That the wave function is separable means that ψ ψ factorizes in the form ψ ψ ( r 1 , r 2 , t ) = ψ ψ A ( r 1 , t ) ψ ψ B ( r 2 , t ) . Then it follows that also R factorizes, and the system's total quantum potential becomes the sum of the quantum potentials of the two particles.