechanical resonator is obtained in fabricated devices. A process which can be influenced by the driving frequency. Besides this, noise reduction of 20 dBm over a bandwidth of 500 kHz is achieved by frequency locking the cavity with frequency modulation. Homodyne measurements are performed, a technique common in optical experiments. These steps will enable new optomechanical experiments, such as achieving mode swapping between the large membrane and a qubit, and to measure quantum fluctuations.