Equation Icon  2 S S − |S |2 = ℏ--[ψ †đ•Š [2r,0]ψ ⋅ Ī• †đ•Š [2r,0]Ī• − |ψ †đ•Š [2r,0]Ī• |2] x F xF 4 sqz sqz sqz ℏ2 ( 2) ℏ2 ( † † † 2) = --- |ψcĪ•s − ψsĪ•c| = --- ψ ψ ⋅ Ī• Ī• − |ψ Ī• | . (551 ) 4 4