Figure 1. Microwave optomechanics with a 3D superconducting cavity and a millimetre-sized membrane.

(a) Electron microscope image of a 50-nm-thick SiN_x membrane. (b) One half of the Al cavity with an SMA connector for reflection measurements. The dimensions of the cavity are 28 × 28 × 8 mm. (c) Schematic showing the placement of the membrane over the antenna pads. The Al coating of the membrane forms a capacitor with the antennas below. (d) A complete assembly. The membrane is positioned in the centre of the cavity, supported by a sapphire substrate patterned with the Al antenna. (e) An optical microscope image looking from the top showing the Al-coated membrane and the underlying antenna pads. (f) Effective lumped-element model of the cavity and membrane. By changing the effective shunt capacitance, the frequency of the 3D cavity is modulated by the mechanical motion of the membrane.