Tunable coupling to a mechanical oscillator circuit using a coherent feedback network

TL;DR

This paper presents a cryogenic microwave feedback network with tunable coupling to a mechanical oscillator, enabling dynamic control of the system's decay rate and readout efficiency, advancing modular quantum device capabilities.

Contribution

It introduces a fully cryogenic, modular feedback network with a tunable controller that can rapidly switch between control and readout regimes, surpassing previous limitations.

Findings

Microwave decay rate modulated by a factor of 10

Tuning rate exceeds 10^4 times the mechanical response

System is simple to build and versatile for quantum applications

Abstract

We demonstrate a fully cryogenic microwave feedback network composed of modular superconducting devices connected by transmission lines and designed to control a mechanical oscillator coupled to one of the devices. The network features an electromechanical device and a 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, the tunable controller produces 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. The system is easy to build and suggests that some useful functions may arise most naturally at the network-level of modular, quantum electromagnetic devices.