Cryogenic measurements of millimeter-wave optomechanical circuits

In the current paradigm of quantum cavity optomechanics, the relatively weak parametric coupling between an electromagnetic cavity and a mechanical resonator is mediated by an external pump. While this strong cavity drive acts to enhance the optomechanical interaction, it obscures its intrinsic nonlinearity, restricting these systems to bilinear operations on Gaussian states. By increasing this coupling so that it dominates the decoherence rates of the system, one could instead use the fundamental optomechanical nonlinearity to prepare the mechanical resonator into complex, non-Gaussian states. This has potential applications in quantum metrology, information, and tests of quantum mechanics itself. Here I will present our efforts towards reaching this regime using superconducting millimeter-wave optomechanical circuits. Based on previous microwave vacuum gap capacitor designs, these devices are optimized to enhance not only their optomechanical coupling, but also their intrinsic mechanical quality factors. I will present measurements of these millimeter-wave devices at dilution refrigerator temperatures using a waveguide-coupled cryogenic amplifier.  These novel measurements of millimeter-wave optomechanical cavities demonstrate the first steps towards the ultimate goal of performing quantum-coherent control of mechanical motion at the single-photon level.