The spin of the photon is defined as the coefficient of ℏ ℏ in the spin angular momentum calculation. A photon has spin 1 if it is in the | R ⟩ ⟩ state and −1 if it is in the | L ⟩ ⟩ state. The spin operator is defined as the outer product S ^ ^ = d e f | R ⟩ ⟩ ⟨ ⟨ R | − − | L ⟩ ⟩ ⟨ ⟨ L | = ( 0 − − i i 0 ) .