Which atomic experiment measured the quantized deflection of silver atoms in a magnetic field?

The Stern–Gerlach experiment measured the quantized deflection of silver atoms in a magnetic field.

Otto Stern and Walther Gerlach performed the experiment in 1922. A beam of silver atoms passed through a nonuniform magnetic field and split into two distinct parts on a detector. Classical models had suggested a continuous spread of orientations, whereas the separated traces indicated quantized angular-momentum components.

The result is now understood through electron spin. Silver atoms have one unpaired outer electron, so the beam’s magnetic behavior is dominated by that electron’s spin. The original experiment preceded the modern terminology of spin, but it became a foundational demonstration of space quantization and measurement in quantum mechanics.