报告人简介：

　　Klaus von Klitzing教授，德国物理学家，1943年生。他在1980年研究二维电子气在强磁场中的输运性质时发现了量子霍尔效应，并因此获得1985年诺贝尔物理学奖。国际计量标准化组织在1990年决定使用量子霍尔电阻作为电阻的国际标准，并用他的名字命名（克里青常数）。这一发现的重要性还在于量子霍尔电阻的精确性与普适性引发了规范不变性、几何相位和拓扑不变量等重要理论概念在许多体系中的应用，相关研究对近年来拓扑绝缘体和拓扑半金属等新物态的发现起到了促进作用。von Klitzing教授在1972年获得德国乌兹堡大学博士学位，1980-1985年任慕尼黑工大教授，从1985年起一直在位于斯图加特的马普固态研究所担任研究主任，主要从事低维电子体系方面的研究。

　　Abstract:

　　The International System of Units (SI units) forms the basis for all measurements. With the Meter Convention in 1875 a worldwide system of units was introduced with prototypes for the meter and kilogram kept at the Bureau International des Poids et Mesures in Sevres. Even today the kilogram prototype is by definition the unit of mass whereas the unit of length has been replaced in 1983 by a fixed value for the velocity of light (in combination with the well-known time unit from atomic clocks).

　　Long-term comparisons of the kilogram prototype with other mass standards indicate, that the prototype is not stable with time so that the General Conference on Weights and Measures at his last meeting in November 2014 published a resolution with the recommendation to define the SI units  in terms of invariants of nature; the new definitions will be based on fixed numerical values of the Planck constant (h), the elementary charge (e), the Boltzmann constant (k), and the Avogadro constant (NA), respectively. A prerequisite for such a change is the precise experimental realization of practical standards on the basis of natural constants.

　　The quantized Hall resistance (Nobel Prize 1985) plays a crucial role for the implementation of a new SI system since this quantum resistance can be used not only for high precision realizations of electrical standards but also for a new realization of a kilogram by comparing electrical and mechanical forces with the Watt balance.

　　The talk summarizes the application of the quantum Hall effect in metrology with the focus on the replacement of the kilogram by a fixed value for the Planck constant.