Condensate wavefunction ($\psi (\mathbf{r})$)

A complex amplitude describing a coherent condensate in mean-field theory. In the convention $\int |\psi {|}^2{d}^{3}r=N$, its squared modulus is the condensate density. Dividing by $\sqrt{N}$ gives a normalized orbital; formulas for interaction strengths and nonlinear terms must use the same normalization convention.