§ Einstein-de Haas effect
I learnt of this from hacker news. This is some crazy experiment that shows
that the 'quantum angular momentum' (spin) and the 'classical angular momentum'
need to be conserved together for physics to work out:
There's an experiment that transfers that angular momentum all the way up to
macroscopic levels. By magnetizing a cylinder of iron, all the spins start
pointing in the same direction. By conservation of angular momentum, the
cylinder itself has to start spinning in the opposite direction. I'm very
fond of this experiment, because it magnifies a strange quantum phenomenon to
the classical level.
So, my understanding of the experiment is:
- classical angular momentum and quantum angular momentum are related.
- quantum angular momentum is decomposed into spin and orbital angular momentum.
- for something like iron, spin is 96% of magnetization
- angular momentum is proportional to magnetization
- So, the experiment measures the spin (mostly) in terms of the classical spinning of the cylinder.
§ References