Soft-clamped silicon nitride string resonators at millikelvin temperatures

TL;DR

This paper demonstrates that soft-clamped silicon nitride string resonators can operate at millikelvin temperatures with extremely high quality factors, enabling highly sensitive force measurements and potential quantum applications.

Contribution

It shows that soft-clamped silicon nitride strings maintain high Q-factors at millikelvin temperatures, achieving over 10^9, and demonstrates their suitability for ultra-sensitive force sensing.

Findings

Q > 10^9 at 46 mK for silicon nitride strings

Force sensitivity of 9.6 zN/√Hz achieved

Thermal decoherence time of 0.38 s observed

Abstract

We demonstrate that soft-clamped silicon nitride strings with large aspect ratio can be operated at \si{\milli\kelvin} temperatures. The quality factors ($Q$) of two measured devices show consistent dependency on the cryostat temperature, with soft-clamped mechanical modes reaching $Q > 10^9$ at $46~\mathrm{mK}$. For low optical readout power, $Q$ is found to saturate, indicating good thermalization between the sample and the stage it is mounted on. Our best device exhibits a force sensitivity of $9.6~\mathrm{zN}/\sqrt{\mathrm{Hz}}$ and a thermal decoherence time of $0.38~\mathrm{s}$ which bode well for future applications such as nanomechanical force sensing and beyond.