Addition of quantum angular momenta
Independent commuting angular momenta combine as J=J₁+J₂.
Key knowledge
Independent commuting angular momenta combine as J=J₁+J₂. At fixed j₁,j₂, allowed total j runs in unit steps from |j₁−j₂| to j₁+j₂; coupled states expand in product states with Clebsch–Gordan coefficients that vanish unless m=m₁+m₂.
Values and equations
|j₁,j₂;j,m⟩=Σ_m₁,m₂ C_m₁,m₂^(j,m)|j₁,m₁⟩⊗|j₂,m₂⟩; Σ|C|²=1
- j₁,j₂,j,m₁,m₂,m
- Dimensionless angular-momentum labels
- C
- Dimensionless Clebsch–Gordan coefficient
- |…⟩
- Normalized coupled/product states
Conditions and scope
- Independent angular-momentum representations; component cross-commutators vanish.
- Coefficient signs depend on a phase convention; squared coefficients give product-basis probabilities.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Quantum Mechanics (2016): Clebsch–Gordon coefficients: Equations 6.22–6.28: change of basis, projection rule, triangle range and normalization.
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Entry details
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