Condensate depletion ($n-n_0$)

Occupation outside the macroscopically occupied condensate mode, caused by interactions or thermal excitations. A weak homogeneous three-dimensional Bose gas has zero-temperature depletion fraction $8\sqrt{n{a}_s^3}/(3\sqrt{\pi })$ in the leading dilute-gas approximation. Depletion measures single-particle mode occupation, not directly the superfluid fraction.