Spin and the Stern–Gerlach Experiment
In 1922 Otto Stern and Walther Gerlach sent silver atoms through an uneven magnet and saw them split into exactly two spots, not a smear. The cause is spin, a built-in magnetism of the electron that always measures as one of two values along any axis you pick. Magnets in a row show that a new question erases the answer to an old one, just like a qubit.
Why is spin the most natural qubit in nature?
A qubit needs exactly two outcomes. Nature hands us one ready-made. It is called spin. Measure an electron's spin along any direction and you always get one of just two answers, called "up" and "down."
Spin is used in real quantum hardware. Some qubits are single electron spins held in silicon. MRI scanners in hospitals read the spins of atoms in your body. And the experiment that first showed this two-answer rule is one of the cleanest in all of physics.
- What would a spinning top do in a magnet?
- What did Stern and Gerlach actually see?
- What happens when you line up magnets in a row?
- Worked example: count the atoms through three magnets
- Run it: Z magnet, then Z againINTERACTIVE
- Try this: up atoms, then X, then ZINTERACTIVE
- Try this: flip a spin with a magnetic fieldINTERACTIVE
- How do magnet angles match qubit turns?
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