PTB News 2/2005 (107 kB) PTB News 2/2005, English edition, Issue August 2005The PTB microkelvin facility in Berlin has been set up and successfully tested. It is now possible to maintain temperatures of only a few millionths of a degree above absolute zero. In addition, the behaviour of condensed matter in strong magnetic fields can be investigated in this temperature range.
The novel threefold nuclear stage, developed in cooperation with Max-Planck-Institute for Physics of Complex Systems in Dresden, consists of concentrically arranged cylinders of high-purity copper and aluminium. The stage can cool a “payload” down to temperatures in the lower microkelvin range by means of adiabatic demagnetization of the nuclear moments from 8.5 Tesla down to a few millitesla.
Already in first tests using a thermodynamically optimized demagnetization function lattice temperatures below 25 mK were achieved and maintained for several hours. Expensive measures were taken for HF screening, to attenuate mechanical vibrations and to minimize an internal heat leak by the appropriate selection of materials. The measures have reduced the heat leak to below 1.5 nW.
Thanks to the more effective exploitation of the field of the first magnet the concentric set-up of the threefold cooling nuclear stage allows the application of a second large magnet below the cooling stage. With this magnet, which has a very high field homogeneity, the magnetic behaviour of ultra-cold matter can be investigated in magnetic fields up to 9 Tesla – in this form currently a unique experimentation environment.
In the focal point of the investigations with the cooperation partners from Dresden, Heidelberg, and Berlin are magnetic field induced macroscopic quantum effects and basic metrological questions concerning definition and measurement of the base unit temperature as well as their quantum mechanical limitations.