Quantized circulation
= Quantized circulation
{title2=$\oint\mathbf u\cdot d\mathbf l=2\pi\hbar q/m$}
Single-valuedness of the condensate field gives total <complex argument> change $2\pi q$ on a closed loop avoiding zeros, where $q$ is an integer <winding number>. Integrating the <superfluid velocity> around that loop gives the displayed <circulation>. It is unchanged by smooth deformations of the loop that do not cross a <quantum vortex>.