Vibration isolation with high thermal conductance for a cryogen-free dilution refrigerator

TL;DR

This paper introduces a vibration isolation system for cryogen-free dilution refrigerators that achieves low vibrational noise and high thermal conductance, enabling ultra-sensitive measurements at millikelvin temperatures.

Contribution

The authors present a novel mechanical low-pass filter design that reduces vibrations while maintaining high thermal conductance in cryogen-free dilution refrigerators.

Findings

Vibration noise levels are significantly reduced near the resonator.

The system maintains a base temperature of 8 mK, cooling to 10.5 mK.

Force sensitivity below 500 zN/√Hz achieved.

Abstract

We present the design and implementation of a mechanical low-pass filter vibration isolation used to reduce the vibrational noise in a cryogen-free dilution refrigerator operated at 10 mK, intended for scanning probe techniques. We discuss the design guidelines necessary to meet the competing requirements of having a low mechanical stiffness in combination with a high thermal conductance. We demonstrate the effectiveness of our approach by measuring the vibrational noise levels of an ultrasoft mechanical resonator positioned above a SQUID. Starting from a cryostat base temperature of 8 mK, the vibration isolation can be cooled to 10.5 mK, with a cooling power of 113 $\mu$W at 100 mK. We use the low vibrations and low temperature to demonstrate an effective cantilever temperature of less than 20 mK. This results in a force sensitivity of less than 500 zN/$\sqrt{\mathrm{Hz}}$, and an integrated frequency noise as low as 0.4 mHz in a 1 Hz measurement bandwidth.