Aluminum nuclear demagnetization refrigerator for powerful continuous cooling

TL;DR

This paper introduces a novel aluminum nuclear demagnetization refrigerator designed for continuous, powerful cooling below 1 mK, enabling more accessible microkelvin range experiments in quantum science.

Contribution

It presents a dual-stage continuous NDR with minimized thermal resistance and eddy current heating susceptibility, achieving high cooling power and rapid cycling.

Findings

Cooling power of approximately 40 nW at 560 μK

Achieves continuous cooling with minimal electronic temperature offset

Reaches microkelvin temperatures within six days from room temperature

Abstract

Many laboratories routinely cool samples to 10 mK, but relatively few can cool condensed matter below 1 mK. Easy access to the microkelvin range would propel fields such as quantum sensors and quantum materials. Such temperatures are achieved with adiabatic nuclear demagnetization. Existing nuclear demagnetization refrigerators (NDR) are ``single-shot'', and the recycling time is incompatible with some sub-mK experiments. Furthermore, a high cooling power is required to overcome the excess heat load of order nW on NDR pre-cooled by cryogen-free dilution refrigerators. We report the performance of an aluminum NDR designed for powerful cooling when part of a dual stage continuous NDR (CNDR). Its thermal resistance is minimized to maximize the cycling rate of the CNDR and consequently its cooling power. At the same time, its susceptibility to eddy current heating is minimized. A CNDR based on two of the aluminum NDR presented here would achieve a cooling power of approximately 40 nW at 560 $\mu$K less than six days after cooling from room temperature, with a small offset in electronic temperature that decreases as the time-dependent heat load decays.