The Stern-Gerlach-Experiment (SGE) performed in 1922 is a seminal benchmark experiment of quantum physics providing evidence for several fundamental properties of quantum systems. Based on the knowledge of today we illustrate the different benchmark results of the SGE for the development of modern quantum physics and chemistry. The SGE provided the first direct experimental evidence for angular momentum quantization in the quantum world and therefore also for the existence of directional quantization of all angular momenta in the process of measurement. Furthermore, it measured for the first time a ground state property of an atom, it produced for the first time a fully “spin-polarized” atomic beam, and it also revealed the electron spin, even though this was not realized at the time. The SGE was the first fully successful molecular beam experiment where the kinematics of particles can be determined with high momentum-resolution by beam measurements in vacuum. This technique provided a kind of new kinematic microscope with which inner atomic or nuclear properties could be investigated. Historical facts of the original SGE are described together with early attempts by Einstein, Ehrenfest, Heisenberg, and others to reveal the physical processes creating directional quantization in the SGE. Heisenberg’s and Einstein’s proposals of an improved multi-stage SGE are presented. The first realization of these proposed experiments by Stern, Phipps, Frisch and Segrè is described. The experimental set-up suggested by Einstein can be considered as an anticipation of a Rabi-apparatus with varying fields. Recent theoretical work by Wennerström and Westlund, by Devereux and others, is mentioned in which the directional quantization process and possible interference effects of the two different spin states are investigated. In full agreement with the results of the new quantum theory directional quantization appears as a general and universal feature of quantum measurements. One experimental example for such directional quantization in scattering processes is shown. Last not least, the early history of the “almost” discovery of the electron spin in the SGE is revisited.

中文翻译：

---

重新研究了斯特恩·盖拉赫（Stern-Gerlach）实验

1922年进行的斯特恩·格拉赫拉赫实验（SGE）是量子物理学的开创性基准实验，为量子系统的几个基本特性提供了证据。根据今天的知识，我们为现代量子物理学和化学的发展说明了SGE的不同基准结果。SGE为量子世界中的角动量量化提供了第一个直接的实验证据，因此也为测量过程中所有角动量的定向量化提供了依据。此外，它首次测量了原子的基态特性，并首次产生了完全“自旋极化”的原子束，并且还揭示了电子自旋，即使当时还没有实现。SGE是第一个完全成功的分子束实验，其中可以通过在真空中进行束测量以高动量分辨率确定颗粒的运动学。该技术提供了一种新型的运动显微镜，可以用来研究内部原子或核特性。描述了原始SGE的历史事实以及Einstein，Ehrenfest，Heisenberg等人的早期尝试，以揭示在SGE中产生定向量化的物理过程。提出了海森堡和爱因斯坦提出的改进多级SGE的建议。Stern，Phipps，Frisch和Segrè描述了这些拟议实验的第一个实现。爱因斯坦建议的实验设置可以被认为是对具有不同场强的拉比仪器的期待。提到了Wennerström和Westlund以及Devereux等人的最新理论工作，其中研究了两种不同自旋态的方向量化过程和可能的干扰效应。与新的量子理论的结果完全一致，定向量化似乎是量子测量的通用特征。显示了在散射过程中进行这种定向量化的一个实验示例。最后，SGE中“几乎”发现了电子自旋的早期历史也被重新审视。与新的量子理论的结果完全一致，定向量化似乎是量子测量的通用特征。显示了在散射过程中进行这种定向量化的一个实验示例。最后，SGE中“几乎”发现了电子自旋的早期历史也被重新审视。与新的量子理论的结果完全一致，定向量化似乎是量子测量的通用特征。显示了在散射过程中进行这种定向量化的一个实验示例。最后，SGE中“几乎”发现了电子自旋的早期历史也被重新审视。