Controlling a mechanical oscillator with a tunable coherent feedback network

We demonstrate a fully cryogenic microwave feedback network composed of modular superconducting devices interconnected by transmission lines and designed to control a mechanical oscillator coupled to one of the devices. The network is partitioned into an electromechanical device and a dynamically tunable controller that coherently receives, processes and feeds back continuous microwave signals that modify the dynamics and readout of the mechanical state. While previous electromechanical systems represent some compromise between efficient control and efficient readout of the mechanical state, as set by the electromagnetic decay rate, this flexible controller yields a closed-loop network that can be dynamically and continuously tuned between both extremes much faster than the mechanical response time. We demonstrate that the microwave decay rate may be modulated by at least a factor of 10 at a rate greater than $10^4$ times the mechanical response rate.