Active feedback cooling of a SiN membrane resonator by electrostatic actuation

TL;DR

This paper demonstrates active feedback cooling of a high-stress SiN membrane resonator using electrostatic actuation, reducing its effective temperature from room temperature to about 124mK, with potential for further improvements.

Contribution

It introduces a feedback cooling method for SiN membrane resonators exploiting trapped charges and dissipative feedback, achieving significant temperature reduction.

Findings

Achieved cooling of the membrane mode to 124mK

Implemented feedback using electrostatic actuation and trapped charges

Identified noise injection as a limiting factor for further cooling

Abstract

Feedback-based control techniques are useful tools in precision measurements as they allow to actively shape the mechanical response of high quality factor oscillators used in force detection measurements. In this paper we implement a feedback technique on a high-stress low-loss SiN membrane resonator, exploiting the charges trapped on the dielectric membrane. A properly delayed feedback force (dissipative feedback) enables the narrowing of the thermomechanical displacement variance in a similar manner to the cooling of the normal mechanical mode down to an effective temperature Te f f . In the experiment here reported we started from room temperature and gradually increasing the feedback gain we were able to cool down the first normal mode of the resonator to a minimum temperature of about 124mK. This limit is imposed by our experimental set-up and in particular by the the injection of the read-out noise into the feedback. We discuss the implementation details and possible improvements to the technique