In quantum physics, what experiment split silver atoms into separate beams according to spin?

In quantum physics, the Stern–Gerlach experiment split silver atoms into separate beams according to spin.

Otto Stern and Walther Gerlach carried out the experiment in Frankfurt in 1922. They sent a beam of silver atoms through a nonuniform magnetic field and detected the atoms on a screen. Instead of forming a continuous smear, the beam separated into two distinct parts.

The result showed that the component of angular momentum along the chosen measurement direction is quantized. For silver atoms in the experiment, the relevant unpaired electron gives two possible outcomes associated with spin-½. The apparatus therefore became a landmark demonstration of space quantization and quantum measurement.

The experiment is often described as directly photographing an electron’s spin, but that is imprecise. It measured the deflection of whole silver atoms, whose magnetic moments were linked to their electrons. It also differs from the double-slit experiment, which demonstrates interference rather than spin-dependent beam splitting.