Efficient microwave measurement of superconducting optomechanical circuits

Optomechanical interactions between electromagnetic modes and mechanical resonators have proven to be a valuable testbed for measurement and control of linear quantum systems. In this context, the light is considered as a meter that probes and influences the quantum state of the mechanical object. Reaching quantum limits of measurement and control therefore requires both that the optomechanical coupling overwhelms any decoherence and that the light is measured with sufficiently high efficiency. In microwave optomechanical systems, the first requirement has been demonstrated, but the second remains an experimental challenge, with state-of-art continuous linear measurements of microwave fields struggling to exceed 50% efficiency. Here I report recent progress to increase microwave measurement efficiencies to enable new regimes of ponderomotive squeezing and displacement sensing beyond the standard quantum limit.