Division of Physical Chemistry, Chemical Center, P.O. Box 124, University of Lund, SE 22100 Lund, Sweden.
Phys Chem Chem Phys. 2012 Feb 7;14(5):1677-84. doi: 10.1039/c2cp22173j. Epub 2011 Dec 21.
The classical Stern-Gerlach experiment is analyzed with an emphasis on the spin dynamics. The central question asked is whether there occurs a relaxation of the spin angular momentum during the time the particle passes through the Stern-Gerlach magnet. We examine in particular the transverse relaxation, involving angular momentum exchange between the spin of the particles and the spins of the magnet. A method is presented describing relaxation effects at an individual particle level. This leads to a stochastic equation of motion for the spins. This is coupled to a classical equation of motion for the particle translation. The experimental situation is then modeled through simulations of individual trajectories using two sets of parameter choices and three different sets of initial conditions. The two main conclusions are: (A) if the coupling between the magnet and the spin is solely described by the Zeeman interaction with the average magnetic field the simulations show a clear disagreement with the experimental observation of Stern and Gerlach. (B) If one, on the other hand, also allows for a T(2) relaxation time shorter than the passage time one can obtain a practically quantitative agreement with the experimental observations. These conclusions are at variance with the standard textbook explanation of the Stern-Gerlach experiment.
经典的斯特恩-格拉赫实验分析强调了自旋动力学。所提出的核心问题是，在粒子穿过斯特恩-格拉赫磁体的过程中，自旋角动量是否会发生弛豫。我们特别研究了涉及粒子自旋和磁体自旋之间角动量交换的横向弛豫。本文提出了一种描述单个粒子水平上弛豫效应的方法。这导致了自旋的随机运动方程。该方程与粒子平移的经典运动方程耦合。然后通过使用两组参数选择和三组不同的初始条件对单个轨迹进行模拟来模拟实验情况。两个主要结论是：(A)如果仅通过与平均磁场的塞曼相互作用来描述磁体和自旋之间的耦合，那么模拟结果与斯特恩和格拉赫的实验观察结果存在明显分歧。(B)另一方面，如果还允许弛豫时间 T(2)短于通过时间，则可以与实验观察结果获得几乎定量的一致。这些结论与斯特恩-格拉赫实验的标准教科书解释不一致。
