Spin
Spin is the intrinsic angular momentum carried by elementary particles, atomic nuclei, and other quantum systems, independent of any motion through space. Unlike the spin of a classical top, it is quantized: measured along any axis, a particle's spin takes only discrete values set by its spin quantum number. The electron, proton, and neutron each have spin one-half.
Fermions and bosons
Spin divides all particles into two classes. Particles with half-integer spin, such as electrons, are fermions and obey the Pauli exclusion principle, which structures atoms and matter. Particles with integer spin, such as the photon, are bosons and can share a quantum state. Spin was inferred from the 1922 Stern-Gerlach experiment and proposed for the electron in 1925. Because a spin one-half system has exactly two basis states, it is a natural physical Qubit, and each of its states is labeled by a quantum number.
Sources
- The Nobel Prize in Physics 1943 (Otto Stern) (The Nobel Foundation, 1943)
- The Nobel Prize in Physics 1945 (Wolfgang Pauli) (The Nobel Foundation, 1945)
Cite this entry
"Spin." postquantum.wiki. Updated July 11, 2026. https://postquantum.wiki/spin@misc{pqwiki-spin,
title = {Spin},
howpublished = {\url{https://postquantum.wiki/spin}},
year = {2026},
note = {postquantum.wiki, updated 2026-07-11}
}