Spin one-half and Pauli operators
A spin one-half state has two outcomes along a chosen axis.
Key knowledge
In the S_z eigenbasis, a spin one-half angular momentum is represented by S_i = (ħ/2)σ_i. The Pauli matrices have eigenvalues ±1, so an axis measurement gives ±ħ/2.
Values and equations
S_i = (ħ/2)σ_i; σ_x = [[0,1],[1,0]]; σ_y = [[0,−i],[i,0]]; σ_z = [[1,0],[0,−1]]
- S_i
- Spin angular-momentum operator J s
- ħ
- Reduced Planck constant J s
- σ_i
- Dimensionless Pauli matrix
- i
- Imaginary unit in matrix entries; axis index in S_i/σ_i
Conditions and scope
- Use the displayed ordered S_z basis and ordinary spin one-half Hilbert space.
- Intrinsic spin is quantum angular momentum; no literal rotating-sphere model is asserted.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Feynman 11–1 and Table 11–1: matrices and ±ħ/2 basis; OpenStax equation 8.27 and s = 1/2.
2026-10-10 · Two-dimensional spin representation only; magnetic moments, g-factors and higher spins excluded.
Entry details
Permanent link to this entry ↗- Record identity
- physics-spin-half
- Revision
- university-reference.1
- Structured reference record
- University reference · University core expansion