In a homogeneous superfluid, a phase twist with amplitude results in a constant gradient of the phase, that is, a constant velocity, whereas in a supersolid (b, c), the kinetic energy can be minimized by accumulating most of the phase variation in the low-density regions. The grey and green areas represent the number density and the kinetic energy density, respectively, whereas the phase profile is plotted in red. The superfluid fraction is the ratio of the area under the green curve to that of the homogeneous case.
