核绝热去磁制冷

Refrigeration by adiabatic nuclear demagnetization

温度是最基本的物理量之一,在科学研究中,将研究对象放置在低温环境中是一个非常常见的方法。更低的温度有助于发现低能量尺度的量子多体系统的新演生现象,也有助于在更低的热噪声下实现更高的实验分辨率。低温实验工作者有两个基本任务,一个是在低温环境下发现新的物理,另一个是提供低温环境和创造新的低温环境。在液氦或者干式制冷提供前级预冷环境的基础上,核绝热去磁等制冷原理被提出和使用。低温设备的无液氦消耗化,是与氦液化和稀释制冷同等重要的低温制冷突破。氦于1908年被液化,20世纪60年代中国有能力液化氦;同个时期,稀释制冷机被发明,中国近期正在发展稀释制冷技术。文章讨论了核绝热去磁制冷的基本原理,回顾了干式核绝热去磁技术的出现背景,并介绍了这种设备的一次搭建尝试。这次在中国的尝试,成功地实现了世界最低温度的无液氦消耗制冷机。

Temperature is one of the most fundamental physical quantities,and low temperature environments serve as a typical approach for frontier scientific explorations.Lower temperature environments help to discover novel phenomena in low-energy scale quantum manybody systems,and to achieve higher experimental resolutions at lower thermal noise levels.There are two basic missions for low temperature experimentalists:discovering new physics at low temperatures,and maintaining low temperature environments or creating better ones.Precooling by liquid helium or cryogen-free methods,refrigeration principles such as adiabatic nuclear demagnetization have been proposed and verified.The process of cryogen-free,is as important as the liquefaction of helium and the dilution refrigeration for low temperature refrigeration.In 1908,helium was first liquefied while China was able to achieve stable~4 K environments in the 1960s.During that time,dilution refrigerators were invented elsewhere.China is investing on how to build them nowadays.This article covers the principles of adiabatic nuclear demagnetization and introduces what has led to the cryogen-free adiabatic nuclear demagnetization technique.Additionally,it describes a successful attempt to build such a refrigerator in China,which is the lowest temperature cryogen-free refrigerator in the world.