Experiments with Spin Half Particles The Stern-Gerlach Experiment, Larmor Precession and Magnetic Resonance

Abstract

The analysis of the spin half problem is of great significance because it is not only of tremendous practical importance but it also allows us to understand some of the fundamental postulates of quantum mechanics.

A replica of the postcard sent by Walther Gerlach to Niels Bohr on February 8, 1922. The left-hand image of the beam profile without the magnetic field shows the effect of the finite width of the collimating slit. The right-hand image shows the beam profile with the magnetic field. Only in the centre of the apparatus is the magnitude of the magnetic field gradient sufficiently strong to cause splitting. The pattern is smeared because of the range of speeds of the atoms coming from the oven. Translation of the message: “My esteemed Herr Bohr, attached is the continuation of our work [vide Zeitschr. f. Phys. 8, 110 (1921)]: the experimental proof of directional quantization. We congratulate you on the confirmation of your theory! With respectful greetings. Your most humble Walther Gerlach.”

Adapted from J.S. Townsend, A Modern Approach to Quantum Mechanics, McGraw-Hill, New York (1992). The photograph was kindly provided by the Niels Bohr Archives in Copenhagen.