Magnetic cooling and vibration isolation of a sub-kHz mechanical resonator

TL;DR

This paper demonstrates advanced cooling and vibration isolation of a sub-kHz mechanical resonator to near 1 millikelvin, enabling quantum mechanical tests with high quality factors and minimal vibrations.

Contribution

It presents a novel combination of magnetic cooling and vibration isolation techniques to achieve ultra-low temperatures and low-vibration environments for mechanical quantum tests.

Findings

Silicon cantilever cooled to approximately 1 mK.

Quality factor of cantilever reaches 4×10^4 at 2 mK.

Thermal motion detected down to 20 mK, limited by readout coupling.

Abstract

We report recent progress towards the realization of a sub-mK, low-vibration environment at the bottom stage of a dry dilution refrigerator for use in mechanical tests of quantum mechanics. Using adiabatic nuclear demagnetization, we have cooled a silicon cantilever force sensor to $T\approx 1$ mK. The temperature of the tip-holder of the cantilever chip was determined via a primary magnetic flux noise thermometer. The quality factor of the cantilever continues to increase with decreasing temperature, reaching $Q\approx 4\cdot 10^4$ at $2$ mK. To demonstrate that the vibration isolation is not compromised, we report the detection of the thermal motion of the cantilever down to $T \approx 20$ mK, only limited by the coupling to the SQUID readout circuit. We discuss feasible improvements that will allow us to probe unexplored regions of the parameter space of continuous spontaneous localization models.