Written this way, the probability density is ρ ρ = Ψ Ψ ∗ ∗ Ψ Ψ = R 2 and the probability current is: j = ℏ ℏ 2 m i ( Ψ Ψ ∗ ∗ ∇ ∇ Ψ Ψ − − Ψ Ψ ∇ ∇ Ψ Ψ ∗ ∗ ) = ℏ ℏ 2 m i ( R e − − i S / ℏ ℏ ∇ ∇ R e i S / ℏ ℏ − − R e i S / ℏ ℏ ∇ ∇ R e − − i S / ℏ ℏ ) = ℏ ℏ 2 m i [ R e − − i S / ℏ ℏ ( e i S / ℏ ℏ ∇ ∇ R + i ℏ ℏ R e i S / ℏ ℏ ∇ ∇ S ) − − R e i S / ℏ ℏ ( e − − i S / ℏ ℏ ∇ ∇ R − − i ℏ ℏ R e − − i S / ℏ ℏ ∇ ∇ S ) ] .