Refrigerator cools to 50 microkelvin

A double‐stage nuclear demagnetization refrigerator promises to allow experiments at temperatures an order of magnitude lower than previously available. The new cooling device can not only reach record low electronic temperatures of 50 microkelvins but can maintain these temperatures long enough in an apparatus large enough to cool samples within it. The apparatus was developed at the Kernforschungsanlage Jülich in West Germany. Experimenters there have cooled about 2 kg of copper to an electronic temperature of 48 microkelvins and kept it below 60 microkelvins for more than two days. At the same time, in Japan, a group from the Institute for Solid State Physics at the University of Tokyo has reported equally low temperatures with a similar method but in a much smaller device.