A Sub-kHz Mechanical Resonator Passively Cooled to 6 mK

TL;DR

This paper demonstrates passive cooling of a low-frequency mechanical resonator to 6.1 mK using nuclear demagnetization, enabling studies of quantum mechanics and force detection at ultra-low temperatures.

Contribution

First to passively cool a low-frequency mechanical resonator to sub-millikelvin temperatures using nuclear demagnetization.

Findings

Resonator cooled to 6.1 mK confirmed by thermal motion detection.

Thermal motion remains distinguishable from background noise at lowest temperatures.

Motion is thermally distributed at these ultra-low temperatures.

Abstract

Highly coherent mechanical resonators are invaluable to ultrasensitive detection techniques by enabling detection of small forces. Studying mechanical resonators in a thermal equilibrium state at millikelvin temperatures provides a promising path to increase their coherence time. Here, we passively cool a 700 Hz massive (1.5 ng) mechanical cantilever down to 6.1(4) mK by means of nuclear demagnetization, as confirmed by detecting its thermal motion via a lock-in based detection scheme. At the lowest temperatures the thermal motion of the resonator is still clearly distinguishable from the background noise. Our data analysis confirms that at these temperatures the motion is still thermally distributed. These results pave the way for passive cooling low-frequency resonators to the sub-millikelvin regime, which would enable new tests of quantum mechanics and advances in ultrasensitive force detection.